Applications and Perspectives of Life Cycle Assessment in the Green Design of Single-Atom Catalysts

Abstract

Single-atom catalysts (SACs) have attracted extensive attention owing to their outstanding catalytic performance and nearly complete atom utilization efficiency. However, the environmental sustainability of SACs across their full life cycle has not yet been systematically investigated. This review emphasizes the necessity of integrating life cycle assessment (LCA) into SACs to support their sustainable development. By analyzing the structural characteristics, synthesis strategies, and representative application fields, this study examines how LCA principles can be employed to reveal the hidden environmental burdens associated with raw material extraction, synthesis processes, usage stages, and end-of-life management. Based on existing LCA case studies of catalytic materials, this review identifies the key challenges in the SACs field and proposes a preliminary framework for sustainable SAC design with LCA as a guiding approach. Finally, the review summarizes the current challenges and future perspectives, emphasizing that developing more specific evaluation standards, improving database construction, and adopting dynamic assessment methods are essential to shift LCA from a passive evaluation tool to an active design strategy that drives the green development of next-generation SACs.

1. Introduction

In recent years, single-atom catalysts (SACs) have shown great promise across diverse catalytic applications due to their unique structural features and high catalytic efficiency. For example, Fe(OH)_x/P-C catalysts exhibit excellent activity for the oxygen evolution reaction (OER) in energy conversion systems [1], Pd-based SACs outperforming homogeneous systems in Suzuki coupling [2], and various SACs efficiently removing NO_x and volatile organic compounds (VOCs) in environmental remediation [3,4]. Unlike conventional nanocatalysts, SACs feature isolated metal atoms that are stabilized on supports through coordination bonding. This atomically dispersed configuration not only maximizes atom utilization and ensures uniform activities sites but also provides new possibilities for electronic structure regulation [5]. As a result, SACs achieve activity comparable to homogeneous catalysts while maintaining the easy separation and durability characteristic of heterogeneous systems [6]. In this sense, they effectively bridge the gap between homogeneous and heterogeneous catalysis.

Current research on SACs mainly focuses on tuning coordination environments, improving stability, exploring non-metallic SACs, and clarifying reaction mechanisms. However, the environmental impacts and resource consumption associated with their synthesis and use have received far less attention. The preparation of SACs is often associated with the use of costly metal precursors, elaborate surface engineering steps, and high-temperature thermal treatments [7]. Such processes consume large amounts of energy and may generate toxic by-products, raising sustainability concerns. In addition, their stability may be undermined by atom migration or collapse of coordination environments [8], which in turn leads to increase energy demand and raw-material consumption, amplifying environmental risks. With the growing global focus on green chemistry and sustainable development, the pathway of SACs toward environmentally benign and resource-efficient solutions becomes particularly urgent. Life cycle assessment (LCA), as a systematic method for quantitatively analyzing environmental impacts [9], provides a powerful framework to identify the environmental costs hidden in every stage, from raw material extraction and catalyst synthesis to operation and final disposal [10,11,12]. LCA therefore serves as an indispensable reference for green design and sustainability-oriented strategies.

At present, however, the integration of LCA into SAC research is still at a preliminary stage. Existing studies tend to evaluate overall catalytic processes rather than the sustainability of SACs themselves. Nevertheless, a few recent studies have begun to quantify their sustainability performance. For instance, Bajada et al. [13] evaluated the life-cycle impacts of SACs in heterogeneous catalysis and reported notable reductions in ecosystem and human health damage compared with conventional nano catalysts. Similarly, Weber et al. [14] analyzed atomic layer deposition (ALD) processes from an environmental perspective, illustrating how synthesis parameters directly affect energy consumption and emissions. These studies mark early efforts to define sustainability metrics, such as global warming potential (GWP) and resource depletion, for SAC systems, yet comprehensive frameworks linking synthesis strategies with environmental indicators remain limited. Integrating LCA into SAC synthesis allows quantification of the environmental cost associated with precursor selection, temperature regimes, and solvent usage, thereby revealing the trade-offs between catalytic efficiency and environmental performance. This coupling of synthesis and LCA establishes a critical intersection that guides the rational design of greener SACs [15].

In this context, this review systematically examines the potential benefits and practical approaches for applying LCA in SAC research. The following sections introduce the structural features, synthesis methods, and application status of SACs, then outline the theoretical foundation and evaluation procedures of LCA, followed by an exploration of its feasibility in SAC research. Finally, by drawing on representative case studies in catalyst and energy-material LCA, we propose a preliminary sustainability evaluation framework for SACs that can serve as a theoretical and methodological reference for future green catalyst assessments.

2. SACs and Their Environmental Implications

2.1. Performance Advantages

Since the pioneering report of Pt/FeO_x catalysts for CO oxidation by Zhang and co-workers in 2011 [16], SACs have rapidly become a research hotspot due to their isolated atomic sites and nearly complete atom utilization efficiency [17]. Recent advances in aberration-corrected scanning transmission electron microscopy (AC-STEM), X-ray absorption spectroscopy (XAS), and other advanced characterization techniques have made it possible for researchers to directly probe atomic configurations and electronic states [6,18]. Together, these tools have established a strong foundation for linking local coordination and electronic structures to overall catalytic performance, forming the basis of reliable structure–activity relationships.

As illustrated in Figure 1, the catalytic performance of SACs arises from their unique atomic-level coordination environments. Typical active centers include transition metals such as Fe, Co, Ni, Pt, and Pd, which form stable M-N_x or M-O_x structures through coordination with heteroatoms (N, O, S) on the supports [19]. These coordination environments modulate electronic structures, regulate adsorption behaviors, and lower energy barriers [20], thereby enhancing both activity and selectivity. Consequently, the choice of support is crucial for tuning SAC performance, either by local structural regulation or by coupling effects between the support and the active site. Carbon-based supports, with abundant surface defects and excellent conductivity, provide outstanding anchoring sites for electrocatalytic SACs [21]. Metal–organic frameworks (MOFs) and their derivatives, possessing ordered porous structures and abundant coordination sites, have also been extensively employed for high-loading SACs [22]. Similarly, oxide supports such as TiO₂ and CeO₂. which contain oxygen vacancies and strong metal–support interactions (SMSI), are particularly suitable for redox systems [23].

Although such structural strategies markedly enhance activity and selectivity, their environmental implications are often overlooked. For instance, the synthesis of MOF precursors frequently involves multi-step use of toxic organic solvents and high-temperature carbonization [24]. Under harsh reaction environments, some coordination structures may collapse, causing metal aggregation or carrier decomposition and introducing additional environmental risks. These considerations highlight the urgent need to integrate green design principles into SAC development.

2.2. Synthetic Strategies

Main methods for SAC synthesis include high-temperature pyrolysis, wet-chemical techniques, and atomic layer deposition (ALD) [25]. Pyrolysis, widely used to construct M–N–C structures, is typically carried out under inert gas atmospheres at temperatures exceeding 800 °C [26]. Although effective, this process is energy-intensive and can generate CO₂ along with complex volatile organics, implying notable environmental burdens. Wet-chemical methods, including co-precipitation, impregnation, and ion exchange introduce metal precursors onto supports under relatively mild and controllable conditions [27]. However, they are generally unsuitable for high metal loadings and rely on hazardous chemicals. Resulting waste streams may contain unreacted metal ions, salts, organic ligands, or solvent residues [28], posing notable risks. ALD, in contrast, achieves atomically precise deposition by alternately pulsing gaseous metal precursors and reactants [29]. This method eliminates the need for bulk solvents and offers excellent controllability, yet it relies on highly toxic precursors such as MeCpPtMe₃ or TMHD [30], and requires careful treatment of gaseous byproducts.

In recent years, greener alternatives such as mechanochemical milling and electrochemical deposition have emerged [31]. These methods generally operate under milder conditions with lower solvent use, thus reducing environmental burdens [32,33]. However, issues of uniformity, support compatibility, and scalability still constrain their broader application.

The environmental profiles of these synthesis routes vary substantially, not only in terms of pollutant types and toxicity, but also in energy demands, resource efficiency, and waste management throughout the life cycle [34]. Therefore, the environmental impacts of SAC synthesis are highly pathway-dependent. Evaluating only metrics such as yield or metal loading without considering life-cycle burdens risks underestimating hidden environmental costs [14].

2.3. Practical Applications

With the advancement of SAC research, their potential has been demonstrated in electrocatalysis, organic synthesis, and environmental catalysis. However, translating these advances into practical applications remains challenging. In electrocatalytic reactions such as the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and CO₂ reduction (CO₂RR) [35], SACs have become promising candidates owing to their high activity and favorable electron transport. Yet under harsh conditions, including strong acids, strong bases, or high potentials, metal centers may dissolve or redeposit, thereby compromising stability and shortening catalyst lifetimes [36]. In organic transformations, SACs face similarly complex conditions. They often achieve high selectivity, issues related to separation, recycling, and metal leaching remain unsolved [37]. For example, a Pd-ZnO-ZrO₂ SAC developed by Ding et al. achieved 99% yield in Suzuki–Miyaura coupling without phosphine ligands or inert atmospheres and maintained activity over five cycles. However, such durability is still short of industrial requirements, and performance under extreme or impurity-rich conditions awaits further verification [38].

In environmental remediation, SACs have shown potential for degrading VOCs, reducing NO_x, and treating wastewater [39]. Yet in realistic complex matrices, SACs may suffer deactivation [40], while leached metals and degraded supports can release micro/nanoparticles into the environment, potentially creating new ecological risks [37]. Bridging the gap from model systems to field applications therefore requires integrated evaluation protocols that simultaneously assess activity, stability, and leaching behavior under realistic operating conditions.

2.4. Potential Ecological and Health Risks

Although SACs are widely regarded as green catalysts owing to their high efficiency and tunable structures, their environmental and health implications remain poorly understood. Evaluating the sustainability of SACs therefore requires metrics beyond conventional performance indicators, encompassing risks across the entire life cycle rather than focusing solely on yield or pollutant removal efficiency.

Compared with nanoparticles, single-atom centers exhibit higher mobility and stronger interfacial reactivity. This raises concerns about potential structural breakdown, metal release, and byproduct formation during operation and disposal [41]. For instance, dissolved metal atoms can interact with natural organic matter or adsorb onto microplastics, altering their mobility and bioavailability and thereby inducing ecological effects [42,43]. Even trace amounts of noble metal ions can interfere with aquatic metabolism, and long-term accumulation may generate persistent ecological risks [44].

Human health risks also deserve attention. During synthesis and recycling, operators may be exposed to trace metals or nanoscale dusts. While dedicated studies remain limited, occupational health research on nanomaterials suggests that fine particles can cause cumulative damage to the respiratory and immune systems [45]. On an industrial scales, waste solvent effluents and discarded SACs may emerge as new pollutant sources [46], underscoring the need for exposure control, environmental monitoring, and end-of-life management. These considerations highlight that the “greenness” of SACs must ultimately be verified through comprehensive LCA.

3. LCA Methods and Applications in Catalyst Research

3.1. Fundamentals of LCA

LCA is a systematic tool for quantifying the environmental impacts of a product or technology throughout its entire life cycle. According to ISO 14040 [47] and ISO 14044 [48], LCA encompasses all stages from raw material extraction to final disposal, enabling researchers to track resource use and pollutant emissions, identify environmental hotspots, and ultimately guide greener design and environmental management. Originally developed as a policy support tool, LCA has now become a widely adopted scientific methodology in energy, chemical engineering, and materials science, and has increasingly evolved into a key instrument for research evaluation.

Three major methodological approaches are typically distinguished: process-based LCA, input–output LCA, and hybrid LCA [47,48]. Process-based methods can track material and energy flows in detail and are well-suited for laboratory or pilot-scale SAC synthesis studies, but they require extensive data collection and thus have high costs. Input–output methods, in contrast, use economic input–output tables to estimate environmental impacts at a macro scale, making them suitable for sector-level assessments but less sensitive to atom-level processes in emerging materials. Hybrid LCA aims to integrate the accuracy of process-based approaches with the scalability of input–output methods, offering particular promise for evaluating SACs in future applications [49,50]. For SACs, which are still in their early stage of development, ensuring both data reliability and model scalability will be crucial for meaningful assessments. Adopting flexible methodological choices or multi-scale hybrid models can better capture the environmental burdens across the life cycles of SACs. Recent advances in digital technologies offer new opportunities to overcome data limitations in the LCA of SACs. Machine learning algorithms can predict material properties and estimate missing inventory data based on synthesis parameters, while automated data pipelines and high-throughput simulations improve the temporal resolution of LCA modeling. Integrating these digital tools within hybrid LCA frameworks can significantly enhance data reliability and reduce uncertainty in early-stage catalyst evaluation [51].

The standard LCA framework consists of four stages (Figure 2): goal and scope definition, life cycle inventory (LCI), life cycle impact assessment (LCIA), and interpretation. In the goal and scope stage, researchers define the functional unit (FU), for example, “the environmental burden per 1 mol of CO₂ converted,” and set system boundaries, such as whether to include raw material transportation, use-phase impacts, or waste treatment [52]. In the LCI stage, data are collected on all relevant inputs and outputs, such as energy consumption, raw material use, and waste emissions. These inventory data are then transformed in the LCIA stage into quantifiable environmental impact categories, such as global warming potential (GWP), acidification potential (AP), resource depletion, human toxicity, and ecotoxicity [53,54]. Finally, the interpretation stage involves analyzing uncertainties, conducting sensitivity studies, and drawing conclusions that can inform design optimization.

3.2. Feasibility of Applying LCA to SACs

Despite their obvious catalytic advantages, SACs pose significant challenges for the application of LCA. These challenges arise from their complex raw material compositions, diverse synthesis pathways, low yields, and unresolved issues regarding stability and recyclability [55]. Therefore, accurate life-cycle modeling requires detailed tracking of material and energy flows, as well as careful attention to system boundary definitions.

For example, Fàbrega and co-workers [56] constructed a cradle-to-gate LCA model for Pd-based SACs used in Sonogashira reactions. Their study quantified the contributions of high-purity precursor production, high-temperature pyrolysis, and recyclability to the overall environmental burden. It also highlighted how the section of functional units and boundary definitions strongly shape the results. Although published LCA studies specifically targeting SACs are still rare, an increasing number of researchers have begun to extend LCA into advanced materials such as batteries, photovoltaic components, and carbon nanomaterials [57,58]. Quan et al. [59] conducted a cradle-to-grave LCA of lithium iron phosphate (LFP) and nickel cobalt manganese oxide (NCM) batteries, covering production, use, repurposing, and recycling. They found that recycling, especially hydrometallurgy, greatly reduces overall environmental impacts and offers useful insights for catalyst-related systems. Integrating atomically dispersed active sites with robust supports has inspired more sustainable catalyst designs. For example, the study “Designer topological single-atom catalysts with site isolation” showed that rational atomic configuration can enhance both performance and stability, providing useful insights for LCA-based green design [60]. These early applications show that even with incomplete data, LCA offers a credible evaluation framework capable of guiding sustainable design strategies. Moreover, these challenges intensify at the nanoscale and atomic scale, where defining functional units and scaling material flows involve inherent uncertainties. Conventional LCA databases fail to represent phenomena such as atomic dispersion, migration, or leaching, resulting in persistent issues of data scarcity and scale translation in the LCA of single-atom catalysts.

From the perspective of catalytic performance, the high efficiency of SACs can reduce energy consumption and improve resource utilization. Yet from a materials perspective, their main environmental burdens lie in synthesis, application, and end-of-life management. In this respect, LCA offers not only a quantitative assessment of the impacts of SACs but also a theoretical foundation for optimizing synthesis routes and identifying greener alternatives [47,48]. Importantly, integrating LCA results with catalytic performance metrics [60] can help shift research priorities. Rather than optimizing SACs solely for activity or selectivity, researchers are increasingly encouraged to consider the life-cycle sustainability of these systems when designing new catalysts.

3.3. The Necessity of LCA in SAC Research

As noted in previous sections, SACs face potential environmental and resource-related risks across their life cycle, from raw material extraction and catalyst synthesis to actual operation and disposal. Evaluating their sustainability thus requires more than qualitative discussion; it demands systematic and quantitative analytical tools. In this context, LCA is indispensable because it integrates all stages into a coherent framework and captures synergies and trade-offs that isolated analyses would miss [13,61].

At the raw material stage, SACs frequently depend on high-purity precursors, especially precious metals such as Pt, Pd, and Ir. The mining and refining of these metals result in substantial pollutant emissions, and their CO₂ footprints far exceeding those of base metals [62]. For instance, Rinne et al. [63] showed through LCA modeling that producing battery-grade Co sulfate from cobaltite ore generate a global warming potential of 20.9 kg CO₂ eq/kg, with 12.7 kg attributed to hydrometallurgical processing. Even more abundant metals like Ni and Fe also involve energy-intensive refining steps that release CO₂ and generate acidic wastewater.

Likewise, synthesis methods vary sharply in their environmental burdens. Although LCAs directly focusing on SACs are lacking, a study on ZIF-8 (an MOF-based material) compared five synthesis routes and revealed stark differences. The most environmentally benign route used deionized water as a solvent, whereas the least sustainable one relied on DMF, with washing steps requiring DMF/MeOH mixtures. The differences in ecological and human health impacts between the two routes reached as high as 93–95% [34]. These results clearly demonstrate that even for the same support material, optimizing synthesis routes can drastically reduce environmental costs-underlining the necessity of applying LCA to SAC synthesis.

During operation, the atomically dispersed active sites in SACs improve atom efficiency and can theoretically lower catalyst loading and energy demand [64]. On the other hand, real-world operating conditions, such as high temperatures, electric fields, strong acids/bases, SACs often experience structural degradation and metal leaching [65]. In some cases, new devices designs are required to mitigate these losses. For example, Chen et al. [66] developed a fuel-cell-like flow reactor embedding Pt SACs into MoS₂/graphite felt, aiming to reduce metal leaching while preserving catalytic potential. Still, structural collapse and leached metals entering the environment remain serious concerns, with potential long-term toxicity to aquatic ecosystems.

The interconnectedness of the life cycle stages of SACs adds further complexity. Benefits in one stage may come at the expense of burdens in another. For example, a comparative LCA between conventional Pt/C catalysts and Fe-N-C SACs showed that Fe-N-C could reduce ecosystem and human health damages by 88–90% and 30–44%, respectively. However, its synthesis consumed more energy, raising GWP by 53–92% [67]. Similarly, if recycling and reuse are inefficient, end-of-life impacts can offset environmental advantages gained in production [56].

These findings underscore the necessity of LCA, as performance metrics such as conversion efficiency alone cannot capture the complete sustainability picture. As shown in Figure 3, embedding LCA into SAC research enables material development to balance activity improvements with environmental burdens, advancing toward a truly green and sustainable future. The outcomes of LCA can directly inform catalyst selection and process optimization in industrial applications. Identifying energy-intensive synthesis steps or high-impact precursors allows engineers to prioritize greener alternatives or adjust reaction parameters to reduce environmental footprints. When scaling up, integrating LCA with techno-economic analysis (TEA) further supports decisions regarding the commercial viability of single-atom catalyst systems.

4. Exploring an LCA Framework for the Sustainable Design of SACs

4.1. Defining System Boundaries and Functional Units

The first step of LCA is to establish clear system boundaries, which define the scope of the study, specifying which processes, activities, or elements should be included and which can be excluded [68]. The definition of system boundaries directly shapes the completeness and comparability of the LCA results.

System boundaries can be defined at different levels of specificity. As illustrated in Figure 4, the two most commonly used frameworks are the “cradle-to-gate” and “cradle-to-grave” approaches. The cradle-to-gate approach typically focuses on processes occurring before a product leaves the manufacturing facility. It includes raw material extraction, synthesis, and production. This boundary is useful for studies aiming to evaluate the environmental impact of individual products or materials in their manufacturing phase. On the other hand, the cradle-to-grave approach extends the scope to include the use phase, recycling, and end-of-life treatment, thereby providing a comprehensive analysis of the product’s entire life cycle. In catalyst development, particularly for SACs, cradle-to-grave is essential because it also captures the long-term environmental impacts, such as catalyst degradation and recycling [69].

For instance, Chen et al. [60] applied a cradle-to-gate LCA to compare a Mn/CeO₂ single-atom catalyst with a traditional V-W-Ti catalyst at different reaction temperatures, assessing their 100-year global warming potential (GWP₁₀₀). The results showed that while the GWP₁₀₀ of the V-W-Ti system decreased gradually with rising reaction temperature, it remained relatively high overall. In contrast, Mn/CeO₂ consistently exhibited significantly lower GWP₁₀₀ across all temperatures, demonstrating the clear carbon footprint advantage of SACs over conventional catalysts.

However, as SAC research shifts toward large-scale applications, the cradle-to-grave boundaries become more suitable. This expanded scope builds on cradle-to-gate by including catalyst service life, recycling, and end-of-life treatment [56]. Particularly for recyclable SACs, the disposal stage can strongly influence the overall environmental profile. Some studies using cradle-to-grave assessments have found that when catalyst recycling rates exceed 90%, overall resource consumption across the lifecycle can be reduced by nearly 50% [13].

Furthermore, the functional unit (FU) plays a pivotal role in standardizing comparisons among different products or systems within LCA studies. In SAC research, the FU is typically defined according to the specific application, for instance, “per kilogram of hydrogen produced” in electrocatalysis for fuel cells, or “per mole of pollutant removed” in environmental applications [70,71]. Defining the FU ensures that comparisons across studies are meaningful, as it normalizes the performance of catalysts and provides a quantifiable basis for evaluating the impacts of SACs in various catalytic processes. Moreover, defining the FU at the onset helps streamline data collection and ensures that the LCA is tailored to the specific objectives of the study.

4.2. Building the Life Cycle Inventory (LCI)

The goal of the inventory stage is to collect, as comprehensively as possible, all relevant input and output data, including the consumption of raw materials, energy, and water, as well as emissions of gases, liquids, and solids. This stage is essential because it forms the foundation of the entire LCA process and directly informs the subsequent impact assessment phase. For SACs, the inventory data should cover all stages of the catalyst’s life cycle, including synthesis, activation, and recycling, with particular attention paid energy consumption, metal precursors, and emissions during catalyst synthesis.

For background processes such as electricity generation, fossil fuel consumption, or transport [72], researchers can typically draw from existing lifecycle databases. Widely used resources include Ecoinvent, International Reference Life Cycle Data System (ILCD), and Building for Environmental and Economic Sustainability (BEES) [73,74]. These databases provide systematic datasets, such as greenhouse gas emissions per kWh and energy intensity per ton of chemicals, and are compatible with major LCA platforms including SimaPro, OpenLCA, and GaBi [75].

However, for advanced materials like SACs, which possess highly specific structures and intricate synthesis pathways, these general-purpose databases are often insufficient [76]. On the one hand, SACs often rely on trace amounts of precious metals, nanostructured carbon supports, and atmosphere-controlled thermal treatments, all of which are not standardized in current databases. On the other hand, the available data are usually industry-level averages at the macro scale, which fail to adequately represent the environmental impacts of laboratory- or pilot-scale operations. For instance, existing databases often lack emission records for particulates or NO_x generated from high-temperature processes [53]. They also rarely include emerging pollutants associated with specialized atmospheres or furnace designs, both of which are critical for accurate nanomaterial assessment.

Moreover, because SACs rely on very small quantities of active metals, conventional databases are not well-suited to capture subtle but significant flows such as atomic leaching, surface desorption, or micro-level carrier degradation [55]. As a result, inventory modeling for SACs often requires supplementing database information with experimental measurements and targeted literature data.

Table 1. Common data sources for SAC LCI modeling.

Data Source	Type	Advantages	Limitations	Example Use
Experimental measurements	Primary	High accuracy	Limited scale	Lab-scale synthesis emissions
Ecoinvent/GaBi databases	Secondary	Comprehensive coverage	Poor specificity for SACs	Generic process modeling
Process simulations	Modeled	Enables extrapolation	Requires assumptions	Reactor-scale modeling
Hybrid models	Integrated	Combines accuracy and scope	Complex to calibrate	SAC synthesis route analysis

summarizes common data sources used in LCI modeling for SACs, along with their respective advantages, limitations, and typical applications. To enhance accuracy, background processes such as electricity generation or chemical production can still rely on databases. In contrast, SAC-specific core steps, including precursor transformation, support modification, and high-temperature activation, should be supplemented with laboratory or authoritative experimental data. Without this balance, critical micro-scale processes may be oversimplified, leading to biased results.

4.3. Life Cycle Impact Assessment (LCIA)

In the LCIA stage, inventory data are translated into environmental impact categories, which quantify potential consequences for ecosystems, human health, and resources. For SACs, which are materials with structural complexity and multi-stage lifecycle interactions, this step is particularly important, as the choice of LCIA method strongly affects interpretability and comparability.

Commonly used tools include ReCiPe, TRACI, and USEtox. ReCiPe 2016 offers results ranging from midpoint indicators (e.g., GWP, acidification potential, eutrophication potential) to endpoint indicators (e.g., ecosystem damage, human health impacts), making it particularly useful for comparing synthesis routes [77]. TRACI, developed by the U.S. EPA, focuses more on region-specific air quality indicators such as smog formation and ozone depletion, which are particularly relevant for high-temperature pyrolysis that may emit VOCs and NO_x [78]. USEtox, by contrast, centers on human and ecological toxicity based on a fate-exposure-effect framework, making it valuable for assessing risks associated with leached metals or particle release during use and disposal [79]. The overall framework of these LCIA methods as applied to SACs is summarized in Figure 5.

Most LCIA studies on SACs remain focused at the midpoint level, primarily because such indicators correspond more directly to energy consumption, resource extraction, and emissions [80]. However, endpoint-level indicators, such as long-term impacts on ecosystem services or resource scarcity, are rarely considered [77], leaving an incomplete picture of the real-world impacts of SACs.

Compared with conventional catalysts, SACs often exhibit cross-stage coupling of environmental burdens: pollutants may arise not only during synthesis but also during precursor refinement, in-use metal leaching, and oxidative regeneration [81]. This distributed profile complicates attribution, making single-category analyses prone to bias. Furthermore, while SACs typically release only trace amounts of metals during use, their environmental persistence and toxicity remain insufficiently explored [82], introducing substantial uncertainty into LCIA results. Addressing these gaps requires explicit uncertainty analysis and sensitivity checks [75], alongside expanding indicator coverage to include factors like metal migration risks and by-product toxicity.

4.4. Interpretation and Its Role in SAC Design

The interpretation phase of the LCA translates environmental assessment results into actionable design and optimization strategies. For SACs, this step is critical not only to summarize performance across environmental indicators but also to identify hotspots, explore interconnections among lifecycle stages, and guide targeted improvements in materials and processes [83].

Because SAC syntheses often involve complex precursors and diverse synthesis conditions, the resulting environmental hotspots can vary significantly across systems. Interpretation that combines performance metrics with environmental outcomes provides a more balanced perspective. For example, when LCAs reveal that the production of precious-metal precursors dominates the environmental burden, this can motivate the search for non-precious alternatives [67]. Similarly, sensitivity analyses frequently identify pyrolysis temperature and electricity consumption as key influencing parameters. Reducing the pyrolysis temperatures by several hundred degrees, or switching to low-carbon power sources, can significantly decrease GWP with minimal impact on catalytic performance [84,85], thereby supporting the development of low-temperature synthetic routes.

Ultimately, the interpretation phase establishes a feedback loop of design-assessment-redesign, turning LCA from a passive accounting tool into a proactive driver of sustainable catalyst innovation. This iterative role enables SAC development to move beyond single-performance optimization and toward a more integrated framework that balances efficiency, durability, and environmental responsibility.

5. Prospects and Limitations

5.1. Prospects

To advance the systematic application of LCA in the field of SACs, it is essential to construct a framework guided by the principles of green design. Such a framework should not only quantify the environmental burdens across the entire lifecycle of SACs but also act as feedback for catalyst development, providing direction for sustainable design and practical deployment. Drawing on the ISO 14040 series standards as well as existing research experience, three main perspectives can be emphasized.

(I) Green design should intervene from the very beginning of SAC development. Raw material acquisition, synthesis pathways, and other potential environmental burdens need to be considered at the design stage, not just after materials are synthesized. When LCA is integrated at this early stage, design, evaluation, and optimization can form a closed-loop system. This integration ensures that sustainability targets become proactive guiding principles rather than retrospective summaries [86].

(II) The diversity of SAC application scenarios necessitates a modular approach to lifecycle modeling, as the environmental burden of SACs vary considerably across reaction conditions and usage patterns. If every evaluation were to construct models from scratch, efficiency would be low and comparability across studies would be lost. A more practical strategy is to divide the lifecycle into common modules, such as raw material acquisition, catalyst synthesis, operational application, and end-of-life management [87,88]. These modules can then serve as semi-independent sub-models that can be flexibly combined depending on the specific study. Such modularity enhances comparability, reduces redundancy, and enables LCA frameworks to adapt more effectively to diverse evaluation needs.

(III) A more holistic perspective requires linking environmental assessment with technical maturity and economic feasibility. SAC research should not only ask whether a material is environmentally “green”, but also whether it can be produced at scale and whether it is economically viable. Combining LCA with Technology Readiness Level (TRL) and Techno-Economic Analysis (TEA) enables a more balanced evaluation [89,90]. This integrated approach allows researchers to distinguish between catalytic systems that are promising only in theory and those that may realistically advance toward industrial deployment.

In the long run, LCA can evolve into a tool that supports decision-making at every stage of catalyst development. It can help researchers factor in environmental considerations during design, provide feedback during process optimization, and eventually embed “green” into every decision node. Achieving this goal requires LCA itself to advance in parallel with technological progress. Digital tools such as machine learning and computational modeling can help fill data gaps, identify key parameters, and improve both sensitivity and predictive power when experimental data are limited [91,92]. At the same time, open-access data platforms and standardized reporting practices can enhance collaboration across institutions and ensure methodological consistency. Policy incentives, such as environmental regulations or green funding mechanisms, can provide external momentum for the practical application of LCA. Together, these developments will drive SACs toward a genuinely sustainable design paradigm, integrating high performance with environmental responsibility in future manufacturing systems.

5.2. Limitations

Despite these promising prospects, the current application of LCA in SAC research still faces several substantial limitations. The most critical challenge lies in data scarcity. SACs are structurally complex, with diverse synthesis routes and atomic-level construction processes that are difficult to represent accurately within existing databases [93]. As a result, LCA models often rely heavily on assumptions, generalized parameters, or indirect estimates, which reduces the reliability and applicability of results.

Another major limitation is the absence of standardized definitions for functional units and system boundaries. Different studies often employ distinct evaluation frameworks, making their results difficult to compare [94]. For instance, one study may adopt cradle-to-gate boundaries, whereas another may employ cradle-to-grave boundaries. Similarly, one may define functional units as “per kilogram of hydrogen produced,” while another uses “per mole of pollutant removed”. Without harmonization, LCA outcomes cannot form a coherent and comparable knowledge base for guiding SAC development.

A further limitation is the static nature of most existing LCA models. SAC technology pathways and synthesis methods are evolving rapidly, but conventional LCA frameworks tend to capture only fixed snapshots of environmental performance. This makes it difficult to reflect the dynamic changes in environmental burdens associated with technological innovation.

Perhaps most importantly, LCA is still often treated as a supplementary analysis applied after materials are developed, rather than as an integral tool that guides the research and design process from the outset. This reactive role weakens the potential of LCA to influence early-stage decisions, where its feedback could be most impactful.

Overcoming these limitations requires establishing tailored assessment standards, developing specialized databases for advanced materials such as SACs, and creating dynamic and updatable assessment tools. Only by adapting LCA to the specific challenges and evolving needs of SAC research can it fulfill its role as a genuine driver of sustainable catalyst innovation. Sustainable progress in SACs will therefore depend not only on breakthroughs in catalytic performance but also on the parallel advancement of evaluation systems that can keep pace with these innovations.

6. Conclusions

This review has systematically examined the environmental challenges and green design pathways of SACs from a lifecycle perspective. By emphasizing the integration of LCA into SAC research, it highlights both the feasibility and the necessity of using LCA as a guiding framework for sustainable catalyst development.

By examining the principles, applicability, and practical implementation of LCA as well as its role within green design frameworks, this review proposes an approach that embeds environmental feedback into material screening and synthesis optimization. This shifts the role of LCA from a retrospective assessment tool toward an active driver of sustainable catalyst innovation. In this regard, LCA serves as a rational design compass, linking catalyst architecture with sustainability outcomes. By integrating environmental feedback into material screening, LCA can help identify the optimal balance between performance and environmental responsibility, thus promoting the rational design of next-generation SACs.

LCA possesses the capacity not only to identify environmental burdens frequently overlooked in traditional performance evaluations but also to serve as an indispensable instrument for constructing truly sustainable catalytic systems. Looking forward, the deeper integration of LCA with high-throughput screening, multi-dimensional optimization, and policy-driven incentives is likely to form the critical pathway for SACs to achieve green transition and industrial deployment.