Three-Dimensionally Printed Catalytic Structures

Abstract

Three-dimensionally (3D)-printed catalytic structures are revolutionizing catalysis and chemical engineering. Unlike traditional supports, modern triply periodic minimal surfaces (TPMS), lattices, and fractals actively influence mass and heat transfer and flow distribution. This review summarizes advancements in the classification, design, fabrication, and application of 3D-printed catalysts over the past decade. The article covers various constructive types (supports, integrated phases, multifunctional reactors) and materials (polymers, ceramics, metals, hybrids), along with fabrication techniques compliant with ISO/ASTM standards (FDM, SLA, DIW, SLM, EBM). It emphasizes post-processing and functionalization strategies (impregnation, calcination, sulfonation) and characterization tools (SAXS, CT, synchrotron-based techniques). A critical comparison highlights advantages, including tunable geometry, improved hydrodynamics, lower pressure drop, enhanced durability, and reproducibility. Three-dimensionally printed catalysts are an interdisciplinary platform combining materials science, chemical engineering, and digital manufacturing. They hold promise for sustainable chemistry, modular production, CO₂ utilization, photocatalysis, and biocatalysis, making them a key innovation for future catalytic reactors.

1. Introduction

The catalytic industry is undergoing transformation driven by advances in three-dimensional (3D) printing, i.e., additive manufacturing (AM). Traditionally, industrial heterogeneous catalysts are shaped as pellets, extrudates, monolithic blocks, or foams, with limited control over the geometry of pores and channels. The catalyst’s shape and internal architecture critically affect process efficiency: they determine the accessibility of active sites, the contact area with the reactants, flow hydrodynamics, mass and heat transfer, and the pressure drop (ΔP) in the reactor [1]. Three-dimensional printing (additive manufacturing) opens fundamentally new pathways to optimize these parameters. The layer-wise fabrication paradigm affords unprecedented design freedom for catalytic structures, enabling forms of virtually any complexity with prescribed internal channel and pore architectures [2,3]. In printed architectures, one can deliberately increase surface area and porosity, spatially distribute active components, and even implement through thickness gradients of properties. As a result, catalytic activity and selectivity can be enhanced, heat and mass transfer can be improved, and the energy required to pump reactants can be reduced due to lower hydraulic resistance of the catalytic bed [4]. According to Shell, AM can accelerate the development of new catalysts and provide breakthrough solutions for otherwise-hard-to-implement reactions by offering macro- and microstructures that are not attainable using conventional forming routes [3].

Over the past decade (2015–2025), catalyst 3D printing has progressed from concept to active research and early industrial adoption. New material formulations and printing methods have been developed to fabricate catalytically active elements or supports that are subsequently functionalized with active phases. Laboratory studies have compared 3D-printed structures with classical granular and monolithic catalysts [1]. In a number of cases, pronounced advantages have been demonstrated: for example, printed lattice supports can deliver comparable conversion at a substantially lower pressure drop together with a more uniform temperature field compared to packed beds of particles [5,6]. By 2019–2023, the first pilot-to-industrial implementations appeared: BASF introduced a 3D-printed catalyst for SO₂ oxidation in a commercial process, achieving savings in energy and resources [4]. In parallel, major oil and gas companies (e.g., Rosneft) have been patenting 3D-printing approaches for complex catalyst geometries designed using computational fluid dynamics (CFD) [2]. These developments signal the onset of a new stage in catalytic research in which the catalyst’s geometry and structural characteristics become full-fledged design variables for process optimization. They also have the potential to further deepen understanding of underlying reaction mechanisms, as has occurred previously (Figure 1).

Figure 1. Relationship between practical catalysis knowledge and theoretical understanding [7].

This review provides a comprehensive analysis of 3D-printed catalytic structures. We summarize their classification and types, the AM methods employed, materials and required post-processing, approaches to functionalizing printed preforms, and methods for structural and compositional characterization. Dedicated sections address principles of geometrical design of catalytic structures, advantages of AM relative to traditional approaches, and current industrial applications, company case studies, patent solutions, and promising development directions. The discussion is illustrated using publications primarily from 2015–2025, including laboratory results, pilot-scale trials, and techno-economic assessments. Accordingly, the review targets specialists in catalysis, chemical engineering, materials science, and biotechnology who are interested in leveraging additive manufacturing to create next-generation, high-performance catalytic systems.

2. Classification of 3D-Printed Catalytic Structures

Three-dimensionally printed catalytic structures can be classified along several axes: by their role in the process (support versus directly via the active catalytic element), by shape/geometry, and by manufacturing route. The principal types realized via 3D printing in catalytic applications are summarized below:

Three-dimensionally printed granules and pellets with complex shape. These are individual catalytic bodies (from a few millimeters up to centimeters) with optimized morphology, for example, spheres with internal channels, star-shaped or lattice pellets, and related forms. Such bodies are intended for packed-bed reactors in place of conventional cylindrical extrudates or tablets (Figure 2a) [2,8]. Three-dimensional printing enables pellet designs with increased surface area and engineered internal voids, promoting faster diffusion of reactants into the particle while simultaneously lowering interparticle flow resistance. An illustrative case is the patented “granules” from PJSC Rosneft, designed using CFD: the optimized pellet comprises a branched network of channel like pores that affords a high surface-to-volume ratio and, consequently, increased activity [2]. Printed pellets may be fabricated from a support material (e.g., alumina) subsequently impregnated with active components or directly from a catalytic composition.

Figure 2. Examples of catalyst structures: (a) Example of a complex-shaped pellet [8]; (b) example of spiral catalytic static mixers [9]; (c) example of the internal structure of an enzymatic reactor [10].

Monolithic blocks with regular lattice architecture. These relatively large components (up to tens of centimeters)—analogues of ceramic honeycombs or foams for flow reactors—exhibit a periodic open cellular structure (POCS). In contrast to conventional stochastic foams, 3D-printed lattices feature narrowly distributed cell sizes and shapes, enabling optimization of the tradeoff between surface area and hydraulic resistance (pressure drop, ΔP) [11]. A range of such structures (simple cubic lattices, rotated cubes, and designs based on minimal surfaces, among others) have been evaluated as supports with an applied active layer (washcoat). Despite a comparatively low catalyst loading (as in traditional monoliths), regular lattices can markedly intensify operation owing to improved mass/heat transfer. For example, printed aluminum foam-like structures attained the same conversion in Fischer–Tropsch synthesis as a bed of spheres while suppressing hot spots (the reactor operated close to isothermal). The inlet pressure could be kept within acceptable limits by selecting an appropriate cell size [8]. Consequently, printed POCS monoliths are promising for automotive catalytic converters and for processes that require both low ΔP and efficient mass transfer [1].

Heterogeneous static micromixers and reactor inserts. Three-dimensional printing enables catalytic reactors with built-in complex channels and mixing elements. Representative examples include catalytic static mixers—spiral or other inserts in a tube that enhance turbulence and interphase contact—fabricated from catalytic materials or coated with a catalyst (Figure 2b) [9,12]. Nguyen et al. (2018) reported efficient hydrogenation in a tubular microreactor equipped with printed catalytic stirrers, achieving higher selectivity of the target product due to enhanced mixing during flow through such structures [13]. Another option involves microreactors with printed, complex geometry channels whose walls are either catalyst-coated or intrinsically active [14,15]. These devices are used, for example, in fine chemical and pharmaceutical synthesis, where precise residence time control and rapid heat removal are critical [3].

Block catalytic elements for integrated processes. This class comprises unique constructions combining several functions within a single 3D-printed block—for instance, catalyst + sorbent [16], catalyst + membrane [17], or catalyst + heat exchanger [18]. The aim is process intensification via integration of reaction and auxiliary functions. The literature describes multifunctional reactor elements fabricated by AM, for example, a monolith with alternating zones of adsorbent and catalyst to enable simultaneous reaction and removal of a by-product [19] or a metal reactor printed from a catalytic alloy that acts simultaneously as a heater and as the catalyst (a “self-catalytic reactor”) [8]. Although these concepts are still at the research stage, 3D printing provides architectural freedom unattainable by standard assembly methods.

Biocatalytic 3D structures. Additive manufacturing has also been adopted for immobilization of enzymes and cells at the interface of catalysis and biotechnology. Three-dimensionally printed matrices made of biocompatible polymers or hydrogels act as supports onto which enzymes or whole cells are immobilized as the biocatalyst [20]. By prescribing the micro-architecture of pores and channels, one can create an optimal microenvironment for biocatalysis (substrate delivery, product removal, nutrient access). As one example, a microfluidic bioreactor with a printed core module was produced by projection microstereolithography with ≈10 µm resolution, affording high enzyme loading and mechanical robustness at pressures exceeding 130 bar (Figure 2c). Another example is reactors comprising carrier spheres printed from carbon-filled PLA (C-PLA) and chemically modified to immobilize multiple enzymes of different classes; continuous-flow enzymatic syntheses (e.g., lactase reactions, antibiotic formation) were demonstrated on such devices with high enantioselectivity [20]. Thus, AM opens new avenues for flow biocatalysis, enabling individualized multi-enzyme systems.

This classification is not exhaustive—hybrid approaches are possible (e.g., printing small catalytic particles that are subsequently used as a packed bed, or printing an entire reactor with internal catalytic elements). Nevertheless, the categories listed capture the principal directions in which 3D printing is being leveraged to create catalytic structures with enhanced performance.

Differentiating 3D-printed structures by materials, geometries, and functionalization routes illustrates the breadth of current technologies. Classification, however, merely maps this diversity, whereas understanding the historical evolution of form factors reveals how the progression from granules to monoliths and further to triply periodic minimal surface (TPMS) architectures has reframed the role of geometry. The next section examines how perceptions of catalyst architecture have changed and what design principles underpin modern reactor concepts.

3. Evolution of Reactor Form Factors

The historical development of catalytic reactors can be viewed as a continuous pursuit of an optimal balance among active surface area, hydrodynamics, and mechanical robustness. For decades, researchers sought to combine manufacturing simplicity with process efficiency, and changes in support geometry largely determined the outcome. Whereas mid-20th-century designs relied on pellets and simple extrudates, today’s reactor design increasingly employs complex three-dimensional topologies—TPMS and fractal architectures—engineered via CFD and realized by 3D printing. Table 1 compares advantages and disadvantages of different reactor form factors.

Table 1. Comparative characteristics of reactor form factors.

Form Factor	Advantages	Disadvantages	Applications
Pellets	Simple, low-cost manufacturing	High ΔP, stagnant zones, hot spots	Reforming, hydrotreating
Extrudates	Lower ΔP, higher surface-to-volume ratio (S/V)	Limited geometry	Petrochemistry, organic synthesis
Monoliths	Uniform flow, low ΔP	Rigid shape, limited flexibility	Automotive catalysts, emissions control
TPMS	High S/V, low ΔP, tunable architecture	High printing cost, post-processing needs	CO2 methanation, photocatalysis
Fractals/lattices	Multi-scale transport, strength, function integration	Complex design, CAD complexity	Bioreactors, heat exchange, mixing

From pellets to extrudates. Early industrial catalysts were manufactured as tablets, cylinders, or spheres (Figure 3a). These shapes were easy to produce and sufficiently strong for large reactors, but operation revealed serious drawbacks: high pressure drop (ΔP), stagnant zones, hot spots, and flow maldistribution, all of which reduced reactor efficiency and shortened catalyst lifetime [21]. Extrudates (Figure 3b) with holes and channel structures became an attempt to solve these problems. Multi-hole cylinders and Raschig rings were adopted from the mid-1970s as a remedy. These shapes reduced ΔP by approximately 15–20% and increased gas–solid contact area [22]. Even so, extrudates offered limited flexibility: channel geometry was fixed and thus difficult to tailor to a specific process.

Figure 3. Examples of catalyst structures: (a) Example of a granular catalyst [23]; (b) Example of an extruded catalyst [24].

The era of monoliths. Honeycomb ceramic blocks and cermet monoliths marked a step change. By promoting uniform flow and lowering hydraulic resistance, monoliths enabled widespread implementation of automotive catalytic converters and the abatement of industrial emissions [25]. Studies reported a two-to-three-fold decrease in ΔP relative to granular beds while maintaining high activity. Despite these advantages, monolith geometry remained essentially static: channel diameter was fixed, shape variability was limited, and integrating multiple functions within a single block was largely infeasible.

The advent of AM and TPMS. Three-dimensional printing introduced direct control over geometry unconstrained by casting or extrusion. Particular attention has turned to TPMS—low-mean-curvature surfaces such as the gyroid, Schwarz P, and diamond families [26]. TPMS combine high geometric surface area with low ΔP, a regular porous architecture, and fine parametric tunability [27]. For example, Muller et al. (2025) demonstrated that a reactor printed by selective laser melting (SLM) provided higher mass transfer coefficients than conventional monoliths in CO₂ methanation [28]. More broadly, titanium alloy TPMS produced by electron beam melting (EBM) exhibited surface roughness characteristics that surpass those obtained by traditional routes [29]. In addition, structured catalysts produced by direct ink writing (DIW) have achieved higher reaction rates than granular counterparts made from the same material [30].

Fractals and lattice structures. Beyond TPMS, fractal and lattice architectures are rapidly advancing. Fractals enable multi-scale channel networks—from macro- to mesopores—promoting uniform flow distribution and suppressing dead zones [31]. Klumpp et al. investigated how porosity and cell orientation influence ΔP in periodic open cellular structures with ideal cubic geometry [32]. Building on these ideas, fully fractal catalysts have been developed; in one study, the apparent catalytic rate increased by about 70% compared with pelletized beds, while modular sections enabled rapid exchange during operation [33]. Lattices fabricated by selective laser sintering (SLS) or stereolithography (SLA) offer high specific stiffness at low density and can simultaneously function as a catalyst support, heat exchanger, and static mixer [34]. A representative example of multifunctionality is a 316L stainless-steel hybrid reactor in which SLM was used to integrate catalytically active zones (ceria-based washcoat) with heat exchange channels in a single body, leading to significant performance gains [35]. In biocatalysis, fractal polymer scaffolds frequently serve as supports for immobilized enzymes or cells [36,37].

In sum, the evolution of reactor form factors reflects a paradigm shift: geometry is no longer a passive container for the active phase but an instrument for controlling the reactive environment. Today, researchers design the reactor in a computer-aided design (CAD) environment, perform CFD simulations, optimize parameters for the target process, and reproduce the optimized architecture directly on a 3D printer. Geometry has become a determinant of reaction efficiency, mass and heat transfer, and process stability.

The historical trajectory from passive pellets to active architecture became feasible only with the emergence of new manufacturing tools. TPMS geometries and fractal forms cannot be realized by conventional extrusion or casting; AM has made them accessible. The next logical step is to analyze the 3D printing methods that now enable engineering control of catalysts across all relevant length scales.

4. Methods of 3D Printing for Catalytic Structures (ISO/ASTM Classification)

Additive manufacturing encompasses a wide spectrum of processes. The ISO/ASTM 52900 terminology standard distinguishes seven categories of 3D printing methods [38]. Below, these methods are discussed in the context of fabricating catalytic structures, highlighting their specific features, materials, and representative use cases.

In this review, we use the term ‘catalytic hardware’ to denote robust, installable reactor components (monolithic inserts, static mixers, heat-transfer lattices) that simultaneously provide (i) mechanical/thermal functionality in the reactor and (ii) catalytic functionality, either because their surface is later washcoated with an active phase or because the bulk alloy/oxide is itself catalytically active [1,4,39].

Material Extrusion. This category includes the widely used fused deposition modeling (FDM) (also known as fused filament fabrication, FFF (Figure 4a)) and related paste extrusion processes often referred to as DIW or robocasting [40]. In FDM, a thermoplastic filament (e.g., PLA, ABS) is fed through a heated nozzle and deposited layer by layer. DIW dispenses viscoelastic pastes—suspensions of ceramic or metal powders in a liquid binder—through a syringe nozzle [41]. The attainable feature size is governed by nozzle diameter and feedstock rheology: typical track widths are ~200–500 µm for thermoplastics, while specialized micro-extruders can reach ~50–100 µm. Materials include commodity polymers (PLA, ABS), their composites, ceramic pastes (alumina, zirconia, zeolites), and metal-powder-based pastes [42]. In catalysis, oxide-based pastes are common for printing porous alumina monoliths that, after sintering, serve as supports for active metals [43,44,45]; polymer templates may also be pyrolyzed to obtain carbon supports. Post-processing generally involves drying and high-temperature sintering to remove binders and consolidate the body. Advantages include simplicity, low equipment cost, and the ability to produce relatively large parts [46]. Limitations are moderate geometric accuracy (visible layer lines), sintering shrinkage (~20–30% linearly [1]), and tight requirements on paste rheology and drying/sintering schedules to prevent cracking.

Figure 4. Examples of structures produced by various 3D printing methods: (a) an example of a catalyst produced by the FFF method [47]; (b) an example of a catalyst produced by the SLS method [48]; (c) an example of an object produced with high precision using the material jetting method [49]; (d) an example of an object produced by the DED method [50].

Vat Photopolymerization (VP). VP comprises light-driven 3D printing processes in which a photosensitive resin is selectively cured layer by layer—SLA, digital light processing (DLP), and two photon polymerization are representative variants. Objects are formed directly from liquid resin under controlled illumination [51].

The cured VP resin forms a crosslinked polymer network, i.e., a thermoset that cannot be remelted. This is fundamentally different from filament-based material extrusion (FDM/FFF), where thermoplastics such as PLA or ABS are softened and resolidified. In catalysis, VP is therefore typically used either (i) as a route to ceramic or oxide bodies via ceramic-filled or preceramic resins followed by debinding and high-temperature firing [52,53,54], or (ii) to fabricate polymer microreactors (e.g., transparent SLA/DLP channels) that are subsequently functionalized by coating the internal walls with a photocatalyst [20].

Resolution is high: typical layer thicknesses are ~20–100 micrometers, and in-plane-features can reach the tens of micrometers range (specialized systems approach ~5–10 micrometers [10]). For catalytic purposes, one may use neat photopolymers or ceramic-filled resins; for the latter, oxide nanoparticles (e.g., Al₂O₃, ZrO₂) are dispersed in the resin [52]. Printed “green” parts are then heat-treated to burn out organics and sinter the ceramic skeleton [53], enabling intricate ceramic supports (e.g., oxide or zeolite lattices) with high fidelity [54]. Another route prints a polymer lattice subsequently used as a template or as a functional component. Transparent resins have been used to build microreactors with complex channels for photocatalysis by coating channel walls with photocatalysts [20]. VP offers excellent resolution and surface quality and enables delicate internal architectures; constraints include limited build sizes (although they are steadily increasing), resin cost, and removal of uncured resin from tortuous channels.

Powder Bed Fusion (PBF). This family covers laser or electron beam processing of powder layers—selective laser sintering/melting (SLS (Figure 4b)/SLM) and electron beam melting (EBM) [55]. For such catalytic hardware, i.e., load-bearing reactor inserts and monolithic lattices that host an active washcoat or, in specific cases, act as self-catalytic metallic reactors, metal parts are most often produced via SLM under inert gas. With laser spot sizes ~50–100 micrometers and layer thicknesses ~20–50 micrometers, features on the order of a few hundred micrometers are feasible. Materials include stainless steels, Ni- and Ti-based alloys, and, for SLS, selected polymers and composites. Metal AM enables monolithic reactors and heat-conductive supports from Al or Cu for exothermic service, as well as high-temperature Ni-based alloys that are catalytically active themselves (e.g., Ni for hydrogenation, Fe for Fischer–Tropsch) [39]. A “self-catalytic reactor” concept—where the printed metal composition provides catalytic activity—has also been reported [8]. More commonly, inert metallic lattices are printed and subsequently coated with a catalytic layer. For instance, high-temperature alloy lattices were additively manufactured for automotive aftertreatment and washcoated with oxide catalysts; testing showed reduced flow resistance and improved heat management at comparable conversion [1]. Post-processing may include support removal, surface finishing, and stress relief heat treatment. PBF advantages are mechanical robustness, thermal stability, and all-metal architectures that are suitable for harsh conditions (e.g., high-temperature reforming, exhaust systems) [56]. Drawbacks include expensive equipment, high energy consumption, powder constraints (narrow particle size and morphology), and comparatively rough surfaces requiring finishing prior to washcoating [55].

Binder Jetting. In binder jetting, a liquid binder is selectively deposited onto a powder bed to “green bind” the desired shape; loose powder is then removed [57]. The green part is subsequently sintered (ceramics, metals) or infiltrated with a melt. Resolution depends on nozzle/binder droplet size and powder characteristics and is typically ~50–200 µm. A wide range of powders can be handled (metals, oxides, composites). For catalysis, porous cordierite or alumina-based monoliths with arbitrary channel geometry can be printed and then fired to yield ceramic supports [53]. Metal parts can also be produced (e.g., printed steel preforms infiltrated with Cu/bronze), although chemical durability may be system-dependent. Advantages include room-temperature processing, large build volumes, and high throughput; challenges are lengthy post-sintering with shrinkage and mechanical properties that may trail PBF or well consolidated extrusion parts.

Material Jetting. Here, droplets of build material (e.g., photopolymers, salt solutions, colloids) are dispensed and cured or solidified in situ [58]. While primarily a route to high-precision polymer prototypes, research efforts target jetting of catalytic inks (e.g., metal–organic precursors) followed by thermal conversion on preprinted 3D supports [59,60]. In principle, voxel-wise deposition enables gradients or multi-material patterns (zones with different catalysts), though such strategies remain exploratory (Figure 4c). Constraints include narrow viscosity windows for reliable jetting and rapid immobilization of droplets.

Directed Energy Deposition (DED). In DED, powder or wire feedstock is delivered into a focused energy beam (laser, electron beam, or plasma) and melted onto a substrate, building up material additively (Figure 4d) [61]. Functionally akin to “3D welding,” DED is used for repair, cladding, and large metal components [62]. Its use in catalysis is nascent, but it could deposit catalytic overlays directly onto reactor walls or lattices, forming metallic catalysts in situ without pressing or firing steps. Benefits include high deposition rates; limitations are coarse geometric resolution (millimeter scale) and significant thermal stresses.

Sheet Lamination. Thin sheets are bonded—by adhesive or welding—and contoured to form the part (e.g., laminated object manufacturing, LOM) [63]. Owing to difficulties in creating intricate internal channels, this route is seldom used in catalytic applications, though stacked, micro-etched foils for certain reactor inserts are conceptually possible. In practice, freeform AM methods are more effective for complex 3D architectures; sheet lamination is noted here for completeness only.

It is worth noting that multiple AM methods can be combined in a single device (hybrid AM). For example, a reactor shell may be produced by PBF, while an internal ceramic insert is extruded by DIW. In most projects, however, one method is selected and both material formulation and geometry are optimized accordingly. Table 2 compiles key characteristics of major 3D printing methods for catalytic structures.

Table 2. Comparison of principal AM methods for catalytic structures.

Method (ISO/ASTM)	Resolution (Order of Magnitude)	Materials	Representative Catalytic Applications
Material Extrusion (paste or filament)	~200–500 µm (track/layer); improved setups to ~100 µm	PLA [64], ABS [65]; ceramic pastes [66] (Al2O3, zeolites); composites [67]	Porous alumina supports (honeycombs, grids) followed by sintering, carbon monoliths via pyrolysis of printed polymer preforms [30,42,43].
Vat Photopolymerization (SLA/DLP)	~20–100 µm (vertical); ≤~50 µm in-plane	Photopolymers [68]; nanocomposites [69] (resin + ceramic powder)	Thin-walled lattices from ceramic-filled resins with subsequent firing, microreactors with microchannels for photocatalysis, etc. [20,52,53,54].
Powder Bed Fusion (SLM/EBM)	~50–100 µm (laser spot); 20–50 µm layers	Metals [70,71,72] (steel, Ni- and Ti-based alloys); selected polymers [73] (SLS)	Structured nanoporous copper catalysts for on-board methanol steam reforming, printing catalysts from reactive alloys (e.g., Ni-containing) for hydrogenation, etc. [74].
Binder Jetting	~100 µm (powder-dependent)	Ceramic powders [75] (Al2O3, ZrO2); metals [76,77] (steel, Inconel)	Complex ceramic monoliths with subsequent calcination, porous metal parts with post-infiltration and catalytic functionalization, etc. [53].
Material Jetting	~50–100 µm (droplets)	Photopolymers [78]; catalytic inks [59,60] (salt solutions, colloids)	Prototyping of micro-devices, experimental graded catalytic coatings (lab-scale).
Directed Energy Deposition	>500 µm (coarse)	Metal wire [79] or powder [80]	Cladding catalytic layers onto heat-exchange tubes (concept), repair/modification of catalytic meshes.
Sheet Lamination	~100 µm (sheet-thickness-limited)	Metal foils [81], films [82]	Rarely used, potential for stacked micro-mixers or foil-based catalysts.

Note: Resolution values are indicative; actual performance depends on equipment and materials. Application examples are drawn from the 2015–2023 literature.

As the table suggests, each method occupies a distinct niche. Paste extrusion (DIW) is favored for oxide supports owing to simplicity and scalability; VP excels in high-precision microstructures; and PBF is the method of choice for robust metallic catalysts requiring thermal stability. Selection of a printing route for a given catalytic task considers feedstock compatibility (e.g., zeolites with DIW, stainless steel with SLM), target feature size/tolerance, and techno-economics (throughput, feedstock cost).

AM technologies continue to evolve. Hybrid systems (e.g., VP combined with particulate injection) are emerging, and new “green” formulations—including bio-derived or renewable polymer inks—are being developed to support sustainable manufacturing of catalytic bodies [20]. Ultimately, the printing step is only the beginning: post-processing, surface modification, and incorporation of active phases transform a printed preform into a functional catalyst. The next section examines materials and functionalization strategies in detail.

5. Materials and Feedstocks for 3D-Printed Catalysts

The choice of material is a key design lever in the development of a 3D-printed catalyst. The material dictates the printing and post-processing window as well as the ultimate catalytic properties (chemical stability, nature of active sites, porosity, etc.). In practice, two broad classes are used:

• Supports (inert substrates) that are subsequently loaded with an active component;
• Catalytically active materials that directly perform the target reaction.

Below, we survey the principal material categories used in additive manufacturing of catalytic structures.

Ceramic oxide materials. Conventional catalytic supports—alumina (γ Al₂O₃), silica (SiO₂), zeolites, mullite, cordierite, zirconia, and others—have also been adapted for 3D printing. This oxide family also includes amorphous silica–alumina (ASA) and related mixed SiO₂/Al₂O₃ supports that are widely used as thermally robust acidic supports, particularly in high-temperature hydrocracking (HC). From the AM standpoint, ASA-type mixed oxides fall under the same ‘printable ceramic paste/binder-containing green body → debinding → high-temperature sintering’ workflow that we describe for alumina and zeolites [43,44,45,83,84]. In practice, silica–alumina or silica–alumina–zeolite slurries can be extruded by DIW or shaped by binder jetting, then calcined to yield a porous, acid-functional monolith suitable for high-temperature refinery service. Thus, ASA should be viewed not as a separate category but as part of the printable ceramic/mixed-oxide supports portfolio critical for HC and useful in selected hydrotreating (HDT) duties where acidity mainly tunes support properties (e.g., dispersion, isomerization).

Conventional catalytic supports are typically employed as powders (micro- or nanoscale) formulated into printable pastes for DIW or into photocurable suspensions for SLA, or they are spread as loose powders for binder jetting. For example, alumina—one of the most widely used supports—has been printed by FDM as a composite in which Al₂O₃ powder (~50–60 wt.%) is blended with a thermoplastic binder to produce a filament. After printing, the “green” body undergoes polymer removal and sintering at ~1500 °C, yielding a robust porous oxide monolith [83]. Analogously, zeolites (crystalline aluminosilicates) can be shaped by 3D paste extrusion followed by calcination [43]. The principal challenge for ceramics is the substantial sintering shrinkage and the risk of cracking; plastic binders, glass frits, and step-wise heating schedules are therefore used to control densification [84]. Even so, the printed ceramics retain the advantages of conventional supports—thermal stability, tunable pore networks (after appropriate processing), and chemical inertness—and they can be activated by standard routes: impregnation with metal precursors, ion exchange, deposition, etc.

Metals and alloys. Metallic materials in catalyst printing are used in two ways: (i) as mechanically strong, thermally conductive structures that are later coated with a catalytically active layer; and (ii) as the catalyst itself (when the metal is catalytically active). An example of the first case is a lattice block in 316L stainless steel produced by SLM and subsequently coated with ceria and noble metals for automotive exhaust aftertreatment [35]. As to the second, nickel-based alloys are inherently active in many reactions (hydrogenation, CO₂ methanation, steam reforming). By printing a porous architecture in a Ni-based alloy (e.g., Inconel or Ni–Cr–Al), one obtains a monolithic catalyst that may require no additional loading. A “self-catalytic reactor” has been described in which a metallic lattice printed from a Ni/Al-containing alloy forms a dispersed NiO/Al₂O₃ surface after oxidative annealing, active in the target reaction [8]. Precious metals are costly, yet small catalytic elements can be produced directly—for instance, selective laser sintering of Pd/CeO₂ powder has been reported for Suzuki–Miyaura coupling [85]—although, in most cases, noble metals are deposited onto printed supports by conventional methods (e.g., impregnation with Pt or Pd salts followed by reduction). Metallic carriers based on aluminum or copper are also attractive for highly exo- or endothermic processes due to their thermal conductivity; printed aluminum foams, for example, effectively remove heat and suppress hot spots [86]. After printing, surface treatments such as etching or grit blasting are sometimes applied to improve adhesion of the catalytic coating [3].

Polymeric materials. Thermoplastics (PLA, ABS, nylon, etc.) are ubiquitous in 3D prototyping but see limited direct use in high-temperature catalysis. Nevertheless, polymeric prints are valuable auxiliary tools. First, complex supports and grids can be printed from plastics and subsequently functionalized at low temperature—for example, with metal–organic frameworks (MOFs). Pellejero et al. demonstrated an ABS filter whose surface was overgrown with MOF crystals (Cu₃(BTC)₂); the resulting structure effectively captured and decomposed toxic gases [87]. Here, the polymer acts as a lightweight scaffold with prescribed pore geometry, while the MOF provides adsorption/catalytic function. Second, polymers can serve as sacrificial templates: a printed polymeric lattice can be calcined to leave porosity in an infiltrated matrix or carbonized to yield a porous carbon replica used as a catalytic adsorbent. This strategy underpins the fabrication of carbon monoliths that support platinum group metals for automotive catalysis. There is also a growing set of specialty resins for catalysis, including preceramic polymers that convert to ceramics upon heating [88]. Biopolymers such as PLA are proposed for disposable, single-use enzyme cartridges in line with “green chemistry” and sustainability goals.

Composite and hybrid materials. Combining constituents often gives the best results. Polymer–particle composites for 3D printing are actively pursued—for instance, filaments in which a polymer matrix immobilizes a catalytic powder. A PLA filament containing Fe₂O₃ has been used to print a lattice that operates as a heterogeneous Fenton catalyst for water treatment; after several cycles, activity decreased only slightly, while mechanical strength enabled easy retrieval and reuse [89]. Another route is catalytic inks for material jetting: suspensions of palladium nanoparticles in a solvent can be patterned on 3D surfaces or printed as standalone motifs [90], although volumetric porosity is difficult to control this way. Of particular interest are MOF-based composites, such as printable pastes in which MOF particles are mixed with a polymer or clay. After shaping and thermal treatment, porous monoliths that preserve the MOF structure are obtained—promising for catalytic detoxification or energy-efficient adsorption processes [53,91].

A practically important subset of such composites for refinery service are mixed supports (e.g., silica–alumina blended with zeolites or alumina), where multiple phases are co-printed to combine mechanical strength, Brønsted acidity, and diffusion control. These mixed-oxide/zeolite systems are directly relevant to HC (acid-catalyzed) and to selected HDT operations where support acidity and hierarchical porosity aid isomerization and mass transport within a single printed monolith, rather than relying on separately extruded pellets.

Biomaterials. Enzymatic 3D printing relies on hydrogels (alginate, gelatin methacrylate, etc.) that cure under UV light or via chemical crosslinking. These matrices permit printing of soft, water-rich scaffolds into which biocatalysts (enzymes) can be immobilized without loss of activity. Operating under mild conditions (ambient temperature, aqueous media), such systems are relevant to biomedical synthesis and to food and pharmaceutical processing. As an example, a printed pH-responsive hydrogel with immobilized glucose oxidase was used in a micro-bioreactor for controlled glucose oxidation [20]. Although a niche today, biomaterials highlight the breadth of additive approaches across catalysis.

In summary, selecting a material for a 3D-printed catalyst entails a tradeoff between printability and the functional requirements of the catalytic duty. There is no universal choice: each “method–material–reaction” combination must be optimized. That said, the printable materials library has been expanding rapidly and already spans key needs—from refractory oxides for refinery service to biodegradable polymers for “green” synthesis.

6. Post-Processing and Strengthening of Printed Structures

After completion of 3D printing, the catalytic structure typically requires post-processing before use in a reactor. The specific steps depend on the printing technology and material but generally include the following:

Removal of binders and consolidation (debinding and sintering). For most ceramic and metallic parts printed with polymeric binders (pastes, photopolymers, or binder in binder jetting), a controlled thermal schedule is essential: a low-temperature stage (100–500 °C) to burn out organics (with the maximum gas release rate near the polymer decomposition temperature), followed by high-temperature firing (≈1000–1500 °C) to sinter the inorganic skeleton. Heating rates and dwell times are tuned to avoid defects. Shrinkage is unavoidable: volumetric changes during oxide sintering may reach 30% [1], which must be accounted for in the design (oversizing at the printing stage). Uniform, gradual binder removal is critical to prevent cracking caused by pressure buildup in closed pores. For mixed oxide carriers such as ASA and silica–alumina–zeolite blends, binder content is a double-edged tool: while it provides green strength for printing, excess organics dilute acid sites and can partially block meso-/micropores. Aggressive burnout can also introduce internal stress, leading to microcracks or collapse of thin struts [83,84,92,93]. Binder-lean (‘binderless’) shaping routes are therefore actively explored to preserve catalytic acidity and diffusional accessibility [92,94]. In metal–polymer systems (e.g., FDM), debinding is often followed by infiltration or high-vacuum sintering to densify the body [95].

Thermal treatment of the active phase. If the active catalytic component is incorporated into the printable feedstock (e.g., a paste containing a metal salt), post-processing includes thermal decomposition of the precursor into the active phase. For instance, for a “Ni salt + resin” composite, calcination in a reducing atmosphere is required to form Ni nanoparticles on the support [96]. Calcination is also performed after impregnation of printed supports: the monolith impregnated with a metal salt is dried and heated (typically 300–500 °C) to generate the oxide or metallic active phase in situ [97].

Mechanical finishing and cleaning. Printed parts may contain sacrificial supports or flash, especially after PBF and DED. These features are removed (cutting or breaking), and surfaces are ground or sand-blasted if needed. For example, metal lattices printed by SLM are often subjected to abrasive finishing to remove spatter and reduce a ~10–50 µm roughness, promoting uniform coating deposition. Residual loose powder must be cleared from internal channels—by air purge or vibration—prior to sintering in binder jetting or SLS. These finishing steps are not cosmetic: controlled roughening (grit blasting, etching) improves washcoat adhesion on metallic lattices [3], while careful edge grinding after sintering ensures dimensional fit of brittle oxide/ASA monoliths and removes surface skin that could hinder uniform flow distribution (see also Section 8 on tomographic inspection of blocked channels).

Annealing and quenching. Printed metal catalysts frequently undergo stress relief annealing to adjust the microstructure and eliminate residual stresses. For example, as-printed Inconel [34] may contain residual stress; annealing at ~800 °C mitigates brittleness. In some cases, a controlled anneal in a reactive atmosphere is used to form an active surface: as noted earlier, Ni–Al alloys can be air annealed to grow a catalytically active nickel oxide layer [98,99].

Impregnation and activation (as part of functionalization; detailed below). Strictly speaking, deposition of the active phase is also post-processing for support. Standard approaches are used—solution impregnation, chemical/gas phase deposition—and then drying, calcination, and reduction (e.g., H₂ for metal–oxide systems) are used to activate the catalyst. For printed bodies, these stages mirror those used for conventional pellets.

Geometry verification and firing fit adjustment. Upon completion of thermal treatments, dimensional and shape control is often performed. Minor distortions—typical of larger parts—can be removed by edge grinding to ensure proper seating in the reactor and flat end faces. For instance, a printed cylindrical monolith is slightly lapped at the rims before inserting into a tubular reactor to avoid gaps or stress concentrators.

It bears emphasizing that post-processing influences the final catalyst properties no less than the printing step itself. In particular, the sintering schedule governs residual porosity, strength, and accessible surface area. Studies indicate that excessively aggressive sintering can seal a portion of the pore network or trigger deleterious phase transformations, reducing activity [92]. Conversely, insufficient sintering leaves poor mechanical integrity and a risk of in situ fragmentation. Consequently, a compromise is optimized: sinter just enough for strength while preserving a target fraction of porosity and the integrity of active components.

Debinding as a distinct challenge. Gaseous products of binder decomposition must diffuse out without causing “pore bursts.” A stepwise protocol is often adopted: a hold at 200–300 °C (removal of volatiles), then a ramp to 400–500 °C (breakdown of the residuals), and only thereafter a firing above 1000 °C. This approach has been used, for example, for printed zeolite blocks containing ~20% organic binder [93].

Post-processing of metals beyond heat treatment: chemical routes. Some printed metal catalysts are deliberately corroded (etched) to increase roughness or generate porosity. For instance, a Cu-containing steel alloy can be etched to selectively dissolve copper, creating nanopores on the surface and increasing the interfacial area available to reactants.

In sum, post-processing is an integral stage in the technology of 3D-printed catalysts. It demands an interdisciplinary perspective spanning materials science (sintering kinetics, binder removal), chemical engineering (precursor decomposition), and mechanical engineering (heat treatment of metals). A properly engineered post-processing route turns printed performance into a fully functional industrial catalyst that meets strength, stability, and activity requirements.

7. Methodologies for Functionalization of Printed Structures

Once a 3D-printed support (carrier) has been fabricated and consolidated, the next step is to impart catalytic functionality, i.e., to introduce the active components. Depending on the design, functionalization can be performed prior to printing (the material being printed is already catalytically active) or after printing (an inert form is printed and subsequently activated).

Below, we overlook the main approaches, such as direct printing of catalytic material, deposition of active components onto a printed support, and multi-material printing.

• Direct printing of a catalytic material.

Metal–ceramic printing. A powder of an active catalyst (e.g., Ni or a Co-containing alloy) is mixed with a ceramic support to form a paste. After printing and firing, particles of the active metal are distributed throughout the structure [100]. However, the high sintering temperature may cause agglomeration of metal particles and loss of activity. Direct incorporation is therefore reasonable only if the active component tolerates sintering or can be activated afterwards. For zeolite catalysts (where the acidic catalytic center is part of the zeolite framework), the printed and fired body is already a functioning catalyst.

Printing from a precursor. “Inks” are solutions or gels that yield the catalyst upon heating. For example, a salt solution containing Cu and Al can be pattern-printed by inkjet on a substrate; after calcination, CuO/Al₂O₃ spots are obtained—although this is poorly suited to bulk structures. A more effective route uses photopolymer resins with dissolved metal complexes. After curing the resin and firing in an inert atmosphere, a finely dispersed metal remains on a carbon matrix (polymer → carbon). Kotz et al. (2019) formulated a photopolymer that included organometallic complexes, enabling direct printing of catalytically active structures bearing functional groups [101].

“Nanocatalyst carpet.” In this variant, the support is printed while the active component is generated chemically during printing. For example, in electrochemical 3D printing, catalytically active ferromagnetic nanoparticles were electrodeposited in situ onto a printed hydrogel substrate during the printing step [102]. This direction remains at the laboratory stage.

2.

Deposition of active components onto a printed support (post functionalization).

Impregnation from solution. A printed porous monolith is immersed in a solution of a precursor of the active metal (e.g., nitrate or acetate), allowed to penetrate the pore network, removed, drained, and dried. Calcination then forms the oxide; a subsequent reduction step is applied when a metallic phase is required. This mature method readily introduces multiple components sequentially. The drawback is possible nonuniform uptake in large monoliths. Even so, successful cases exist: Johnson Matthey reported a 3D-printed ceramic support impregnated with a proprietary catalyst that achieved complete conversion of squalene to squalane with high yield [103].

Coating (washcoating). Widely used for honeycomb monoliths, a suspension of catalytic powder is deposited onto channel walls. The same approach works for 3D-printed lattices: a suspension (e.g., a zeolite powder with Pt) is applied by immersion or brushing, followed by drying and calcination. Studies indicate that regular printed lattices can retain the washcoat effectively when the slurry viscosity is properly tuned. The coating thickness is limited to avoid pore blockage, so the overall mass loading is usually modest [94]; this is compensated by geometry-enabled intensification and more effective utilization of active sites.

Chemical deposition (CVD, ALD). Gas-phase deposition (chemical vapor deposition, CVD) and atomic layer deposition (ALD) allow for very uniform thin coatings over the entire internal surface of complex 3D structures. ALD is particularly attractive: for instance, a monolayer of TiO₂ can be deposited throughout a printed porous lattice to create a photocatalytically active skin. Conversely, a conformal carbon layer can be grown to tune surface acidity. There are also reports of ALD-based functionalization of metallic 3D-printed reactors with MOF films: vapor-phase growth of UiO 66 on a printed metal substrate increased the specific surface area and endowed adsorption functionality [8,104].

Growth of nanostructures on the support. Here, active nanostructures are formed directly on the printed carrier. A representative example is MOF growth: a porous (polymer or ceramic) structure is immersed in the appropriate reagents, and an MOF crystallizes on the framework under hydrothermal conditions. Mullite lattices functionalized with HKUST 1 have been reported for selective catalysis [53]. Carbon nanotubes, metal nanoparticles, and similar structures can likewise be grown on the printed scaffold.

Immobilization of enzymes and other biocomponents. In biocatalytic systems, mild chemistry is required: a printed hydrogel is impregnated with an enzyme solution, and the enzyme is either physically adsorbed or covalently anchored to the matrix (e.g., via a polydopamine interlayer). After washing off unbound protein, an enzyme-loaded reactor is obtained. Ye et al. described a versatile procedure in which a PLA (polylactide) scaffold was coated with polydopamine to immobilize diverse enzymes (penicillinase, lipase, etc.) while preserving their activity [20].

3.

Multi-material printing (co printing). A promising direction is the simultaneous printing of the support and the active phase on multi-material printers. In two-extruder printing, one extruder lays down a ceramic support while the second dispenses a catalyst-containing paste, producing zones enriched with the active component. In SLA, two resins can be alternated: an inert resin and a second resin bearing, for example, an acid precursor to create acidic sites. Although still experimental, such approaches have been demonstrated. Lawson et al. (2021) noted the feasibility of gradient printing of porous structures, with the active component concentration varying layer by layer to optimize activity profiles along the reactor [16]. Multi-material strategies also encompass printing catalytic membranes within a structure or co-printing sensors with the catalyst for online monitoring.

The choice of functionalization strategy depends on process chemistry and the required stability. For automotive three-way catalysis, a robust coating on an inert support is preferred—thus a washcoat followed by strong oxide anchoring during calcination. For continuous liquid-phase synthesis, impregnation is feasible provided the monolith is not excessively long and uniform uptake can be achieved. For micro-bioreactors, gentle enzyme immobilization is essential to avoid denaturation.

It is worth emphasizing that additive-manufactured carriers can sometimes be functionalized more rationally than conventional supports. For example, a regular 3D lattice may include designed “wells” or channels to guide impregnating solutions, improving spatial uniformity of the active phase. Moreover, a printed monolith is typically handled as a single piece, enabling repeated impregnation/washing cycles without the mechanical losses characteristic of packed pellets.

Some functionalization routes are protected by patents. BASF’s X3D technology covers not only catalyst geometry but also a specific method of applying the active phase to penetrate deep into complex structures [4]. Russian patent RU 2734425 C2 claims an end-to-end workflow: pellet shape modeling, 3D printing, impregnation with metal salts, and controlled conversion to oxides [2].

In summary, functionalization is the decisive step that converts a printed “blank” into an operational catalyst. While broadly analogous to treatments used for conventional supports, it must account for additive specific features such as scale, internal channels, and possible anisotropy; a well-chosen protocol unlocks the performance potential inherent to the printed geometry.

8. Structural Characterization of Printed Catalytic Systems

Additively manufactured catalysts differ from conventional pellets or extrudates in two crucial ways: (i) they contain deliberately engineered, millimeter- to micrometer-scale 3D channel networks that must match the CAD design to deliver the targeted pressure drop (ΔP), heat transfer, and residence time distribution; and (ii) they are often monolithic ‘catalytic hardware’ pieces rather than loose pellets, so mechanical integrity, washcoat adhesion, and absence of blocked channels directly determine reactor uptime. Therefore, characterization (‘metrology’) is not a generic QA step but a dedicated qualification workflow that links printing (Section 4 and Section 5), post-processing and debinding/sintering (Section 6), functionalization (Section 7), and reactor design/performance (Section 9 and Section 10). In this section, we summarize the specific methods used to qualify 3D-printed catalysts and explain why they are chosen.

Three-dimensional scanning and tomography. X-ray microcomputed tomography (micro-CT [105,106]) enables nondestructive 3D imaging of the internal architecture with micrometer-scale resolution. For printed catalysts, micro-CT is essential because it nondestructively verifies internal channels, compares as-built geometry to the CAD model (capturing anisotropic shrinkage from debinding/sintering), and detects blocked passages or binder-related cracks that would be invisible in a conventional pellet [4,105,106]. For printed catalysts, micro-CT is used for the following:

Measuring the actual channel dimensions, wall thickness, and unit cell geometry and comparing them with the CAD model—essential for accounting for sintering shrinkage and detecting distortions.

Identifying defects such as cracks, blocked channels (e.g., due to residual powder), and gas evolution voids. Micro CT often reveals microcracks invisible to the naked eye, prompting either rejection or process correction [4].

Evaluating coating uniformity when constituents differ in X-ray attenuation; for instance, a platinum-containing washcoat on a ceramic substrate can appear as a thin internal film.

Optical and electron microscopy. Scanning electron microscopy (SEM) is used for the following:

Examining the surface microstructure and layer topology (e.g., staircase features of layerwise fabrication), sintering induced roughness, and pore distribution. In extruded bodies, SEM reveals binder-derived pores between large support particles [92].

Mapping the size and distribution of active phases by SEM–EDX (energy-dispersive X-ray spectroscopy), verifying penetration into the pore network versus preferential deposition near the external surface—critical for thick monoliths.

SEM is also applied to inspect coking or wear after testing and checking for channel blockage. For example, in a 3D-printed methanation reactor, extended operation led to uniform carbon coverage without local clogging, indicating well distributed flow.

Porous structure analysis (adsorptive methods). Although printed structures feature regular macropores (millimeter-scale channels), the base material is commonly meso-/microporous. Characterization includes the following:

N₂ adsorption–desorption isotherms analyzed by Brunauer–Emmett–Teller (BET) for specific surface area (m² g⁻¹) and by Barrett–Joyner–Halenda (BJH) for pore size distribution. Comparing the starting powder with the sintered monolith typically shows a decrease in BET area [92].

Mercury intrusion porosimetry to quantify macropore distributions (≈0.1–100 μm) and the effects of pore formers.

Permeability and pressure drop (ΔP) measurements. Unlike conventional packed beds, where ΔP is mostly dictated by the particle size distribution, AM lattices are designed to deliver a target ΔP at a given void fraction. Measuring ΔP across a printed monolith thus becomes a primary performance metric, on par with catalytic conversion [1,4]. By flowing a gas or liquid through the sample at controlled flow rates and measuring ΔP, the effective permeability can be estimated (e.g., via Darcy or Ergun correlations). Regular printed lattices have shown ≈2–3× lower friction factors than random packings at comparable bed porosity [4].

Phase and chemical analysis. X-ray diffraction (XRD) is used to confirm active phase formation (e.g., metal after reduction) and to check that printing/sintering did not induce unwanted phase transformations in the support. Scherrer analysis of Ni peak broadening provides mean crystallite sizes.

X-ray photoelectron spectroscopy (XPS) is used for surface oxidation states and to detect residues from binders (e.g., carbon/silicon from photopolymers). Proper calcination generally removes polymeric residues to below detection limits [1].

Transmission electron microscopy (TEM) is used to directly observe nanoparticle size and dispersion; for instance, Pd nanoparticles of ~10 nm stabilized by a carbon matrix after printing/pyrolysis of a PLA based composite.

Elemental analysis (ICP–OES and EDX). Given the larger monolith mass, ICP–OES provides accurate metal loadings (e.g., Pt 1 wt.%, Ni 5 wt.%). EDX mapping across cross-sections checks for undesirable concentration gradients.

Mechanical testing. Because AM catalysts are often installed as single monolithic inserts rather than loose pellets, compressive/flexural strength and thermal shock resistance must be benchmarked against reactor handling conditions and cycling; this differs from classical crush-strength tests on individual pellets [1]. Optimized sintering has yielded Al₂O₃ lattice monoliths capable of supporting human body weight without failure—evidence of high mechanical robustness [4].

Thermal stability and cyclic durability. Thermal shock and thermal cycling tests (e.g., 500–800 °C) identify weak interfaces; monolithic lattices shed less dust and suffer less attrition than packed beds [1].

Catalytic testing. Activity/selectivity in a model reaction (e.g., CO oxidation, liquid phase hydrogenation) relative to granular analogs; printed bodies often match or surpass conversion at lower ΔP [4].

Lifetime and deactivation. Flow and thermal uniformity in printed architectures can suppress localized coking; in Fischer–Tropsch service, a printed metallic insert improved temperature uniformity and mitigated carbon deposition, extending catalyst life [107].

Overall, comprehensive characterization—augmented by tomographic inspection of geometry and mechanical integrity—ensures predictable, efficient operation of 3D-printed catalysts. These data clarify which features are critical (e.g., binder effects that dilute activity, motivating binderless routes) and confirm that rational lattice design delivers the flow optimization predicted by simulations [4]. Characterization informs geometry and hydrodynamics in the next stage: computer-aided design with CFD-guided optimization and multi-scale modeling, linking analytical tools to the practical creation of working reactors. In other words, Section 8 provides the qualification toolkit that closes the loop between geometry (CFD-driven design in Section 9), manufacturability and post-processing (Section 6), and catalytic duty. Such a dedicated metrology stage is specific to 3D-printed catalytic hardware and would be unnecessary for conventional extrudates, where channel topology and ΔP emerge from random packing rather than from an engineered architecture [1,4].

9. Design of Catalytic Structure Geometry

One of the principal benefits of 3D printing is the freedom of geometrical design. That freedom must be used judiciously; to deliver tangible gains (e.g., lower pressure drop or the elimination of hot spots), the structure must be engineered for the target process. This section outlines how 3D-printed catalysts are designed, what computational tools are employed, and which design concepts underpin the geometry.

Flow and reaction modeling (CFD, hydrodynamics). Design typically begins by setting a target, e.g., “reduce the pressure drop while maintaining a geometric surface area of at least X m²·m⁻³ and sufficient mass transfer performance.” CFD and reaction engineering are then used to evaluate candidate geometries. The unit cell of a lattice or the channel of a porous monolith is modeled, and CFD yields distributions of velocity, pressure, and heat transfer and mass transfer coefficients for the specified cell geometry (e.g., square vs. circular vs. triangular channels; lattices with different wall inclinations). Dimensionless performance criteria—such as the Sherwood (Sh) and Nusselt (Nu) numbers versus the Reynolds number (Re)—are computed, and flow resistance is evaluated (e.g., via the Ergun framework).

Pseudo-homogeneous reaction modeling. In some cases, intrinsic kinetics are coupled directly to the CFD to predict axial profiles of conversion and selectivity. For processes sensitive to residence time distribution, contrasting channel designs can be compared—for instance, a helical channel that approaches plug flow behavior versus a straight channel that tends toward mixed flow. As an illustration, Kramer et al. (2018) modeled flow in an ABS prototype of a steam-reforming reactor with optimized channels and showed improved selectivity due to the removal of stagnant zones [18].

Topology optimization. More advanced workflows use algorithms that “discover” shapes subject to constraints. A typical objective is to maximize surface area under a bound on ΔP. The resulting shapes—often featuring through holes and grooves—can then be realized by additive manufacturing. Notably, the BASF Quattro (a four-lobed star extrudate) benefitted from such optimization and was later evolved into the X3D architecture [4].

Unit cell design and scale-up. Many structures (e.g., honeycombs, POCS) are defined by a periodically repeated unit cell. The designer selects the cell type (cubic, tetrahedral, rhombic dodecahedral, or triply periodic minimal surfaces, TPMS, such as gyroid/Schwarz P/diamond) and then tunes parameters—cell size, wall thickness, and wall inclination—which control the following:

• Void fraction (porosity) of the overall body, affecting volumetric catalyst loading and residence time;
• Geometric surface area per unit volume, a key metric to be maximized. Three-dimensional printing can deliver ~150% of the surface area of standard shapes without a commensurate increase in flow resistance [4];
• Channel cross-section curvature and boundary shape, which influence flow regime (rounded sections limit recirculation/stagnation; sharp features can increase mixing);
• Channel density (cells per square inch, cpsi) in monolithic structures. While 3D printing allows for graded or nonuniform channels, uniform cpsi is often chosen for flow uniformity. Densities comparable to automotive substrates (≈200–600 cpsi) and ≈300 cpsi have been achieved, with higher wall porosity than typical ceramics.

Virtual prototyping. After narrowing down candidate designs, a CAD model is prepared, and the build file (sliced model) is generated. Prior to printing, virtual simulations are often performed:

• Sintering deformation analysis (e.g., in Abaqus/ANSYS) to anticipate shrinkage and adjust scale factors;
• Structural integrity analysis by the finite element method (FEM) to identify failure pressures/loads; if insufficient, support struts or stiffeners are introduced. In the X3D program, among seven evaluated shapes, the one combining the largest surface with acceptable mechanical robustness was selected; several exotic forms proved brittle in testing [4];
• Scale-up assessment on multi-cell domains to capture cross-sectional maldistribution in larger monoliths. Graded structures (e.g., smaller cells near the perimeter) can compensate for lower edge velocities. Axial or radial gradation in porosity (e.g., 50% → 80% along the length) has been proposed and realized to offset changes in reactant concentration [1].

Manufacturability constraints. Practical limits of the printing process are embedded early in the design:

• Minimum radius, wall thickness, and allowable overhang (to avoid unsupported spans). For SLA/DLP, ligaments <50 µm may not cure reliably; in extrusion-based DIW/FDM, “printing in air” is avoided by orientation or supports;
• Shrinkage compensation, often ~1.2–1.3× for ceramics; anisotropic shrinkage can be pre-compensated when known;
• Assembly tolerances, especially for inserts into housings; small clearances are reserved to accommodate thermal expansion and to prevent binding or cracking during operation.

A case example is BASF’s X3D catalyst. BASF aimed to reduce ΔP in contact beds for SO₂ oxidation while maintaining or improving activity. Traditional four-lobed “star” extrudates were benchmarked against seven 3D-printable geometries (with internal voids and curved channels) identified by CFD and surface area analysis. “Shape #7” exhibited a 66% lower theoretical ΔP and a 15% larger surface relative to the best extruded Quattro [4]. When printed from the catalyst formulation (V₂O₅ on a support) and field-tested, the X3D bed cut the layer resistance by ~75% and increased plant throughput; the SO₂ conversion rose by ~1.3% (≈97.7% → ≈99%) due to improved diffusion and more uniform gas distribution [4]. This outcome was enabled by design for additive manufacture and would not be feasible with conventional extrusion.

Non-conventional design strategies. Several unconventional concepts are being explored:

• Flow-aware grading. If axial concentration profiles are known, spatially varying density can be imposed: a denser entry section (more active sites) followed by a more open exit section (lower ΔP where reaction nears equilibrium). Voxel-level control in AM facilitates such grading.
• Integrated ribs and swirl promoters. Small internal features (e.g., spirals) intensify local mixing. Additive methods can embed these within channels without interruptions; size and pitch are optimized to balance mixing gains against ΔP penalties.
• Hierarchical porosity. Macro-channels (millimeter scale) are combined with meso-scale passages (10–100 µm), e.g., micro-grooves on channel walls. Such secondary porosity enhances intra-wall diffusion. Approaches include post-printing laser texturing or direct printing at finer resolution.

Generative design software. Dedicated tools (e.g., Autodesk Within, nTopology) accept performance targets (mechanical strength, pressure drop, thermal transfer) and generate lattice architectures automatically. In static mixers, generative designs have yielded bio-inspired shapes that outperform classic Kenics geometries at comparable ΔP.

In summary, the design of 3D-printed catalysts is inherently interdisciplinary, combining reaction engineering, CFD, and materials science. With CFD and topology optimization, a “sweet spot” can be identified, where a printed structure surpasses traditional shapes. As noted by Rosseau et al., this sweet-spot region—moderate catalyst loading at low ΔP—is difficult to reach with extrudates [1]. Continued advances in computation and algorithms will likely automate much of the design space exploration, leaving the engineer to validate the best candidate and dispatch it to the printer. Contemporary reactor design based on 3D-printed architectures enables, in practice, advantages unattainable with granular beds—namely, improved mass transfer, controlled hydrodynamics, and function integration. It is therefore natural to proceed to an analysis of the key advantages that make 3D-printed catalytic structures promising for industrial deployment.

10. Advantages of 3D-Printed Catalytic Structures

The adoption of additive manufacturing in catalysis is driven by the need to overcome the limitations of conventional catalyst shapes. The key advantages of 3D-printed structures can be grouped into technical (process performance) benefits and economic/operational benefits. The principal points are substantiated below:

Enhanced mass transfer performance and apparent reactivity. Owing to deliberately engineered geometry, printed structures can provide extensive interfacial area between reactants and the catalyst while concurrently reducing diffusion barriers. In conventional packed beds, a non-negligible fraction of the active phase may remain underutilized due to intraparticle diffusion limitations (Thiele modulus effect) [1]. In printed pellets featuring internal channels or in thin-walled lattices, the effective diffusion path is shorter, which increases the observed catalytic rate. For example, pellets with radial channels enabled the reaction to proceed across the entire pellet volume, whereas conversion in solid extrudates was restricted to a surface layer [2]. In Johnson Matthey’s (2019) hydrotreatment of squalene, the printed support geometry shifted selectivity toward the target squalane by optimizing the balance between interfacial area and contact time [103].

Lower hydrodynamic resistance. A major practical advantage is the reduction in pressure drop (ΔP) across the catalytic reactor. ΔP directly defines energy demand (blower/compressor duty) and often constrains scale-up. Printed, periodically ordered lattices can reach void fractions of ∼70–90%, while densely packed particle beds typically exhibit only ∼35–40% voidage [1]. Even at higher geometric surface area, a printed body can thus remain more “open.” For instance, BASF’s X3D catalyst exhibits a bulk packing density of 420 kg m⁻³ versus 450 kg m⁻³ for a star-shaped predecessor [4]. In combination with streamlined channels, this produces a substantial gain: in a commercial reactor, X3D delivered a 75% reduction in bed resistance compared with the previous catalyst charge [4]. Quantitatively, the ΔP across the third catalytic layer decreased from ∼16 mbar to ∼4 mbar [4]. This immediately lowered electricity use for air compression by approximately 5–6% (estimate consistent with a 12 mbar drop at a flow of ∼400 kg h⁻¹ SO₂) [4] and reduced caustic consumption in the tail gas scrubber by ∼20% due to a cleaner outlet gas [4]. In a separate example, a printed POCS lattice for Fischer–Tropsch achieved roughly half the ΔP of an equally converting packed bed, underscoring that the “high conversion + low ΔP” combination is difficult to realize with traditional shapes [1].

Improved heat management and temperature control. In exothermic reactions (e.g., oxidation, methanol synthesis, Fischer–Tropsch), hot spots arise from localized heat release and limited heat removal. Printed metallic bodies (and ceramics with thermally conductive additives) increase the effective thermal conductivity of the bed. For an additively manufactured aluminum porous monolith used in Fischer–Tropsch, the axial temperature gradient was reduced from 10 s of °C (packed particles) to <5 °C—nearly isothermal operation, which helped avoid runaway and improved selectivity by suppressing over-production of heavy hydrocarbons. Co-printing a thermally conductive wall with the internal structure further reduces thermal resistance because the lattice is monolithically bonded to the wall, unlike point contacts in packed beds [1]. For endothermic duties (e.g., methane reforming, cracking), the same argument applies in reverse: more uniform heat supply through thermally conductive printed matrices.

Flexibility and accelerated R&D. Additive manufacturing enables rapid prototyping cycles. Shapes that previously required dies or extrusion tooling over months can now be designed and printed within days. Shell emphasizes that rapid printing of catalyst prototypes accelerates discovery and allows for screening of more geometries in short time frames [3]. Very small batches (down to a few monoliths) are feasible for early testing, conserving expensive active components.

Process-tailored, site-specific design. Printed catalysts can be customized to specific reactors or operating windows, including nonstandard hardware. Designs can reflect the real velocity profile in large vessels—e.g., a more open structure near the wall—something not practical with a single extrudate type. BASF frames X3D as a customization platform: the geometry can be adapted in collaboration with the end user for plant-specific conditions [108].

Mitigated deactivation and extended service life. Several deactivation mechanisms are alleviated or moderated:

• Reduced fouling by fines and reaction solids. Regular, larger channels are less prone to clogging by dust or attrition products; monolithic bodies themselves generate less dust because there is no interparticle friction. Field reports indicate no ΔP growth after three years of service with printed blocks, consistent with limited accumulation of fines [4];
• More uniform reactant distribution and temperature. Even flow and temperature fields reduce local starvation/oversupply and hot spots, curbing coking and thermal sintering (e.g., in Fischer–Tropsch, more uniform temperature suppressed carbon deposition and prolonged catalyst life);
• Lower thermomechanical stress. Monolithic bodies avoid grinding and point load breakage typical of granular beds during thermal cycling; materials can be matched to reactor expansion behavior.

Function integration and process intensification. Printing allows multiple functions to be combined in a single object. Examples include catalytic filters (simultaneous particulate capture and oxidation) or catalyst + sorbent architectures. A prominent case is the integrated sorption-enhanced route to dimethyl ether (DME) from CO₂ (CO2Fokus project): 3D-printed bodies hosting both a Cu-based catalyst and a water-adsorbing zeolite shift equilibrium and raise overall yield [109,110]. Such deterministic spatial placement of functions is difficult to achieve by powder mixing and pressing.

Economic considerations. While the unit manufacturing cost of 3D-printed catalysts can exceed that of mass-produced tablets/extrudates, operation-level savings can be material:

• Lower energy use (reduced ΔP);
• Higher productivity or yield at scale;
• Longer service intervals (fewer change outs and less downtime);
• Potential CAPEX relief via smaller reactors if performance gains support reduced volume.

BASF reports a 5–8% throughput increase after transitioning to Quattro and larger gains with X3D—effectively debottlenecking existing assets [4]. Johnson Matthey’s assessment indicated a double-digit improvement in net present value (NPV) for its printed catalyst under an implementation scenario (e.g., +62% NPV) [111]. Actual economics remain case-specific.

Sustainability and environmental impact. Digital, local-to-use manufacturing can shorten supply chains. Energy savings (e.g., ∼5% lower blower power) reduce the carbon footprint; deeper conversion concurrently cuts emissions (e.g., SO₂ reduced from ∼100 ppm to <50 ppm at the outlet) [4]. In biocatalysis and related areas, geometrically complex bodies can be printed from renewable or biodegradable feedstocks, aligning with green chemistry principles.

These advantages should be weighed against current challenges:

• Manufacturing cost and throughput. High equipment cost and limited printing speed impede commodity-scale production. BASF is investing in X3D capacity with a target of serial production by 2026 [112,113], but most deployments remain small-lot or pilot-scale;
• Material constraints. Not all catalytic formulations are readily printable; some require aggressive consolidation (ultrahigh temperatures), have problematic rheology, or involve toxicity concerns;
• Adoption and standards. Plants, test protocols, and handling equipment are optimized for tablets/extrudates. Transitioning to 3D forms necessitates retraining and adaptation of in-house standards;
• Quality assurance. Complex shapes can harbor hidden defects (incomplete consolidation, blocked channels). QA/QC must incorporate nondestructive inspection (e.g., CT) at the lot level.

In sum, the advantages of 3D-printed catalysts—especially in domains where conventional forms approach performance ceilings or where integrated functions are decisive—justify sustained development. As a Shell representative aptly noted, additive manufacturing opens the door to catalyst geometries previously not even considered, enabling reactions once deemed “too difficult” to become attainable [3].

11. Industrial Applications, Case Studies, and Development Trends

At the turn of the 2020s, 3D printing of catalytic structures progressed from laboratory demonstrations to the first industrial trials. Below, we summarize the most significant applications and company case studies, as well as emerging technological trends. Existing companies and technologies are shown in Figure 5.

Figure 5. Technologies of additive manufacturing: classification and leading technology brands [7].

Chemical Industry: Sulfuric acid and environmental processes. A flagship example is BASF’s X3D™ program—a new 3D-printing-enabled catalyst-shaping technology. The first deployments focused on vanadia catalysts for SO₂ oxidation in sulfuric acid production. In 2019, BASF installed a batch of 3D-printed O4 115 X3D™ catalyst at one of its sulfonation plants, noted as the first commercial application of a 3D-printed catalyst [4]. The outcomes were discussed above: a substantial reduction in pressure drop (ΔP) and energy demand was observed, with increased throughput. In 2022, BASF officially announced market rollout of X3D and construction of a new line with startup in 2026 [112,114]. The company indicates that the concept is applicable to a broad range of reactions beyond SO₂ oxidation [4]. Processes frequently cited as near-term candidates include selective catalytic reduction (SCR) of NOx and Regenerative Thermal Oxidizers (RTOs), where ΔP and temperature are critical; BASF also reports projects on 3D-printed adsorbents using the same form optimization logic [108].

Oil and Gas. Companies in the oil and gas sector are exploring 3D-printed catalysts for process intensification in conventional units:

• ExxonMobil and Shell are investing in new shapes for HDT, reforming, and gas-to-liquid (GTL) processes. Shell publicly described prototypes printed for GTL and being tested at its research center [3]. The objective is to target stages that limit overall yield. Shell notes promising results: according to the company, 3D-printed catalysts “give chemical reactions previously considered too difficult a chance to be realized” [3]. In 2025, Shell stated an intent to accelerate rapid prototyping in its research and development (R&D) programs to speed catalyst discovery for CO₂ capture/utilization and waste-to-fuel pathways;
• Rosneft (via its research institute) filed a series of patents in 2019–2020 on 3D printing of catalytic materials (RU 2734425 C2, etc.) [2]. Their focus is optimized pellets for fixed-bed tubular reactors (e.g., reforming and other refining processes). Within the Rosneft 2022 program, additive manufacturing was referenced for new HC and heavy-oil-upgrading catalysts [115]. While public plant-scale data are not yet available, the patenting activity by a major refiner signals strategic interest.

Automotive Catalysts and Exhaust Aftertreatment. Automotive applications represent a vast market where every reduction in ΔP translates to improved fuel economy. Research groups (e.g., EMPA, Switzerland; Papetti et al.) working with industry have printed metallic open-cell structures for catalytic converters [116]. Reported outcomes include faster light-off (via thinner walls), better conversion under transient operation, and 10–15% lower pressure drop relative to equal-volume ceramic honeycombs [116]. While replacing ceramic monoliths in mass production will require scale and cost reductions, specialized vehicles and motorsport are plausible early niches. BASF likewise points to potential X3D applications in heavy-duty vehicles, where ΔP strongly impacts fuel economy [113,114]. In parallel, additive methods have been demonstrated in exhaust hardware—for example, lightweight aluminum supports with catalytic layers to reduce system weight—albeit as one-off examples to date.

CO₂ Conversion and “Green” Chemistry. Catalyst printing aligns well with challenging multiphase CO₂ conversion processes that require nonstandard architectures:

• ZEOCAT 3D (EU Horizon 2020): Direct conversion of CO₂ and methanol to dimethyl ether (DME) over a bifunctional catalyst. VITO (Mol, Belgium) developed 3D-printed supports loaded with zeolite and copper functions and scaled them to a pilot level (technology readiness level, TRL 6) [110]. Monoliths of Ø36 × 10 mm exhibited a higher productivity-to-ΔP ratio than standard tablets; pilot testing at 1 kg·h⁻¹ is being prepared;
• CO2Fokus: Integrated sorption–catalysis structures for single-unit DME synthesis. Laboratory data indicate ~15% higher CO₂ conversion in the 3D-printed reactor than in a traditional one, attributed to optimized placement of water sorption zones [44];
• Electro/photocatalytic devices: Printed porous electrodes for CO₂ electrolysis and photocatalytic cells with catalytic channel walls—here, printing primarily enables complex transport paths for light/current and robust catalyst fixation in microreactors.

Fuel Cells and Energy. Three-dimensional printing is being evaluated for steam-reforming reactor inserts co-printed with the catalyst and for conductive, porous carbon lattices as electrocatalyst supports for hydrogen and fuel cell technologies. These efforts are at the research stage but are expanding.

Biotechnology and Pharmaceuticals. Additive methods have seen a swift uptake in biocatalysis:

• Pharmaceutical microreactors: Continuous-flow units with immobilized enzymes printed directly into chips. A 2023 review (RSC Sustainability) notes 12 enzymatic reactions implemented in flow using 3D-printed reactors with high yields and enantioselectivities [20];
• Bio industry: startups explore printing immobilized cells (yeast, microalgae) in 3D matrices to improve substrate/product transport. “Enzyme cascades” are also being realized by printing sequential microcompartments with distinct enzymes—simplifying purification and enabling plug-and-play reconfiguration compared with co-mixing all enzymes.

Trends. Several technological and strategic trends are shaping the future of 3D-printed catalysts:

• Binderless and “clean” materials. Since organic binders may dilute activity, current work targets printing with little-to-no binder—for example, direct laser sintering of oxides at reduced temperatures via tailored additives. Proof-of-concept binderless ceramics for catalysis have been reported [117];
• Multi-material printing. Equipment capable of depositing 2–3 materials per build—highly attractive for catalysis—already exists (e.g., dual extrusion). This enables gradients and sharply defined functional interfaces (e.g., an inner channel of a magnetic, induction-heatable alloy wrapped by a catalytic shell);
• Digital design libraries and standardization. Catalogs of geometry “archetypes” tailored to common processes may emerge, along with ASTM-style descriptors (e.g., standardized flow/penetration factors) to compare printed and conventional catalysts;
• Cost reduction and scale. With major players entering (e.g., BASF), faster printers (continuous belts, multi-head systems) are being developed to reduce unit cost;
• Artificial intelligence (AI)-assisted material and geometry design. Generative and surrogate models are being used to propose non-intuitive architectures and to optimize printable ink/green body formulations;
• Training and process rethinking. As engineers internalize additive possibilities, new “green” processes (waste valorization, hydrogen economy, power to X, PtX) are being conceived from the outset with nontraditional, structured catalyst options in mind.

In summary, 3D-printed catalytic structures have demonstrated viability and performance benefits in a number of applications, even if they are not yet a mass product. We are witnessing a transition from isolated demonstrations to the first industrial series and units that employ such catalysts. If prevailing trends (lower printing costs, demand for process intensification, customization) continue, broader adoption in the next 5–10 years is plausible as follows:

• In compact, modular plants where conventional forms do not meet size/shape constraints;
• In innovative processes (PtX, CO₂ utilization, biorefining) that need a step change in efficiency;
• In retrofits of existing assets to improve energy efficiency and environmental compliance (as already demonstrated in sulfuric acid).

As with any new technology, success requires removing residual barriers and building user trust. However, the competitive advantages summarized in this review are substantial. It is reasonable to forecast that additive manufacturing will take a firm place in the catalyst engineer’s toolkit, enabling more efficient, sustainable, and economical chemical processes. Existing processes are illustrated in Figure 5.

12. Innovations, Challenges, and Economics

Additively manufactured catalytic structures occupy a unique position at the intersection of engineering, materials science, and chemical technology. Their promise is widely recognized: geometric freedom, functional integration (mixing, heat management, catalytic activity in a single body), and compatibility with process intensification strategies all point to a step change in reactor design and catalytic performance [1]. At the same time, industrial adoption remains limited. The following subsections synthesize the main technical, economic, and organizational barriers; highlight the most dynamic innovation vectors; and outline the prospects for scale-up into high-value processes relevant to energy, environmental management, and biomanufacturing.

12.1. Current Barriers to Industrial Adoption and Economic Constraints

A persistent barrier to widespread industrialization is the cost structure of advanced additive manufacturing infrastructure. High-end SLM systems for metals are priced on the order of millions of RUB, while industrial SLA platforms can reach tens of millions of RUB [118]. For small- and mid-sized laboratories, these capital expenditures (CAPEX) are prohibitive. Unlike extruded monoliths or packed beds—technologies that can often be produced with comparatively inexpensive legacy tooling—metal additive manufacturing demands not only the printer but also controlled atmospheres, powder handling infrastructure, and qualified personnel. As a result, access to state-of-the-art metal printing capacity becomes a strategic bottleneck rather than a commodity service.

Materials stability under realistic catalytic and reactive environments presents another constraint. Polymers generally lose mechanical integrity at 200–250 °C; photopolymers exhibit binder burnout and embrittlement under prolonged heating; ceramics frequently require extended post-processing (e.g., high-temperature sintering) to achieve sufficient density and mechanical strength; and additively manufactured metals may suffer corrosion, especially in sulfur- or chlorine-containing feeds. Ryu et al. demonstrated that even modest increases in binder content in SLA-derived alumina (Al₂O₃) sharply reduce photostability, underscoring the narrow processing window between printability and long-term durability [119]. This sensitivity complicates qualification for harsh industrial environments such as HDT, partial oxidation, and reforming.

Scale remains a third barrier. Many of the most successful demonstrations of 3D-printed catalytic reactors operate at laboratory or pilot throughput. For example, gyroidal Ni-based lattices have delivered excellent performance in CO₂ methanation [120]. However, translation of such geometries to full industrial reactors is limited by build volume, print duration, and precursor cost. Large, monolithic TPMS bodies with integrated heat exchange are still difficult to fabricate in sufficient numbers to support multi-ton/day product streams.

These manufacturing and scale constraints couple directly to the economics of adoption. On first inspection, the high CAPEX of specialized printers appears to weaken the business case relative to mature, extruded catalysts and conventional reactor hardware. However, a more complete techno-economic view must include operating expenditures (OPEX) over the lifetime of the reactor. Several features of 3D-printed catalytic architectures can reduce OPEX in continuous processes such as CO₂ methanation, biogas upgrading, and volatile organic compounds (VOCs) abatement [1,121]:

• Task-specific tailoring of geometry. Lattice and TPMS structures can be optimized for targeted flow regimes and reaction kinetics, improving mass and heat transfer and raising per-volume productivity [121]. Higher per-reactor efficiency means fewer parallel trains for the same throughput, reducing the total number of units that must be installed, monitored, and maintained [1].
• Thermal management and asset lifetime. Improved uniformity of temperature profiles suppresses local overheating and associated sintering or poisoning of the active phase, extending catalyst service life and reducing changeout frequency [121]. Longer service life translates into fewer shutdowns, less labor-intensive replacement activity, and lower consumption of high-value catalytic metals across a multi-year operating horizon.
• Functional integration. Additively manufactured bodies can combine mixing, heat exchange, and catalysis within a single element [1]. This consolidation can shrink plant footprint and simplify piping and auxiliary equipment, which in turn lowers maintenance burden and energy consumption during operation.

In other words, although CAPEX for advanced additive platforms is currently high, their downstream effect on OPEX can partially offset or even invert the initial disadvantage when evaluated over continuous, long-horizon operation. This dynamic is especially relevant for modular, containerized, or distributed plants—settings in which staffing levels, scheduled maintenance windows, and energy efficiency dominate lifecycle costs rather than raw equipment purchase price.

Finally, post-processing remains a non-trivial cost and timeline amplifier. Most printed catalyst supports still require calcination, metal infiltration, impregnation of the active phase, or thermal debinding/sintering steps after printing. Dizon et al. showed that for polymer-derived parts, the aggregate cost of post-processing can approach that of the printing step itself [101]. Each added thermal or chemical treatment stage increases lead time and introduces variability, which complicates both quality assurance and cost forecasting at scale. From an industrial perspective, this erodes some of the theoretical “print → install” simplicity often advertised for additive manufacturing.

Taken together, these constraints (capital intensity, materials stability, build volume limits, and multi-step finishing) delineate why so many systems demonstrated in the literature remain at laboratory or pilot-ready technology maturity rather than at routine commercial deployment [1,118,119,120,121,122].

12.2. Innovation Landscape: Toward Intelligent, Integrated, and Rapidly Optimized Reactors

Despite the above challenges, the innovation pipeline in additive catalytic technologies has accelerated substantially. Several trends are reshaping what an “industrial catalyst” might look like in the coming decade.

Multifunctional and instrumented structures. One of the most active directions is the design of “smart reactors,” i.e., printed catalyst bodies that embed sensing functions (temperature, pressure drop, composition, pH) directly into the lattice [1]. Such integration enables true operando monitoring rather than post hoc analysis. In principle, this supports dynamic process control, early fouling detection, and adaptive heat management, all of which further reinforce the OPEX advantages discussed above [1,121].

AI-assisted geometric design. Modern machine learning workflows are being adapted to automatically generate and optimize CAD geometries for catalytic reactors. Neural-network-driven tools can explore TPMS and related metamaterial families and propose candidate structures that meet specified transfer coefficients, pressure drop targets, or residence time distributions [123]. By learning structure–performance relationships, these algorithms can shorten design cycles by orders of magnitude relative to manual CAD iteration, thereby reducing both engineering labor and trial-and-error printing time.

Lab-on-a-chip (LoC)/reactor-on-a-chip workflows. Additive manufacturing is being combined with microfluidics and robotic handling to build miniaturized screening platforms in which dozens of catalyst formulations can be evaluated in parallel under flow [104]. This approach collapses synthesis, testing, and data acquisition into a single automated loop. The consequence is faster discovery of active formulations and reactor motifs without committing to expensive, full-scale prints at an early stage.

Hybrid and functional inks. A further frontier is direct printing of catalytically active formulations. Researchers are developing printable “inks” and pastes containing MOFs, enzymes, or nanoparticles, allowing the catalytic phase to be incorporated during printing rather than immobilized in a subsequent impregnation step [124]. This strategy could reduce both the cost of and variability in post-processing, directly addressing one of the bottlenecks identified in Section 12.1.

Collectively, these innovations indicate that 3D-printed catalysts are not merely substitutes for extruded pellets, monoliths, or packed beds. Instead, they are evolving toward multifunctional reactor modules that integrate catalytic activity, transport management, sensing, and (in some cases) self-diagnostics [1,123,124,125]. This reframes the business case: rather than comparing a printed lattice to a single-function conventional catalyst body on a per-kilogram cost basis, one must compare an integrated printed module to an entire process unit (reactor + static mixer + heat exchanger + monitoring hardware). That comparison substantially improves the apparent cost–benefit ratio in steady-state operation [1,121].

12.3. Standardization, Digitalization, and Knowledge Transfer

Technical maturity alone will not guarantee industrial uptake. Organizational, regulatory, and knowledge-transfer structures remain underdeveloped.

Standardization. The current literature is characterized by bespoke geometries, unique calcination or impregnation protocols, and disparate test conditions, which makes direct comparison between studies difficult and slows regulatory acceptance. ISO/ASTM 52900 and related additive manufacturing standards explicitly stress the need for domain-specific qualification procedures for chemical and catalytic applications [126]. The development of certification frameworks analogous to Good Manufacturing Practice/Good Laboratory Practice (GMP/GLP) is viewed as essential, particularly for pharmaceutical synthesis and fine chemicals [127]. Without harmonized definitions of acceptable porosity, mechanical strength, leaching behavior, and catalytic stability, printed catalysts will continue to face barriers to approval in regulated environments.

Open CAD/STL libraries and digital twins. A natural next step is the establishment of open repositories of validated lattice and TPMS geometries, ideally with annotated process envelopes (temperature, pressure, flow regime). If an engineer in Berlin and a researcher in Novosibirsk can start from the same stereolithography (STL) model and adapt it to different chemistries or scales, technology transfer accelerates dramatically. First initiatives of this kind—public or semi-public libraries of metamaterial lattices—are already appearing on community platforms [128]. Coupling such libraries with CFD and automated optimization pipelines would allow for semi-autonomous selection (or even generation) of reactor geometries based on specified performance targets (e.g., pressure drop, heat removal rate).

Human capital and interdisciplinary curricula. Skill requirements for the “catalyst engineer” are rapidly expanding. Modern practitioners must combine surface chemistry and catalytic kinetics with CAD literacy, CFD modeling, and additive manufacturing process control. Interdisciplinary educational programs integrating these domains are already emerging in Germany, China, and the United States; comparable initiatives are only beginning to form in Russia. The ability to train personnel who are fluent across chemistry, digital design, and AM hardware is now as critical as access to the printers themselves. In practice, the shortage of such cross-trained specialists can be as limiting as the lack of formal standards.

12.4. Strategic Application Domains and Sustainability Drivers

The most dynamic near-term application areas—biocatalysis/biomedicine and low-carbon energy/chemistry—illustrate how technological potential, regulatory context, and macroeconomic pressures intersect.

Biocatalytic and medical systems. Additive manufacturing of biocompatible lattices based on hydrogels, alginates, and polymer matrices with immobilized enzymes enables compact, modular bioreactors suitable for pharmaceutical synthesis and continuous-flow biocatalysis [20,129]. Donate et al. reported that 3D-printed PLA-based composite scaffolds can preserve enzymatic activity for up to 10 days without significant degradation, pointing toward robust, reusable biocatalytic modules [130]. Such constructs also align with trends in tissue engineering and therapeutic manufacturing, where sterile, single-use or few-use reactor cartridges are attractive from both regulatory and contamination control standpoints [20,129,130]. Here, again, the economics are lifecycle-driven: lower downtime for cleaning/validation and rapid changeover between products can outweigh elevated CAPEX for the initial printed reactor hardware, particularly in high-margin pharmaceutical settings.

Energy efficiency, CO₂ utilization, and the climate agenda. The chemical industry is under intensifying pressure to reduce carbon intensity and improve energy efficiency. Additively manufactured catalytic structures play directly into this agenda via several pathways:

• Ni- and NiCu-based TPMS lattices produced by SLM have shown promising activity for CO₂ methanation, a route to valorize CO₂-rich streams and biogas into synthetic natural gas [120].
• TiO₂ gyroid structures deliver enhanced photocatalytic degradation of organic contaminants, improving water treatment efficiency under light-driven conditions [131].
• Metal–ceramic printed lattices are being explored for integration into fuel cells and water electrolysis, aiming at improved mass transport and tailored current distribution for hydrogen production and utilization [132].

These examples indicate that 3D-printed catalysts are increasingly embedded in processes central to decarbonization and circular carbon use [120,131,132]. Importantly, many of these are continuous processes, which favor the OPEX advantages outlined earlier: uniform thermal management, longer catalyst lifetime, reduced maintenance interventions, and compact intensified reactor footprints [1,121]. In other words, the same characteristics that improve sustainability metrics (higher conversion per reactor volume, better heat and mass transfer, reduced waste) also drive economic competitiveness at the plant scale.

12.5. Outlook: From Demonstration to Deployment

In just over a decade, additive manufacturing for catalytic applications has progressed from proof-of-concept laboratory elements to functional pilot-scale reactors capable of handling realistic feed streams. The field is now poised between two modes of development.

On one side, there is technical maturation: increasingly sophisticated multifunctional lattices; AI-driven, rapidly optimized TPMS and gyroid structures; hybrid inks that co-print support and active phases; and microfluidic discovery platforms that compress catalyst screening timelines [1,120,123,124,125]. On the other, there is system-level integration: standardization under ISO/ASTM-style frameworks, qualification pathways inspired by GMP/GLP for regulated chemistries, shared CAD/STL libraries linked to CFD, and coordinated training of personnel who can bridge catalysis, reactor engineering, and additive manufacturing [106,107,108].

Economic considerations connect these two sides. High CAPEX remains a deterrent [118], yet when one evaluates the full reactor module—not just the catalyst body in isolation—3D-printed systems can deliver lower OPEX over long-term, continuous duty. Enhanced thermal management, process intensification through functional integration, improved asset lifetime, and modular deployment all translate into fewer units to install, monitor, and service [1,121,122]. In sustainability-driven applications such as CO₂ utilization, wastewater remediation, and green hydrogen production, these advantages are strategically aligned with regulatory and societal pressure for decarbonization [20,120,129,130,131,132].

Consequently, the near-term prospects of 3D-printed catalytic structures are defined not solely by advances in printing resolution or material compatibility but by the degree to which the community can (i) codify best practices and qualification metrics, (ii) share and reuse digital reactor geometries, and (iii) educate a workforce fluent in both catalysis and additive manufacturing. Addressing these “soft” challenges is now as important as solving the remaining “hard” problems in materials stability and large-scale fabrication. The concluding section of this work synthesizes these requirements and positions additively manufactured catalytic reactors as key enablers of sustainable chemistry and modular, digitally designed production.

13. Conclusions

Three dimensionally (3D)-printed catalytic structures constitute a qualitative step change in the design and operation of reactors. Whereas conventional pellets and monoliths primarily played a passive role as supports, contemporary architectures—TPMS (triply periodic minimal surfaces), lattice, and fractal constructs—turn geometry into an active design lever for governing the process [27,133,134]. This review shows that additive manufacturing enables marked gains in mass/heat transfer efficiency, lower pressure drop (ΔP), and more uniform distribution of active phases. These advantages position 3D printing not as a mere auxiliary technique but as a foundational tool for developing next-generation catalysts.

A classification by constructive type, material, geometry, and fabrication method underscores the breadth of available solutions. Printing routes compliant with ISO/ASTM standards—FDM (fused deposition modeling), SLA (stereolithography), DIW (direct ink writing), SLM (selective laser melting), and EBM (electron beam melting)—provide design flexibility, while subsequent post-processing and functionalization convert a printed preform into a fully functional catalyst. The literature and industrial case studies (BASF X3D, the CO₂Fokus and ZEOCAT 3D projects, and patents from Shell and Rosneft) indicate that 3D-printed systems are progressing from laboratory prototypes toward industrial deployment, especially in CO₂ conversion, photocatalysis, and biotechnologies [2,135,136,137,138].

At the same time, several constraints persist: high equipment cost, a limited palette of durable materials, and scale-up challenges. Economic analyses suggest that, despite substantial capital expenditures (CAPEX), operating expenditures (OPEX) can be reduced through ΔP minimization and extended service life of the structures. Innovation frontiers—multifunctional objects (catalyst + sensors), AI-assisted geometric design, and integration with robotic screening (lab-on-a-reactor)—are opening new horizons [126,139,140]. However, broader adoption will require further standardization of materials, geometries, and test protocols, along with the development of open CAD/STL libraries tailored to catalytic applications.

In sum, 3D-printed catalysts should be regarded as an inherently interdisciplinary platform uniting materials science, chemistry, engineering modeling, and digital manufacturing. Their significance is particularly pronounced for sustainable and “green” chemistry: modular reactors for low-throughput production, CO₂ utilization units, photocatalytic systems, and bioreactors. The evidence surveyed here suggests that, over the next 5–10 years, such structures may form the backbone of a new generation of chemical process technologies in which design flexibility and reproducibility are combined with high efficiency and environmental compatibility.