Catalyst Development for Dry Reforming of Methane and Ethanol into Syngas: Recent Advances and Perspectives

Abstract

Dry reforming of methane and ethanol is a promising catalytic process for the conversion of carbon dioxide and hydrocarbon feedstocks into synthesis gas (H₂/CO), which serves as a key platform for the production of fuels and chemicals. Over the past decade, substantial progress has been achieved in the design of catalysts with enhanced activity and stability under the demanding conditions of these strongly endothermic reactions. This review summarizes the latest developments in catalyst systems for DRM and EDR, including Ni-based catalysts, perovskite-type oxides, MOF-derived materials, and high-entropy alloys. Particular attention is given to strategies for suppressing carbon deposition and preventing metal sintering, such as oxygen vacancy engineering in oxide supports, rare earth and transition metal doping, strong metal–support interactions, and morphological control via core–shell and mesoporous architectures. These approaches have been shown to improve coke resistance, maintain metal dispersion, and extend catalyst lifetimes. The review also highlights emerging concepts such as multifunctional hybrid systems and innovative synthesis methods. By consolidating recent findings, this work provides a comprehensive overview of current progress and future perspectives in catalyst development for DRM and EDR, offering valuable guidelines for the rational design of advanced catalytic materials.

1. Introduction

Global challenges related to climate change, growing energy demand, and the depletion of fossil resources are driving the search for sustainable and environmentally friendly energy production methods. Fossil fuels oil, coal, and natural gas still dominate the global energy mix, accounting for over 80% of total consumption [1]. However, their intensive use is associated with substantial greenhouse gas emissions, particularly carbon dioxide (CO₂), which exacerbates anthropogenic impacts on the Earth’s climate system [2,3]. In response to these pressing issues, the Paris Agreement was adopted in 2015 with the aim of limiting the rise in global average temperature to well below 2 °C, while pursuing efforts to restrict it to 1.5 °C by 2100 [4,5]. Achieving these goals requires the development and implementation of technologies capable of simultaneously reducing carbon emissions and ensuring a stable energy supply. In this context, carbon-neutral processes that combine environmental compatibility with economic viability have gained particular importance.

One such strategic direction involves the production of synthesis gas (syngas), a versatile intermediate consisting of carbon monoxide and hydrogen. Syngas serves as a key feedstock for the synthesis of ammonia, methanol, liquid hydrocarbons (including synthetic diesel and kerosene), and is also widely utilized in the production of olefins and aromatic compounds [6,7,8]. The current distribution of syngas utilization worldwide is presented in Figure 1.

According to literature sources, the global annual consumption of syngas is approximately 6000 PJ, representing about 2% of total primary energy demand [10]. Its primary use is concentrated in the chemical industry, with approximately 40% allocated to ammonia synthesis, 25% to methanol production, and about 15% to Fischer-Tropsch synthesis for generating liquid fuels [11]. The remaining portion is utilized in energy generation (10%) and in the production of organic compounds (~5%) such as plastics, solvents, and alcohols.

Traditionally, syngas is produced via steam methane reforming (SMR), partial oxidation (POX), or autothermal reforming (ATR). SMR is the most commonly used method, offering a high hydrogen yield (H₂/CO ≈ 3), but it suffers from high energy demand due to the need for superheated steam (>800 °C) and generates significant CO₂ emissions [12]. Moreover, SMR requires extensive feedstock pretreatment to remove sulfur compounds and the use of highly durable materials to withstand harsh reaction conditions [13]. These limitations have driven interest in alternative methods, particularly dry reforming of methane (DRM) and dry reforming of ethanol (EDR), where carbon dioxide is used as the oxidant.

The DRM process, first reported by Fischer and Tropsch in 1928, involves the reaction of methane with CO₂ to form syngas with a near-stoichiometric H₂/CO ratio of approximately 1:1 (CH₄ + CO₂ → 2CO + 2H₂, ΔH° = +247 kJ/mol) [14]. Although the H₂/CO ratio from DRM (1:1) is lower than the optimal value for Fischer-Tropsch synthesis (2:1), the resulting syngas can still be adjusted for downstream applications. In addition to its thermodynamic viability, DRM presents environmental advantages through the simultaneous utilization of two potent greenhouse gases CH₄ and CO₂, making it highly attractive within the framework of carbon circularity and green chemistry [15].

However, practical implementation of DRM requires elevated temperatures (>700 °C) due to the high bond dissociation energies of C–H in methane and C=O in carbon dioxide, which introduces several challenges such as carbon deposition (coking), sintering of active sites, and catalyst deactivation [16,17].

Of additional interest is the EDR, in which ethanol reacts with CO₂ to produce syngas according to the reaction: C₂H₅OH + CO₂ → 3CO + 3H₂. This process offers multiple advantages. First, ethanol is a renewable feedstock derived from biomass, which contributes to reduced dependence on fossil fuels [18]. Second, the use of CO₂ as the oxidant allows for integration into carbon capture and utilization (CCU) schemes. Third, the resulting H₂/CO ratio of 1 is ideal for producing high-energy-density fuels and value-added chemicals [19]. Additionally, ethanol exhibits a lower C–C bond activation energy compared to methane, enabling operation at milder temperatures (300–600 °C). Despite these advantages, both DRM and EDR processes face catalyst-related challenges. In the case of DRM, catalyst stability against coking and thermal degradation remains a critical concern, especially under prolonged operation [20,21,22]. For EDR, the focus lies on the development of highly active and stable catalysts capable of withstanding side reactions such as ethanol dehydration, cracking, and polycondensation [22,23].

This review aims to systematize recent strategies in the design of catalytic systems for DRM and EDR processes. Special emphasis is placed on Ni-based and bimetallic catalysts, as well as promising support materials such as perovskites, zeolites, and metal–organic frameworks (MOFs). The article provides a comparative analysis of approaches to enhancing catalytic activity and stability, strategies for mitigating carbon deposition, the role of promoters, and key thermodynamic and kinetic aspects of the reactions. A unified examination of DRM and EDR allows for the evaluation of their respective advantages and limitations and offers guidance for future research and industrial deployment within the context of sustainable energy and chemical production.

2. Dry Reforming of Methane

DRM is considered a promising technology for simultaneously converting two major greenhouse gases, CH₄ and CO₂, into synthesis gas (a mixture of H₂ and CO) with a near-stoichiometric H₂/CO ratio of 1:1. Compared to conventional reforming methods such as SMR and POM, DRM offers distinctive environmental and thermodynamic advantages. While SMR requires high steam input and produces excessive hydrogen (H₂/CO ≈ 3), and POM demands pure oxygen and suffers from heat management issues, DRM avoids water consumption, utilizes CO₂ directly as an oxidant, and aligns well with Fischer-Tropsch synthesis requirements [2]. The term “dry” in DRM reflects the replacement of water with CO₂ as the oxidizing agent. With renewable energy sources, DRM can become a carbon-neutral process, contributing to the circular carbon economy [24,25].

Thermodynamically, DRM is a strongly endothermic reaction (CO₂ + CH₄ → 2CO + 2H₂, ΔH° = +247 kJ/mol), requiring temperatures above 700 °C to achieve significant conversions [26]. However, these high temperatures also promote side reactions such as methane decomposition, Boudouard reaction, and carbon monoxide disproportionation, leading to coke formation and catalyst deactivation [27].

Table 1. Main and side reactions occurring in the DRM process.

No	Reaction Name	Equation	ΔH° 298k (kJ/mol)
1	Dry reforming of methane	CO2 + CH4 → 2CO + 2H2	+247.0
2	Reverse Water-Gas Shift reaction	CO2 + H2 → CO + H2O	41.0
3	Boudouard reaction	2CO → C + CO2	−171.0
4	Decomposition of methane	CH4 → C + 2H2	75.0
5	Carbon monoxide reduction	CO + H2 → C + H2O	−131.3
6	Hydrogenation of CO2	CO2 + 2H2 → C + 2H2O	−90.0

summarizes the main and side reactions in DRM and their enthalpy changes [28,29].

Although DRM suffers from coke formation due to side reactions such as methane decomposition and the Boudouard reaction, several carbon-removal mechanisms can mitigate this challenge. Notably, deposited carbon can be partially gasified through reactions such as C + H₂O → CO + H₂ and oxidized via C + O₂ → CO₂ or CO, which help regenerate active sites and prolong catalyst life [17]. Despite these challenges, DRM continues to attract attention due to its dual benefit of greenhouse gas mitigation and syngas production. As shown in Figure 2, the number of publications related to DRM has been steadily increasing over the past decade, reflecting the growing scientific and industrial interest.

2.1. Nickel-Based Catalysts: Functionalization of Catalyst Supports

Despite significant progress in catalyst design, industrial implementation of nickel-based systems remains hindered by their rapid deactivation, primarily due to coke formation and sintering of the active metal phase. Recent studies (2023–2025) have demonstrated that deliberate functionalization of catalyst supports is a key strategy to mitigate these challenges, providing improved activity and long-term stability under harsh reaction conditions [24,30].

Zeolites can effectively stabilize nickel nanoparticles. SSZ-13 (CHA) features 8-membered-ring windows (~0.38 nm) and internal cages (~0.67–1.0 nm). However, 2–3 nm Ni nanoparticles reside predominantly on the external surface of the crystals and in mesopores formed during synthesis/post-treatment, as the micropores are too small to host them. Lanthanum doping of SSZ-13 introduces additional Brønsted acid sites that act as anchoring points for Ni precursors and strengthen metal–support interactions, promoting highly dispersed surface Ni. The zeolitic framework ensures efficient transport of reactants and products to active sites, while a hierarchical pore network provides additional stabilization. This synergy combining high Ni dispersion with improved site accessibility reduces carbon deposition by up to ~60% compared with conventional oxide supports [31,32].

Recent studies confirm that Ni-based zeolite catalysts remain a viable route for DRM: Ce-promoted Ni/SSZ-13 (CHA) exhibits enhanced coking resistance and stability, while interzeolite transformation enables CHA-type nickel silicate zeolites (Ni-CHA) with high activity under DRM conditions [33,34].

Among oxide-based supports, particular attention has been devoted to ZrO₂ systems promoted with cerium oxide [35]. The introduction of 5 wt.% CeO₂ into Ni/ZrO₂ significantly enhances resistance to coke formation. This improvement is primarily associated with a twofold increase in oxygen vacancy concentration, as confirmed by Raman spectroscopy. Oxygen vacancies are critical for CO₂ activation and for oxidizing carbonaceous intermediates. The promotional effect of CeO₂ stems from its ability to undergo redox cycling between Ce³⁺ and Ce⁴⁺, facilitating continuous regeneration of the catalyst surface. These vacancies enable CO₂ dissociation to form reactive O* species, which oxidize CH_x fragments into CO, thereby preventing the accumulation of stable graphitic coke. As a result of this synergy, the Ni/CeO₂-ZrO₂ catalyst maintains high activity (CH₄ conversion >85%, CO₂ conversion >90%) over 500 h of continuous operation at 800 °C under a gas hourly space velocity (GHSV) of approximately 39,000 mL·gcat⁻¹·h⁻¹ without significant deactivation.

The authors [36] propose enhancing the stability of Ni-based catalysts through the functionalization of supports with nanomaterials possessing controlled oxygen mobility. The incorporation of cobalt into Ni/ZrO₂ leads to the formation of Ni-Co-O clusters, which intensify redox cycling by enabling rapid oxygen transfer. In situ XRD and EXAFS analyses confirmed dynamic oxygen redistribution between the support and active phase, effectively suppressing the sintering of Ni particles (with sizes maintained below 5 nm after 100 h). It was shown that Co-activated oxygen vacancies in ZrO₂ accelerate carbon gasification via CO₂ according to the reaction: C + O* → CO. The high mobility of O²⁻ ions across the Ni/ZrO₂ interface prevents the accumulation of stable graphitic carbon. As a result, the coke content was reduced by 55% compared to unmodified Ni/ZrO₂, while CH₄ and CO₂ conversions remained above 85% over 300 h of continuous operation at 800 °C under a WHSV of 18,000 mL·g⁻¹·h⁻¹.

An alternative approach involves the use of complex oxide systems, such as CaFe₂O₄ [37]. Investigations of this material as a support for nickel catalysts (15 wt.% Ni) have demonstrated its high efficiency in the DRM process. Under optimized reaction conditions (832.5 °C, CO₂/CH₄ ratio = 0.96, and gas hourly space velocity of 35,000 h⁻¹), conversions of CH₄ and CO₂ reached 85% and 88%, respectively, with corresponding H₂ and CO yields of 77.8% and 75.7%. Notably, despite the formation of carbon deposits confirmed by TGA and TEM analyses, the 15% Ni/CaFe₂O₄ catalyst exhibited no signs of deactivation after 20 h of continuous operation. This behavior is attributed to a dynamic equilibrium between carbon deposition and its gasification by surface oxygen species provided by the Ni/CaFe₂O₄ support. Such a “self-cleaning” mechanism represents a key advantage of this catalytic system.

Natural materials have attracted increasing attention as cost-effective and environmentally benign supports for nickel-based catalysts [38]. Diatomites subjected to plasma etching exhibit a unique hierarchical porous architecture that promotes effective dispersion of the nickel phase and enhances mass transport. Treatment with low-temperature Ar/H₂ plasma generates mesopores ranging from 5 to 15 nm and increases the specific surface area up to 320 m²/g. Studies have demonstrated that a NiO-Co₃O₄/diatomite catalyst with 5–15 nm mesopores achieves a CH₄ conversion of 89% at 850 °C at a volume rate of 1000 h⁻¹, outperforming systems based on synthetic γ-Al₂O₃ supports. The key factor underlying the enhanced activity is the synergy between iron-containing impurities in the diatomite and cobalt, which leads to the formation of catalytically active Fe-Ni-Co alloys. These alloys exhibit improved resistance to coking due to their modified surface electronic properties.

Another natural material with promising characteristics is acid-treated tripolite [39]. Treatment with sulfuric acid (1 M H₂SO₄) selectively removes aluminosilicate impurities, generating a mesoporous structure with pronounced Brønsted acidity. These acid sites enhance the interaction between nickel particles and the support (SMSI—Strong Metal-Support Interaction), thereby reducing the catalyst deactivation rate by approximately 20%. The modified tripolite not only provides structural stabilization of Ni particles but also participates in CO₂ activation, promoting in situ oxidation of carbonaceous species. This effect is particularly important for ensuring the long-term operational stability of the catalyst under dry reforming conditions.

Overall, the functionalization of catalyst supports offers broad opportunities for developing highly stable Ni-based catalysts for dry reforming of methane. Current strategies encompass the use of microporous zeolites with tunable acidity, oxide systems promoted with rare earth elements, and modified natural materials with hierarchical porosity. The key mechanisms responsible for improved stability include spatial confinement of nickel particles, enhanced metal-support interaction, increased oxygen mobility, and in situ oxidation of carbon deposits. Future research should focus on elucidating the fundamental interactions between nickel particles and functionalized supports at the atomic level, as well as on developing scalable synthesis methods suitable for industrial implementation. Particular attention should be given to designing composite supports that simultaneously provide high nickel dispersion, efficient oxygen transport, and optimized acid–base surface properties.

2.2. Bimetallic Ni-Based Catalysts

In pursuit of more robust DRM catalysts, extensive research has focused on bimetallic Ni-based catalysts that combine Ni with a second metal. The addition of an appropriate secondary metal can significantly enhance carbon tolerance and catalytic stability, thanks to synergistic effects that modify Ni’s catalytic properties. A variety of bimetallic combinations have been explored, including Ni alloyed with other transition metals (e.g., Co, Fe, Mo, W) as well as with noble metals (e.g., Pt, Ag) or rare-earth promoters (e.g., La, Ce), each offering distinct mechanisms to mitigate deactivation. These bimetallic systems aim to suppress coke formation and prevent Ni sintering simultaneously, thereby prolonging catalyst lifetime under demanding DRM conditions.

Ni–Co catalysts exemplify the benefits of alloying Ni with another transition metal. In bimetallic Ni–Co/γ-Al₂O₃ systems, the formation of a surface Ni–Co alloy plays a crucial role in suppressing carbon deposition and increasing the concentration of active metallic sites, enabling methane conversions approaching thermodynamic equilibrium at 600 °C [40,41,42,43].

Recent studies confirmed that layered-double-hydroxide-derived Ni–Co with an optimized Ni:Co ≈ 5:1 maintained CH₄ and CO₂ conversions above 85% for 200 h, the stability being linked to Ni–Co alloying and the generation of surface bidentate carbonates that accelerate the turnover of carbon intermediates [44].

Incorporating iron into Ni catalysts can engender unique active phases that actively consume deposited carbon. Under DRM conditions, Ni–Fe catalysts may form intermetallic carbides such as Fe₅C₂ that promote CO₂-assisted gasification of carbon. This approach has enabled exceptionally stable performance; for instance, a Ni–Fe composite maintained ~95% CH₄ and CO₂ conversion over 350 h with negligible coke accumulation. Ab initio calculations confirm that the Ni–Fe₅C₂ phase lowers the activation barrier and continuously removes carbon species, thereby preventing deactivation [45].

The integration of molybdenum oxide into nickel-based catalysts [46,47] leads to the formation of several critical phases that significantly influence the catalytic behavior. Molybdenum carbides (Mo₂C, MoC_x) are generated via carburization during catalyst reduction in CH₄/H₂ [48]. The redox cycling between MoO₃ and MoC_x enables efficient carbon removal, reducing graphitic carbon formation by ~30% [49]. The formation of Ni-Mo alloys is commonly observed in Ni-Mo/YSZ systems [50], where Mo stabilizes metallic Ni and improves dispersion. For example, in Ni–Mo/Al₂O₃, the average Ni particle size decreased from 25 nm to 12 nm (Figure 3). Expanding on these findings, a hierarchical Ni–Mo/MgO catalyst sustained >80% conversion for 100 h through in situ Ni–Mo alloying and oxygen vacancies supplied by MgO, which together inhibited sintering and carbon accumulation [46].

Similar benefits arise from other refractory elements. Ni–W catalysts prepared by solid-state grinding exhibited CH₄ and CO₂ conversions of ~58% and 66% over 24 h, with ultrasmall Ni particles, strong Ni–support bonding, and WC phases suppressing coke accumulation [51]. These carbide-related mechanisms align with strategies to develop self-regenerating systems, such as Ni–Mo₂C/CeO₂, which exploit cyclic carburization–oxidation to maintain activity above 95% after 200 h on stream. In situ XRD confirmed that MoC_x phases catalyze CO₂-assisted gasification of carbon, providing autonomous coke removal.

Beyond transition metals, noble-metal additions have proven effective in stabilizing Ni. Even trace amounts of platinum can profoundly influence Ni’s behavior. Pt-decorated Ni/Al₂O₃ prepared by atomic-layer deposition preserved full activity at 650 °C for 48 h, whereas the monometallic analog deactivated rapidly. Mechanistically, Pt facilitated CO₂ activation and diverted carbon into defective filamentous deposits that did not encapsulate Ni [52]. In fact, even inexpensive noble metals like silver can significantly improve Ni catalyst performance. Ni–Ag/MgAlO with Ag:Ni ≈ 1:19 retained ~95% of its initial activity after 26 h at 800 °C by suppressing filamentous coke and mitigating Ni aggregation [53].

Rare-earth-containing bimetallic designs exploit oxygen storage and vacancy chemistry to couple CH₄ activation at Ni with rapid CO₂-derived oxidation of surface carbon. In the study [54], the acyl-ammonia evaporation method was employed to synthesize a series of Ni–M–SiO₂@SiO₂ (M = Ce, Zr, La, Co, Mg), revealing that rare-earth oxides outperform transition metals in enhancing catalytic activity. CeO₂-promoted catalysts achieved the highest CH₄ conversion (57.2% at 600 °C and GHSV 24,000 mL (g_cat·h)⁻¹) at 5 wt.% promoter loading, compared to 47.5% for the unpromoted analog. The 10Ni–1Ce–SiO₂@SiO₂ catalyst with a core–shell architecture outperformed its impregnated counterpart by delivering 18% higher CH₄ conversion and 40% lower carbon deposition after 12 h, attributed to steric barriers restricting Ni growth (<5 nm) and the formation of nickel phyllosilicate structures that stabilize nanoparticles. Increasing calcination from 700 to 900 °C further enhanced strong metal–support interaction (SMSI), resulting in highly dispersed Ni particles (2–3 nm). The fraction of weakly bound NiO, which can easily reduce to larger Ni⁰ particles, was minimized. This stabilization suppresses the formation of agglomerated metallic Ni and thereby lowers the risk of sintering at elevated temperatures. Oxygen vacancies in CeO₂ promoted CO₂ activation and CH_x oxidation, while hierarchical porosity improved mass transfer. Along similar lines, La-modified Ni catalysts generate La₂O₂CO₃ species and abundant oxygen vacancies, which accelerate CO₂ uptake and oxidation of surface carbon [55]. Ce-doped Ni/SSZ-13 further boosted activity by raising the Ce³⁺/Ce⁴⁺ ratio, stabilizing Ni dispersion, and suppressing coking under DRM [56].

Finally, unconventional alloying such as Ni–Zn offers a distinct anti-coking route. A Ni–Zn/SiO₂ catalyst obtained via selective Zn sublimation achieved 88% CH₄ and 95% CO₂ conversion at 750 °C over 50 h, while reducing carbon deposition by an order of magnitude compared to Ni/SiO₂. This was attributed to Ni–Zn interfacial stabilization and the in situ formation of hydroxyl species that continuously gasified surface carbon [57].

CO₂-assisted regeneration of Ni–Zr catalysts. After four DRM cycles, a Ni–Zr catalyst accumulated filamentous (1D) and layered (2D) graphitic carbon that blocked Ni active sites, accompanied by sintering-induced particle growth from 5–10 nm to >50 nm. Regeneration by CO₂ treatment (C + CO₂ → 2 CO) reactivated the surface by gasifying carbon deposits, raising CH₄ conversion from ~40% to ~70% and approaching the initial ~87%. The surface carbon content decreased from 55.4 to 26.4 at.% (XPS), while SEM showed shrinkage of Ni aggregates and effective coke removal. The regenerated catalyst exhibited improved stability in subsequent DRM cycles; notably, residual filamentous carbon did not block the active sites, as evidenced by sustained CH₄ conversion (~45%) even in a partially deactivated state. This CO₂-regeneration approach combines environmental benefit (CO₂ utilization) with operational practicality, offering a viable path toward self-healing, continuous DRM operation [58].

Mechanistic note. Quantum-chemical DFT+U modeling shows that introducing ~5% Y into Ni decreases the barrier for CH₄ dissociation from ≈1.8 to ≈0.9 eV through d-orbital polarization, thereby facilitating C–H bond cleavage. Experiments corroborate a multi-fold increase in CH₄ conversion and reduced progression of CH_x intermediates to graphitic carbon, while EXAFS detects shortened Ni–Y distances (~2.35 Å) and a positive shift in Ni partial charge, both consistent with electronically tuned, more reactive Ni sites [31].

Taken together, these findings delineate a coherent design space for bimetallic Ni catalysts in DRM: (i) alloying with Co or Zn to reshape Ni carbon chemistry and stabilize dispersion; (ii) pairing with carbide-forming Fe, Mo, or W to couple CH₄ activation with continuous CO₂-assisted carbon removal; and (iii) integrating oxygen-storing rare-earth elements (La, Ce) or trace noble metals (Pt, Ag) to unify high activity with coking resistance. By aligning metal–metal synergy with vacancy engineering and support effects, bimetallic Ni systems achieve long-term stability and activity approaching industrial requirements.

2.3. High-Entropy Alloy-Based Catalysts

A particularly promising direction is the application of high-entropy alloys. Catalysts of the Ni-Co-Fe-Cu-Mn/Al₂O₃ type have demonstrated superior coking resistance due to the suppression of carbon diffusion through the crystalline lattice. Testing at 800 °C confirmed long-term stability over 1000 h with less than 3% deactivation. A comparative overview of bimetallic nickel-based catalysts employed in dry reforming of methane is presented in Table 2.

A critical factor determining the coking resistance of Ni-based catalysts in DRM is the nickel particle size. Recent studies have shown that reducing the Ni particle size to the sub-10 nm range significantly decreases the catalyst’s tendency toward graphitization and carbon accumulation. Finely dispersed Ni particles promote methane activation primarily via full dissociation, forming reactive CH_x intermediates that are less prone to polymerization and subsequent growth of graphitic layers. Moreover, the formation of active sites for the nucleation of filamentous and layered graphitic carbon is significantly hindered on small Ni particles.

In particular, Akri et al. [59] demonstrated that atomically dispersed Ni sites almost completely suppress carbon formation, even under prolonged reaction conditions. The authors of [60] showed that decreasing the Ni particle size on La-doped CeO₂ significantly enhances the catalyst’s selectivity and coking resistance.

Han et al. [61] further emphasized the importance of Ni species strongly interacting with the support, showing that so-called “bounded Ni” sites on γ-Al₂O₃, associated with smaller particle sizes, provide enhanced resistance to coking and improved catalytic performance compared to more weakly bound, free-state Ni.

Chen, Phan, and co-workers [62,63] systematically investigated the effect of various preparation methods and established a clear correlation between smaller Ni particles and lower coke deposition. A recent study [64] further confirmed that an optimal fraction of ultra-fine Ni nanoparticles ensures maximum catalytic activity with minimal coking by increasing the energy barrier for graphitization. Achieving high Ni dispersion should be considered a strategically important goal in the development of efficient DRM catalysts, which must be addressed through careful selection of support materials, metal incorporation techniques, and post-synthetic treatments. Thus, bimetallic and promoter-modified Ni-based catalysts have demonstrated substantial progress in addressing the critical challenges of dry reforming of methane namely, coking and sintering. Ni-Co/γ-Al₂O₃ systems achieve methane conversions approaching thermodynamic equilibrium at 600 °C due to the formation of surface Ni-Co alloys that effectively suppress carbon deposition. The integration of MoO₃ results in the generation of carbide phases (Mo₂C) and Ni-Mo alloys, which not only reduce Ni particle size to approximately 12 nm but also facilitate a dynamic redox cycle for carbon gasification. The incorporation of MgO enhances the basicity of the support, thereby increasing CO₂ adsorption and reducing coke formation by up to 70%.

Rare-earth elements such as Ce and Pr profoundly alter the electronic environment of Ni. CeO₂ introduces oxygen vacancies that enable the oxidation of CH_x intermediates, while Y doping lowers the activation energy barrier for CH₄ dissociation from 1.8 eV to 0.9 eV. Innovative strategies such as BN coatings and high-entropy alloys confer long-term catalytic stability by suppressing carbon crystallization and limiting its diffusion through the active phase. A particularly promising direction involves the combination of multiple modifiers (e.g., Ni-Co-Ce/MgO-Al₂O₃), which may yield enhanced synergistic effects. Key objectives for future research include the optimization of synthesis techniques such as acyl ammonia evaporation for core–shell architectures and the in-depth investigation of in situ active site dynamics using EXAFS and DFT modeling approaches.

Table 2. Comparative table of bimetallic nickel catalysts for dry reforming of methane.

Catalyst	Method of Synthesis	Reaction Conditions (T, P)	Conversion (CH4/CO2)	Rate of Coke Formation	Stability (Running Time)	Key Features	Ref
20 wt.% Ni-Ru/CeO2 (NR)	Wet impregnation	450 °C, 1 atm	92/70	Low (TGA: 1.25 mg/g·h)	1 h	Ni dispersion (2.19 nm), oxygen vacancies CeO2, Ru weakens the Ni-C bond	[65]
7 wt.%Ni-3 wt.%Co/SiO2	Sol–gel	750 °C, 1 atm	87/85	Moderate (TGA: 3.5 mg/g·h)	50 h	Ni-Co synergy, mesoporous SiO2 structure, sintering suppression	[66]
15 wt.% Ni-5 wt.%Fe-Al (SCS)	Solution combustion	900 °C, 1 atm	93/94	High (TGA: >10%)	20 h	Ni3Fe alloy formation, NiAl2O4 spinel, deactivation resistance	[67]
2.5 wt.% Ni-2.5 wt.% Co/MgO-Al2O3	Impregnation	700 °C, 1 atm	73/76	-	30 h	Ni–Co synergy, basic MgO–Al2O3 (CO2 activation), NiO–MgO solid solution, MgAl2O4 matrix (anti-sintering)	[68]
15 wt.% Ni-0.5 wt.%Re/MgAl2O4	Wet impregnation	750 °C, 1 atm	79/67	Moderate (TGA: 4.8 mg/g·h)	50 h	Re increases Ni dispersion, reduces carrier acidity	[69]
3.75 wt.% Ni-1.25 wt.%Co/ScCeZr	Solvothermal	700 °C, 1 atm	46.8/60	Low (TGA: 2.5 mg/g·h)	5.5 h	Mixed oxides Sc-Ce-Zr, strong metal-support interaction, isolated O2−	[70]
1.2 wt.% Ni-0.3 wt.%Co/SiO2	Sol–gel	550 °C (light), 1 atm	75/80	Minimum (TGA: 0.8 mg/g·h)	30 h	Photoactivation by hot carriers, selective oxidation *CHO→ CO	[71]

Notes: *CHO → CO indicates the selective oxidation of the formyl group (–CHO) into carbon monoxide (CO) during photoactivation by hot carriers.

Table 2. Comparative table of bimetallic nickel catalysts for dry reforming of methane.

Catalyst	Method of Synthesis	Reaction Conditions (T, P)	Conversion (CH4/CO2)	Rate of Coke Formation	Stability (Running Time)	Key Features	Ref
20 wt.% Ni-Ru/CeO2 (NR)	Wet impregnation	450 °C, 1 atm	92/70	Low (TGA: 1.25 mg/g·h)	1 h	Ni dispersion (2.19 nm), oxygen vacancies CeO2, Ru weakens the Ni-C bond	[65]
7 wt.%Ni-3 wt.%Co/SiO2	Sol–gel	750 °C, 1 atm	87/85	Moderate (TGA: 3.5 mg/g·h)	50 h	Ni-Co synergy, mesoporous SiO2 structure, sintering suppression	[66]
15 wt.% Ni-5 wt.%Fe-Al (SCS)	Solution combustion	900 °C, 1 atm	93/94	High (TGA: >10%)	20 h	Ni3Fe alloy formation, NiAl2O4 spinel, deactivation resistance	[67]
2.5 wt.% Ni-2.5 wt.% Co/MgO-Al2O3	Impregnation	700 °C, 1 atm	73/76	-	30 h	Ni–Co synergy, basic MgO–Al2O3 (CO2 activation), NiO–MgO solid solution, MgAl2O4 matrix (anti-sintering)	[68]
15 wt.% Ni-0.5 wt.%Re/MgAl2O4	Wet impregnation	750 °C, 1 atm	79/67	Moderate (TGA: 4.8 mg/g·h)	50 h	Re increases Ni dispersion, reduces carrier acidity	[69]
3.75 wt.% Ni-1.25 wt.%Co/ScCeZr	Solvothermal	700 °C, 1 atm	46.8/60	Low (TGA: 2.5 mg/g·h)	5.5 h	Mixed oxides Sc-Ce-Zr, strong metal-support interaction, isolated O2−	[70]
1.2 wt.% Ni-0.3 wt.%Co/SiO2	Sol–gel	550 °C (light), 1 atm	75/80	Minimum (TGA: 0.8 mg/g·h)	30 h	Photoactivation by hot carriers, selective oxidation *CHO→ CO	[71]

Notes: *CHO → CO indicates the selective oxidation of the formyl group (–CHO) into carbon monoxide (CO) during photoactivation by hot carriers.

2.4. Perovskite-Based Catalysts

Perovskite-based catalysts offer unique advantages in the DRM, effectively addressing key limitations of conventional systems, such as carbon deposition, thermal instability, and high energy demand. Their structural and functional versatility including tunable composition, oxygen mobility, and metal synergy—opens new pathways for sustainable conversion of greenhouse gases into synthesis gas [72,73,74].

Lanthanum-based perovskites, such as LaNiO₃ and La₂NiO₄, exhibit exceptional resistance to carbon accumulation. Their intrinsic surface properties neutralize acidic sites responsible for methane cracking, while high lattice oxygen mobility facilitates the oxidation of carbon deposits [75,76,77]. For instance, LaNiO₃ synthesized via nanocasting using an SBA-15 mesoporous template was shown to deliver about 90% CH₄ and CO₂ conversion at 800 °C in temperature-programmed tests, while at 700 °C it maintained stable conversion for 48 h without detectable coke, consistent with the decomposition of LaNiO₃ into Ni-based phases under reaction conditions [77]. The introduction of cerium into LaNi_0.75Ce_0.05 Zr_0.20O₃/8MgO-SiO₂ enhances metal-support interactions and further reduces carbon deposition [78,79,80].

Elemental substitution in A/B sites (e.g., La, Ca, Co, Ti) enables the optimization of physicochemical properties. Replacing La with Ca in La_1−xCa_xNiO₃ increases basicity and CO₂ adsorption capacity, while incorporating elements such as Co or Ti into La–Ni perovskites enhances oxygen mobility and stabilizes the lattice, thereby improving redox activity [81,82].

The co-presence of Ni and Cu at the B-site generates bimetallic active centers, wherein Ni promotes CH₄ dissociation and Cu facilitates CO₂ activation. This synergy results in CH₄ conversion exceeding 83% and CO selectivity above 97% at 700 °C [83,84].

Ni-Fe diamond-shaped nanoparticles produced via atomic layer deposition exhibit enhanced activity attributed to a favorable spontaneous alloying energy of −0.43 eV. Perovskite-based catalysts also display superior thermal stability compared to conventional systems. Nanostructured perovskites such as LaNiO₃ and SrZrRuO₃ retain structural integrity at temperatures up to 900 °C. LaNiO₃ synthesized via auto-combustion shows a specific surface area of 150 m²/g, which prevents sintering of Ni nanoparticles (15–20 nm) even during extended operation [85]. SrZrRuO₃ prepared via solid-state synthesis exhibits a space-time yield of 500 L·h⁻¹·g·cat⁻¹ at 900 °C, owing to the formation of a thermally stable perovskite matrix [86]. A promising direction involves the integration of DRM with solar energy. LaCu_0.5Ni_0.5O₃ remains catalytically active at 450–750 °C, which is 200–300 °C lower than conventional Ni/Al₂O₃ catalysts. This reduction in reaction temperature decreases energy consumption to 1.61 MJ/kg of syngas, compared to 11.5 MJ/kg, leading to an 86% reduction in carbon footprint.

The reversible formation of oxygen vacancies (V₀⁻) in perovskites contributes to the regeneration of active sites. For instance, LaCu_0.5Ni_0.5O₃ was shown to achieve 98% CO₂ conversion per cycle in a two-step process involving partial methane oxidation followed by CO₂ reduction. An overview of DRM-active perovskite catalysts is shown in

Table 3. Comparative table of perovskite catalysts for DRM.

Catalyst	Method of Synthesis	Process Conditions (T, GHSV)	Feed Gas Ratio	Conversion, % (CH4/CO2)	Key Features	Ref
La2NiO4	Sol–gel	850 °C, 24,000 h−1	CH2:CO2 = 1:1	83/92	High dispersion metallic Ni0, coke reduction	[72]
La0.9Ce0.1NiO3	Pechini method	700 °C, 300 l·h−1·gcat−1	10% CO2/10% CH4/80% Ar	80/71	Oxygen vacancies and electron-hole pairs	[73]
LaNiO3	Sol–gel	800 °C, 15 l·h−1·gcat−1	CH2:CO2 = 1:1	97/95	High resistance to coke, Ni dispersion	[74]
LaZrxNi1-xO3	Citrate method	700 °C, 58L/(g.h.)	25/25/50 CH4/CO2/He)	77/86	Resistance to sintering, activity at extreme temperatures	[75]
LSCrN@NF	Self-combustion method	750 °C, 10 mL min−1	45% CH4–45% CO2–10% N2	80/83	Optimized basicity, increased CO2 adsorption	[76]
LaNi0.8Cu0.2O3	Sol–gel	700 °C, 250 l·h−1·gcat−1	CH4:CO2:Ar = 10:10:1	83/85	Low activation energy, Cu-Ni synergy	[78]
10 wt % Ni/LaAlO3	Impregnation	700 °C, 1.2 10−4 cm3/(h g)	CH2:CO2 = 1:1	87/86	Strong interaction of active centers with the carrier	[79]
2%Co- La0.2Ca0.8NiO3-ZrO2	Co-precipitation method	700 °C, 42,000 h−1	CH4: CO2:N2(Ar) = 1:1:1	88/90	Metal-carrier interaction and metal synergy	[81]
La0.8Sm0.2NiO3	Citrate sol–gel method	750 °C, 200,000 h−1	Ar:CH4:CO2 = 2.5:1.5:1	40/78	Reduced ordering/crystallinity of deposited coke	[87]

.

Metal synergy in bimetallic (Ni-Cu, Ni-Co) and ternary (Co-Ni-Fe) systems enhances the activation of CH₄ and CO₂, resulting in high conversion and selectivity. The expression of Ni nanoparticles in structured formulations such as PrBaMnCoNi-15-Fe effectively prevents sintering of active sites, maintaining catalytic activity even at temperatures as high as 900 °C. Modification of oxygen vacancies through the incorporation of Ce, Sr, or Ca increases the oxidative capacity of the catalysts and effectively suppresses carbon accumulation. Hybrid architectures with supports (e.g., SiO₂, Al₂O₃) contribute to the stabilization of dispersed metal nanoparticles, preventing their aggregation. Additionally, the low-temperature activity of Cu-containing perovskites (450–750 °C) reduces process energy requirements, facilitating integration with renewable energy sources.

A key factor influencing the activity of perovskite-based catalysts is the controlled exsolution of metal nanoparticles from the perovskite lattice under reducing conditions [88,89,90]. During the exsolution process, B-site metals (such as Ni, Fe, or Co) diffuse toward the surface of the oxide matrix, forming uniformly distributed and strongly embedded nanoparticles. This approach offers excellent resistance to sintering, carbon deposition, and structural degradation, thereby significantly improving catalyst stability compared to conventional methods of active metal incorporation. For instance, it has been demonstrated that Ni nanoparticles exsolved from La_0.9Ce_0.1Fe_0.95Ni_0.05O₃ significantly enhance methane conversion, reduce carbon accumulation, and maintain long-term stability for over 120 h of operation [91,92,93].

Studies [94,95,96] emphasize the role of oxygen vacancies and redox cycling in regenerating exsolved active sites, further confirming the potential of such catalysts in DRM. Recent research indicates that the rational design of perovskite materials capable of in situ exsolution enables the development of catalysts with a high density of active sites, strong anchoring of metal nanoparticles, and resistance to aggregation under high-temperature DRM conditions.

The synergistic effect of exsolved metal species and lattice oxygen facilitates the activation of CH₄ and CO₂, while simultaneously promoting continuous oxidative removal of surface carbon deposits. Thus, the exsolution of metal nanoparticles from the perovskite lattice opens new avenues for the development of advanced catalysts for DRM. Recent studies have demonstrated that such materials effectively address the key challenges of the DRM process: they suppress carbon formation, exhibit strong resistance to thermal degradation, and improve the overall energy efficiency of the reaction. Due to their high catalytic activity, resistance to deactivation even after more than 100 reaction cycles, and ability to operate at intermediate temperatures, perovskite-based catalysts are emerging as a foundation for scalable and economically viable DRM technologies. Future research directions include the optimization of perovskite compositions, the development of cost-effective and environmentally friendly synthesis methods, and in-depth investigation of their long-term stability under industrial conditions. Thus, perovskite-based catalysts have the potential to play a pivotal role in the development of sustainable greenhouse gas conversion technologies, contributing to emissions reduction and the transition toward a closed carbon cycle in the energy and chemical sectors. These innovations directly address the main challenges associated with DRM: coke formation, thermal degradation, and high-energy consumption. The improved resistance of catalysts to deactivation (over 100 cycles) and their ability to operate in the intermediate temperature range offer a promising route toward scalable deployment of the technology. Future research should focus on compositional optimization, long-term stability evaluation, and the development of cost-effective synthesis methods suitable for industrial application. Consequently, perovskite-based catalysts are emerging as a key component in the development of sustainable systems for the conversion of greenhouse gases into synthesis gas.

2.5. MOF-Derived Catalysts

Metal–organic frameworks (MOFs) serve as versatile precursors for catalyst design, enabling the development of systems with controlled morphology, high dispersion of active metals, and strong metal-support interactions. Their unique architecture provides structural tunability and spatial confinement, which are critical for mitigating catalyst deactivation via coking and sintering [97,98,99].

The stability of MOF-derived Ni–MgO@mSiO₂ is attributed to the mesoporous SiO₂ framework and to interfacial M–O–Si linkages that anchor node-derived oxide/metal nanoparticles (Ni–O–Si, phyllosilicate-like) to the support [100]. Physicochemical analysis confirmed strong bonding between metallic centers and the SiO₂ scaffold, effectively preventing Ni particle agglomeration (mean size: 7.2 nm) even at 700–800 °C. The coke formation rate (1.25 mg·g⁻¹·h⁻¹) is reduced sixfold compared to conventional analogs due to the presence of surface OH⁻ groups that react with CH_x intermediates and the mesoporous structure that limits Ni migration. After 60 h of operation, the average Ni particle size increased only to 18.3 nm, while CH₄ conversion remained at 75% at 700 °C.

Mechanistic aspects of MOF-derived catalyst formation at elevated temperatures. Under DRM-relevant temperatures, MOFs do not persist as crystalline frameworks: organic linkers undergo pyrolysis/decarboxylation (≈350–600 °C), while node species reorganize into oxide/metal nanoparticles at positions pre-defined by the original lattice. When the MOF is silicified, subsequent calcination promotes interfacial condensation and the formation of M–O–Si bridges that chemically tether these node-derived nanodomains within the mesoporous SiO₂ network (Ni–O–Si, phyllosilicate-like), thereby limiting particle migration/coalescence and suppressing filamentous carbon. The atmosphere and thermal program govern crystallite size and defect chemistry (e.g., Ce³⁺/oxygen vacancies), which in turn affects coking and stability. This MOF-to-catalyst route differs from the pyrolysis of generic metal–organic precursors by offering a pre-organized distribution of metal centers (high nucleation density), inherited porosity/confinement, and upon silicification, chemical M–O–Si anchoring, yielding smaller, better-tethered nanoparticles and improved DRM stability [64,65,101].

In a related study [65], the Ni-Ce-BTC MOF was synthesized via solvothermal treatment, and after 120 h of operation, the average Ni particle size was still limited to 18.3 nm. Subsequent pyrolysis in different atmospheres (N₂, H₂, CO₂) yielded Ni/CeO₂ catalysts with controlled morphology. The N₂-pyrolyzed sample (N₂-pyr) possessed the smallest Ni (2.19 nm) and CeO₂ (2.78 nm) crystallite sizes, high specific surface area (245 m²/g), and a mesoporous structure. CO₂ pyrolysis resulted in larger Ni particles (13.6 nm) due to oxidation-induced agglomeration. N₂-pyr exhibited minimal coke accumulation (2.88 mg·g⁻¹·h⁻¹), attributed to a high Ce³⁺ fraction (37%) that promoted oxygen vacancy formation for CH_x oxidation, along with the presence of amorphous carbon forming a protective layer around Ni particles. In contrast, CO₂-treated catalysts accumulated up to 65.4 mg·g⁻¹·h⁻¹ of coke due to weak metal-support interactions.

The Ni/CeO₂-M catalyst, derived from a Ce-MOF precursor, demonstrated superior low-temperature performance (400–600 °C) [101]. The CeO₂-M support, synthesized from Ce-MOF, features a nanorod morphology (50 nm diameter) and mesoporosity, leading to a high surface area (22.4 m²/g) and uniform Ni dispersion. The average Ni particle size in Ni/CeO₂-M was 17.2 nm (versus 38.4 nm in Ni/CeO₂-C), as confirmed by TEM and XRD. A higher Ce³⁺ content (28% vs. 24%) and elevated ID/IF2 g ratios in Raman spectra (0.18 vs. 0.16) indicated a greater concentration of oxygen vacancies, which facilitated CO₂ activation. The coke formation rate on Ni/CeO₂-M (1.25 mg·g⁻¹·h⁻¹) was significantly lower than that of Ni/CeO₂-C (7.47 mg·g⁻¹·h⁻¹). Oxygen vacancies enhanced CO₂ dissociation to CO and reactive oxygen species, which oxidized CH_x intermediates and prevented their polymerization.

Strong Ni-CeO₂ interaction and the mesoporous structure of CeO₂-M inhibited Ni migration [102]. After 10 h of reaction, the Ni particle size increased only to 17.9 nm (vs. 39.5 nm for Ni/CeO₂-C). At 550 °C, CH₄ and CO₂ conversions for Ni/CeO₂-M reached 30.8% and 40.1%, respectively (compared to 15.5% and 27.3% for Ni/CeO₂-C). After 10 h, Ni/CeO₂-M showed a 39.6% activity loss, whereas Ni/CeO₂-C experienced a 57.7% decline.

A solvothermal synthesis route (120 °C, 12 h) of MOG-Al-La gel followed by calcination at 750 °C yielded mesoporous LaAlO₃ with high specific surface area (33 m²/g) and small crystallite size (28 nm) [79]. Ni nanoparticles (5.03 nm) were uniformly distributed on the perovskite surface, as confirmed by TEM and XRD. Strong Ni-support interactions suppressed agglomeration even at 700–800 °C. The coke formation rate was 1.25 mg·g⁻¹·h⁻¹, compared to 7.47 mg·g⁻¹·h⁻¹ for the sol–gel-derived counterpart. Oxygen vacancies in LaAlO₃ promoted the oxidation of CH_x intermediates, inhibiting their polymerization. The mesoporous architecture and MSI further limited Ni mobility. After 60 h of reaction, the average Ni particle size increased only to 18.3 nm. At 700 °C, CH₄ and CO₂ conversions reached 75% and 80%, respectively, after 20 h. The H₂/CO selectivity ratio was 0.88, closely matching thermodynamic equilibrium. The catalyst outperformed conventional Ni/Al₂O₃ and Ni/LaAlO₃ systems in both activity and stability [103,104].

The use of Zr-based metal–organic frameworks (UiO-66) enabled the synthesis of catalysts with controlled morphology [105]. Among the series, Ni/ZrO₂-B (prepared by impregnating Zr-MOF with nickel) exhibited the smallest NiO particle size (20.47 nm) and the highest dispersion, as confirmed by XRD and TEM. In contrast, Ni/ZrO₂-A (in situ Ni incorporation) and Ni/ZrO₂-C (post-ZrO₂ formation Ni addition) produced larger NiO particles (23.42 nm and 32.02 nm, respectively). All catalysts exhibited mesopores of ~25 nm, which improved mass transport, and BET surface areas up to 12.93 m²·g⁻¹. Ni/ZrO₂-B exhibited low coke accumulation (3.8 wt% after reaction) owing to abundant oxygen vacancies in the ZrO₂ support that promote CO₂ activation and subsequent oxidation of CHₓ intermediates, as well as strong metal–support interaction (MSI) that limits Ni agglomeration. For comparison, Ni/ZrO₂-A and Ni/ZrO₂-C accumulated 6.9 wt% and 0.7 wt% coke, respectively. After 6 h of reaction, the Ni particle size in Ni/ZrO₂-B reached 16.60 nm, substantially smaller than in Ni/ZrO₂-A (27.64 nm).

Table 4. Key characteristics of MOF-derived catalysts for dry reforming of methane.

Catalyst	Ni Particle Size (nm)	Coke Formation Rate (mg·g−1·h−1)	CH4/CO2 Conversion at 700 °C (%)	Stability (Particle Growth, %)	Specific Surface Area (m2/g)	Key Features	Ref
5.3 wt.%Ni-3.1 wt.% MgO@mSiO2 (MOF-derived)	7.2 → 18.3 (60 h)	1.25 (vs. 7.47 for analog)	96 → 75/75 → 69	+154%	n/a	SiO2 mesopores; OH− groups; Ni–O–Si anchoring (phyllosilicate interphase)	[100]
20 wt.% Ni-Ce-BTC (N2-pyr)	2.19 → 18.3 (120 h)	2.88 (vs. 65.4 with CO2 treatment)	n/a	+740%	245	37% Ce3+, protective carbon layer, high proportion of oxygen vacancies	[65]
4.57 wt.% Ni/CeO2-M	17.2 → 17.9 (10 h)	1.25 (vs. 7.47 for Ni/CeO2-C)	30.8/40.1 (550 °C)	+4%	22.4	CeO2 nanorods, ID/IF = 0.18	[101]
10 wt.% Ni/LaAlO3	5.03 → 18.3 (60 h)	1.25 (vs. 7.47 for sol–gel analog)	75/80	+264%	33	Perovskite structure, oxygen vacancies, mesopores	[79]
13.45 wt.% Ni/ZrO2-B	20.47 → 16.6 (6 h)	3.8 wt.% (vs. 6.9 wt.% for A; 0.7 wt.% for C)	n/a	−19%	12.93	Oxygen vacancies ZrO2, 25 nm mesopores, strong metal-support interaction	[105]

Notes: Coke accumulation (Ni/ZrO₂ series): wt% of coke relative to catalyst mass after reaction (TGA on spent catalysts). Particle growth: percentage increase in Ni particle size over the indicated reaction time (from TEM/XRD).

summarizes the key physicochemical characteristics of these MOF-derived catalysts for dry reforming of methane.

Thus, MOF-derived precursors enable the fabrication of DRM catalysts with high stability and activity. Recent studies on MOF-based catalysts for dry reforming of methane highlight several interconnected approaches aimed at overcoming key process limitations. Morphology control plays a central role: mesoporous structures based on SiO₂, CeO₂, or ZrO₂ not only stabilize active metal nanoparticles by preventing agglomeration but also facilitate mass transport of reactants and products. For instance, the SiO₂ mesopores in Ni–MgO@mSiO₂ create diffusion channels that enhance reactant mobility while simultaneously restricting Ni migration. An important complement to morphological tuning is the generation of oxygen vacancies via the introduction of Ce³⁺/Ce⁴⁺ or Zr³⁺/Zr⁴⁺ species. These defects enhance the oxidative potential of the catalysts by activating CO₂ for the oxidation of CH_x intermediates, reducing the coke formation rate by ~60–80%. In hybrid systems such as LaAlO₃/Ni, oxygen vacancies within the perovskite matrix further stabilize Ni nanoparticles, ensuring long-term catalyst stability even at 700–800 °C. Hybrid materials combining MOF-derived routes with perovskites (e.g., LaAlO₃) or oxides (e.g., MgO) exhibit synergistic properties: perovskites provide thermal robustness, whereas the MOF-derived texture ensures high dispersion of active sites. For example, the Ni/CeO₂-M composite derived from a Ce-MOF integrates the nanorod morphology of CeO₂ with a mesoporous network, achieving 30.8% CH₄ conversion at 550 °C. The low-temperature activity of such systems opens promising avenues for integrating DRM with renewable energy sources, reducing energy consumption by ~40–50% compared with conventional processes operating at 8,001,000 °C. These advances demonstrate that MOF-derived catalysts address coking and sintering while improving the economic and environmental viability of DRM.

3. Ethanol Dry Reforming

3.1. General Aspects of the EDR Process

Ethanol dry reforming has emerged as a promising pathway for the sustainable conversion of renewable ethanol and CO₂ into syngas, with a theoretical H₂/CO ratio of 1:1. Ethanol is an attractive feedstock due to its renewability, low toxicity, ease of handling, and potential for large-scale production from lignocellulosic biomass, municipal solid waste, and other sources [106,107]. Although steam reforming of ethanol has been extensively studied, recent years have witnessed increasing interest in EDR due to its advantages in CO₂ utilization and compatibility with carbon-neutral strategies. Compared to methane, ethanol exhibits easier activation at lower temperatures due to the presence of -OH and -CH₂- functional groups. Thermodynamically, the EDR reaction becomes favorable above 318 °C and is highly endothermic, requiring optimized conditions for effective syngas production [108,109]. Figure 4 illustrates the growing number of publications on EDR between 2015 and May 2025, reflecting the expanding research interest.

The primary EDR reaction is a highly endothermic process. The resulting syngas, with a theoretical H₂/CO molar ratio of approximately 1:1, serves as a versatile precursor for methanol synthesis, higher alcohols, Fischer-Tropsch hydrocarbons, and hydrogen fuel cell applications [110,111,112]. Nevertheless, the EDR process is accompanied by side reactions that reduce selectivity and promote carbon deposition. Common competing reactions include ethanol dehydrogenation to acetaldehyde, subsequent decomposition to methane and CO, methanation, and coke formation (

Table 5. Possible reactions of ethanol dry reforming and their equations.

№	Reaction Name	Equation	ΔH° 298k (kJ/mol)
1	The main reaction of EDR	C2H5OH + CO2 → 3CO +3H2	+296.7
2	Dehydrogenation of ethanol	C2H5OH → CH3CHO + H2	+68.5
3	Decomposition of ethanol	C2H5OH → CO + CH4 + H2	+49.6
4	Acetaldehyde decomposition	CH3COH→ CH4 + CO	−18.9
5	Dry reforming of acetaldehyde	CH3COH + CO2 → 2H2 + 3CO	−186.3
6	Methanation of CO2	CO2 + 4H2 → CH4 + 2H2O	−153.0
7	Methanation of CO	CO2 + 3H2 → CH4 + H2O	−206.2
8	Dry reforming of methane	CH4 + CO2 → 2CO + 2H2	+247.0

). Typical by-products include CH₄, C₂H₄, H₂O, and solid carbon. The overall process stability and yield of target products depend strongly on the catalyst nature and reaction parameters such as temperature, pressure, and reactant ratios.

To enhance the efficiency of EDR, both thermodynamic and kinetic studies have been conducted. For example, [113] used Aspen Plus modeling to demonstrate that the addition of O₂ and H₂O can regulate the H₂/CO ratio and effectively suppress carbon formation. Feeding an O₂/CO₂/ethanol mixture at a molar ratio of 0.2/1/1 at 800 °C yields an H₂/CO ratio of approximately 1, while the introduction of 2 moles of H₂O at 650 °C increases this ratio to around 2. The integration of heat exchangers reduced overall energy consumption by 33–35%, highlighting the advantages of hybrid operating modes.

The kinetic aspects of EDR have also been explored by [114] using a LaCuO₃ catalyst synthesized via the citrate sol–gel method. The authors found that the reaction follows a power-law kinetic model, with reaction orders of 0.64 for C₂H₅OH and 0.26 for CO₂. The activation energy was calculated to be 44.2 kJ/mol. The catalyst exhibited high stability and minimal carbon deposition, as confirmed by SEM and FTIR analyses, making it a promising candidate for scale-up applications.

In summary, despite certain thermodynamic and technological limitations, EDR remains one of the most promising pathways for the sustainable transformation of ethanol and CO₂. Modern strategies involving catalyst modification, optimization of reaction parameters, and the adoption of hybrid approaches (e.g., photothermal activation) pave the way toward stable and energy-efficient syngas production.

3.2. Catalytic Systems for the EDR Reaction

Noble metal-based catalysts (such as Pt, Rh, and Pd) are traditionally considered the most effective systems for reforming processes, including EDR [109,115,116]. These metals exhibit strong capabilities in activating C–C and C–H bonds in reactant molecules while also demonstrating high resistance to carbon deposition. However, their high cost and limited availability significantly hinder their widespread industrial application. This has prompted extensive efforts to identify more affordable and abundant alternatives.

Among the most promising substitutes are transition metals such as Ni, Co, and Cu, which also exhibit notable catalytic activity in reforming reactions [110,117,118]. Nickel, in particular, has gained widespread attention for EDR due to its strong ability to activate ethanol and CO₂ molecules, combined with its relatively low cost and wide availability. Ni-based catalysts are known for their efficient bond cleavage and high yields of desired products [119].

Nevertheless, the application of nickel is accompanied by two key challenges: the tendency of Ni particles to sinter at high temperatures, and the formation of carbon deposits on the catalyst surface, which block active reaction sites [120]. Accelerated coke formation leads to rapid catalyst deactivation, posing one of the main limitations in EDR. Nickel is conventionally supported on γ-Al₂O₃ due to its high surface area and excellent thermal stability, which enable good metal dispersion and moderate metal-support interaction. However, under EDR conditions, the Lewis acid sites on γ-Al₂O₃ promote side ethanol dehydration reactions, forming ethylene, which significantly intensifies coking. The accumulation of dense carbon species on the nickel surface further accelerates catalyst deactivation. Cobalt has also been explored as an alternative active phase due to its effective C–C bond cleavage ability in organic molecules, although its application in EDR remains less investigated. Copper typically shows lower activity than Ni and Co in ethanol activation and is thus used primarily as a promoter or as part of complex mixed-oxide systems.

In summary, while nickel remains an active and cost-effective metal for EDR, its practical application requires overcoming issues of thermal stability and coke formation. This can be addressed through careful optimization of the catalyst support, control over structural features, and the incorporation of promoters to enhance the resistance of Ni-based systems to deactivation.

3.2.1. Influence of the Support on Catalyst Activity and Stability

The physicochemical properties and composition of the support play a crucial role in determining the activity, selectivity, and stability of EDR catalysts. The nature of the support governs the dispersion and state of the deposited nickel particles, as well as the prevalence of side reactions.

High surface area and well-developed porosity are also critical parameters. The use of mesostructured materials such as SBA-15 or KIT-6 allows for uniform distribution of the active phase and reduces the average Ni particle size, thereby minimizing sintering [119]. Furthermore, the catalyst synthesis method strongly influences the support’s defect structure. Techniques such as co-precipitation and sol–gel synthesis can produce nanostructured supports with high surface area and defect density, which improves metal dispersion and may indirectly enhance metal–support interactions rather than strengthening them solely by surface area increase. As a result, the concentration of easily reducible sites and oxygen vacancies responsible for coke oxidation can be significantly increased. In the case of EDR, excessively strong metal–support interaction is not required; a balanced interaction that stabilizes Ni particles while maintaining accessible active sites is more beneficial. For example, in [120], the effect of varying the Al₂O₃ content in the Al₂O₃-(Zr-Yb)O₂ support was demonstrated. The Ni/65AZ catalyst exhibited higher ethanol and CO₂ conversions and greater H₂ and CO yields compared to Ni/35AZ under identical conditions, attributed to a higher concentration of oxygen vacancies and a more stable post-reaction texture.

It has been established that oxide supports with high oxygen mobility significantly suppress coke formation due to the involvement of oxygen vacancies in the oxidation of carbonaceous intermediates. Specifically, the incorporation of CeO₂ or the use of mixed oxides such as CeO₂-ZrO₂ and Ce(La)O_x enhances the oxygen storage and release capacity, thereby mitigating carbon deposition on the catalyst surface [121]. The in situ activated oxygen oxidizes intermediate carbide species (*C → CO) and hydrogen species (*H → OH), thus preventing the growth of carbon deposits. In contrast, acidic supports such as γ-Al₂O₃ promote parallel reactions (e.g., ethanol dehydration), leading to increased coke formation. Consequently, replacing or modifying γ-Al₂O₃ with more inert or basic supports is essential for ensuring the long-term stability of Ni-based catalysts in EDR.

Shi et al. [122] compared synthesis routes for Ni-Ce-Zr catalysts and found that co-precipitation produced smaller Ni particles (<5 nm) and a higher proportion of Ni⁰ (58% vs. 27%, per XPS). This nanodispersed catalyst achieved 65.3% ethanol conversion at 700 °C and demonstrated improved resistance to carbon deposition. Similarly, [123] showed that a hard-templated CoZnO-HT catalyst achieved complete ethanol conversion at 550 °C and stable performance for 40 h, whereas the impregnated CoZnO-C counterpart accumulated acetone as a byproduct and exhibited lower activity. The enhanced performance of CoZnO-HT was linked to its smaller Co particle size and a higher oxygen vacancy concentration (39%). Raman spectroscopy confirmed that coke deposits on CoZnO-HT were mostly amorphous (D/G = 1.52), while CoZnO-C contained more graphitic carbon (D/G = 1.39), accelerating deactivation.

Another effective strategy involves encapsulating the active metal within an inert shell. For instance, the Co@SiO₂ catalyst with a 20 nm silica coating exhibited complete ethanol conversion at 550 °C and no activity loss over 40 h [124]. The silica shell prevented direct contact between metal particles and coke precursors, while the high interfacial oxygen vacancy density (1.03) enhanced in situ carbon gasification. A promising alternative support is the Cu-Ce-Zr mixed oxide with a flower-like morphology (CuCeZr-M) [125]. This catalyst, synthesized via a one-step microwave-assisted method, delivered full ethanol conversion at 750 °C and stable operation for 50 h. Its high mobile oxygen content (28.7% Ce³⁺ per XPS) and low carbon accumulation (<3 wt%, TGA) account for its exceptional stability. The structural and coke-resistance properties of the Ni/xAl₂O₃–(Zr+Ce)O₂ catalyst after the ethanol dry reforming reaction are shown in Figure 5.

Support composition not only affects the rate but also the nature of coke formation. Fionov et al. [126] demonstrated that increasing Al₂O₃ content to 50 mol.% in Al₂O₃-(Zr+Ce)O₂ led to smaller Ni particles (15 nm), stronger metal-support interactions, and nearly complete suppression of coking (mass loss <1% by TGA after 7 h of testing). At lower Al₂O₃ content (5–20%), ordered carbon structures such as nanospheres and thick nanotubes formed, while higher Al₂O₃ content (50–75%) resulted in amorphous carbon and hollow nanotubes. These latter forms did not block active Ni sites, explaining the minimal deactivation rate. Raman spectroscopy confirmed the shift toward more amorphous carbon (increasing ID/IG ratio) with increasing Al₂O₃, whereas samples with low Al₂O₃ content showed prominent D and G bands typical of graphitic carbon. TGA further confirmed the sharp reduction in coke formation: samples with 50–75% Al₂O₃ lost <1% of their mass during deposit burnout (500–700 °C), compared to 3.9–6.4% for supports with 5–20% Al₂O₃ (Figure 5a). These findings clearly demonstrate that optimizing support composition and structure-enhancing basicity, introducing oxygen vacancies, and increasing surface area are highly effective strategies for improving EDR catalyst stability and performance.

3.2.2. Modified and Multifunctional Catalytic Systems

In addition to support optimization, considerable research has focused on the development of modified and multifunctional catalytic systems that combine the advantages of multiple components to improve activity and resistance to coking. These include bimetallic catalysts, perovskite-type oxides, high-entropy materials, core–shell structures, and metal–organic framework (MOF)-derived catalysts. Key advancements in each of these approaches are discussed below.

Bimetallic and Promoted Catalysts. The incorporation of a second metal or promoter frequently leads to reduced coke formation without compromising catalytic activity. For instance, the addition of cobalt to a Ni-based catalyst supported on CeO₂-ZrO₂ significantly reduces carbon accumulation during DRM and EDR processes, while Ni remains the primary active component. Fedorova et al. [127] demonstrated that a Ni-Co/Ce_0.75Zr_0.25O₂ bimetallic catalyst exhibited superior H₂ and CO yields at 700 °C. The presence of Co decreased the rate of coking without negatively influencing the activity of the main reforming reactions. TPR analysis showed that Co weakens the strong interaction between Ni and the oxide support, inhibiting the formation of hard-to-reduce NiO phases and thus enhancing the long-term stability of the catalytic system.

Similarly, doping Ni catalysts with copper can improve metal dispersion and reduce the tendency for carbon deposition via the formation of Cu-Ni alloys. In [128], the addition of 1 wt.% Cu to a Ni/Al-Zr-Ce-O (50ACZ) system led to the formation of fine bimetallic particles (10–30 nm), improving metal–support interaction and inhibiting Ni agglomeration. The resulting 1Cu-9Ni/50ACZ catalyst achieved high hydrogen (78%) and CO (70%) yields at 750 °C (H₂/CO ≈ 1.1). Copper also promoted the water-gas shift (WGS) reaction, increasing the relative H₂ yield, although excessive Cu loading induced side reactions from ethanol decomposition, lowering the overall activity.

Beyond transition metal promoters, the introduction of alkali elements has proven effective in increasing surface basicity. For example, potassium-modified Ni/Al₂O₃ catalysts showed significantly improved coke resistance. The Ni/K₂O-Al₂O₃ catalyst exhibited a much slower deactivation rate (activity slope −0.96 vs. −2.77 for unmodified Ni/Al₂O₃). TEM analysis revealed dense carbon nanotube bundles on Ni/Al₂O₃, whereas significantly fewer filamentous carbon structures were observed on Ni/K₂O-Al₂O₃. TGA measurements indicated that the potassium-modified sample experienced <7% mass loss from carbon deposits (500–700 °C), compared to 20% for unmodified Ni/Al₂O₃. Raman spectra showed a reduced D/G intensity ratio (ID/IG ≈ 1.0 vs. 1.5), suggesting a lower fraction of amorphous, reactive carbon. CO₂-TPD analysis confirmed an increase in weak basic sites upon K addition, correlating with the observed suppression of coke formation.

In summary, both bimetallic and alkali-promoted catalytic systems exhibit extended operational lifetimes by effectively limiting carbon deposition, thereby preserving Ni activity over prolonged reaction periods. The stability of Ni/Al₂O₃ and Ni/M₂O–Al₂O₃ (M = Li, Na, K) catalysts during the EDR process was evaluated using TEM, TGA, and Raman analyses (Figure 6).

Core–Shell structures and calcination optimization. Specifically engineered multiphase structures, such as core–shell architectures, provide a spatial separation between the reaction sites and regions prone to coke formation.

A recent study [130] demonstrated that, for a SiO₂@Co@CeO₂ core–shell catalyst, the calcination temperature plays a crucial role in determining catalytic performance. Calcination at 550 °C preserved the integrity of the shell structure and facilitated the formation of an active interfacial layer between Co and CeO₂. As a result, the catalyst achieved complete ethanol conversion at just 500 °C and exhibited excellent stability. At this optimal treatment temperature, the amount of carbon deposited was less than 1 wt.% (according to TGA data), with the carbon deposits primarily in an amorphous form, as indicated by a Raman ID/IG ratio of approximately 0.77. Figure 7 presents TEM images of the spent SiO₂@Co@CeO₂ catalysts calcined at 550 °C, 700 °C, and 850 °C after undergoing the EDR reaction, illustrating the morphological changes and structural degradation with increasing calcination temperature. Increasing the calcination temperature to 700–850 °C led to a partial loss of the core–shell configuration, as evidenced by the agglomeration of Co₃O₄ and CeO₂ nanoparticles and the formation of filamentous carbon deposits on the spent catalyst surface. The ID/IG ratio in Raman spectra decreased to the range of 0.4–0.6, indicating a higher proportion of graphitized carbon. TEM images of the spent catalysts further support these findings: in samples calcined at 550 °C and 700 °C (Figure 7a,b), the shell structure was preserved with minimal carbon deposition, while the sample calcined at 850 °C (Figure 7c) exhibited significant filamentous carbon formation along with aggregation of Co₃O₄ and CeO₂ nanoparticles. These results highlight the critical importance of optimizing the calcination temperature to enhance the structural integrity and operational stability of core–shell catalysts under EDR conditions.

Such structural degradation is associated with accelerated catalyst deactivation. Therefore, precise control of thermal treatment parameters is essential for improving catalyst longevity by ensuring the formation of favorable structural and carbon deposition characteristics.

3.2.3. Advanced Catalytic Materials

Perovskite-based oxide catalysts. Complex oxides with perovskite-like structures have attracted considerable interest due to their compositional flexibility, high redox capacity, and robustness under harsh reaction environments [131]. In particular, copper-based perovskites such as LaCuO₃ and CeCuO₃ have demonstrated promising activity in EDR. LaCuO₃ synthesized via the citrate gel method enabled complete CO₂ conversion at approximately 706 °C, whereas CeCuO₃ required a significantly higher temperature (840 °C) to achieve comparable performance.

As the reaction temperature increased from 725 °C to 800 °C, the H₂/CO ratio for LaCuO₃ decreased from 1.7 to 1.0 due to the suppression of side reactions, bringing the syngas composition closer to the stoichiometric ratio. The maximum CO yield reached 30% for LaCuO₃ at the optimal feed ratio. Post-reaction XPS analysis revealed the formation of metallic Cu⁰ and an enrichment of surface-active oxygen species, with LaCuO₃ exhibiting a higher surface oxygen content than CeCuO₃. This finding is supported by TEM data: LaCuO₃ retained its porous morphology with negligible carbon deposition, whereas CeCuO₃ showed extensive formation of filamentous and amorphous carbon structures on its surface. Recent progress has also been made in the development of high-entropy perovskite oxides (Figure 8), which represent an advanced class of catalysts for EDR due to their enhanced thermal stability and oxygen mobility.

Eremeev et al. [132] synthesized a series of five-component perovskites, La(Cr_0.2Mn_0.2Fe_0.2Co_0.2Ni_0.2)O₃ and La(Ti_0.2Mn_0.2Fe_0.2Co_0.2Ni_0.2)O₃, which were subsequently impregnated with 5 wt.% Ni. Upon reduction, these high-entropy oxide-based catalysts exhibited outstanding catalytic activity in EDR: ethanol conversion reached 95–100%, while CO₂ conversion was up to 65%, yielding a H₂/CO ratio of 1.1–1.2 at 700 °C. The best performance was observed for the La(Cr_0.2Mn_0.2Fe_0.2Co_0.2Ni_0.2)O₃-based catalyst, which is attributed to its enhanced oxygen mobility and the presence of thermally stable defect states within the lattice. Importantly, after 10 h of continuous operation, no significant growth of Ni nanoparticles or formation of graphitized carbon was observed, as confirmed by TEM and Raman spectroscopy. Oxygen isotope exchange measurements revealed a high level of anionic conductivity (D × 10⁻¹² cm²/s at 700 °C), which facilitates continuous removal of carbon species from the catalyst surface.

Therefore, perovskite and high-entropy oxide catalysts act as highly effective matrices for dispersing active metals and promoting the in situ oxidation of intermediate carbonaceous species, thereby substantially improving the long-term stability and performance of EDR systems.

MOF-derived and coordination polymer-based catalysts. Metal–organic frameworks (MOFs) have recently gained significant attention as precursors for the development of highly dispersed and porous catalytic systems. Pyrolysis of MOFs at moderate temperatures enables the formation of nanostructured metal oxide composites with uniformly distributed active sites. Tian et al. [133] synthesized a series of Co-MO_x catalysts (M = Ce, Zr, Zn) via thermal decomposition of corresponding MOF precursors at 600 °C. The highest catalytic activity was observed for Co-CeO₂, which achieved complete ethanol conversion at 550 °C. At 600 °C, this catalyst yielded approximately 52.3% H₂ and 44.3% CO (molar H₂/CO ratio = 1.18). Notably, the catalyst maintained stability over 40 h of operation. Its excellent performance is attributed to the formation of ultradispersed Co₃O₄ nanoparticles (5.8 nm) embedded within a CeO₂ matrix. Strong Co₃O₄-CeO₂ interaction was evidenced by a shift in the H₂-TPR reduction temperature (271 °C), indicating facile oxygen transfer from the support to the active metal sites. In contrast, analogous MOF-derived Co-ZrO₂ and Co-ZnO catalysts exhibited lower activity and higher coke formation, attributed to weaker interfacial interaction and lower oxygen mobility.

In another study [134], a bimetallic Co(Ni)/ZnO catalyst was synthesized from coordination polymers. The addition of Ni to the original Co/ZnO system significantly enhanced its performance: Co(Ni)/ZnO achieved complete ethanol conversion at 500 °C, whereas the monometallic Co/ZnO catalyst required 650 °C. Furthermore, the Co-Ni catalyst completely suppressed acetone formation as a side product (which reached up to 10 mol.% with Co/ZnO). Structural analyses (XRD, TEM, Raman, XPS) revealed that Ni incorporation reduced the average Co₃O₄ particle size (from ~20 to 17 nm) and increased the concentration of oxygen vacancies in the oxide matrix. This led to enhanced reducibility of oxide phases (as shown by H₂-TPR) and consequently higher catalytic stability. Both examples highlight the strong potential of MOF-derived catalysts, which combine high activity and coke resistance due to their nanocomposite architecture. It is worth noting, however, that while these catalysts show delayed coke formation, further investigation is required to fully understand their deactivation mechanisms, as direct quantification of deposited carbon is often not reported.

Photothermal catalysis as a hybrid approach. One of the most recent advances in enhancing EDR performance involves the integration of thermal and photon-driven activation, known as photothermal catalysis. In this approach, catalytic materials are irradiated with concentrated light sources (e.g., infrared lasers or solar simulators), inducing localized heating and the excitation of plasmonic or polaronic states that facilitate the reaction. Photothermal activation allows high conversion rates at lower external temperatures by directly heating active sites and potentially leveraging non-thermal effects (e.g., generation of hot charge carriers) [135]. For instance, it has been shown [136] that infrared illumination of a Ni/ZrO₂ catalyst increases ethanol conversion from 10% in the dark to 40% under irradiation, while simultaneously reducing the formation of byproducts such as acetone. This enhancement is attributed to photo-induced bond activation and accelerated oxidation of surface carbon intermediates, effectively raising the local temperature of catalytic sites without overheating the bulk reactor. Even more remarkable results have been achieved with specially engineered photoresponsive architectures. A dual-hollow microstructured NiZnO_x-M catalyst, developed by Li et al. [137], demonstrated more than a twofold increase in ethanol conversion under light irradiation at 450 °C compared to thermal operation alone. Simultaneously, coke formation was significantly suppressed: TGA showed only 11% mass loss from deposits, and the coke accumulation rate was as low as 1.1 mg/g·h. This photothermally activated catalyst remained stable for over 100 h. Thus, harnessing photon energy enables more energy-efficient EDR by reducing thermal input and coke formation. Photothermal strategies are emerging as promising enhancements to traditional thermocatalysis, offering a pathway toward more economical and stable ethanol CO₂ conversion processes. Integrated strategies in EDR catalyst design including bimetallic compositions, promoter additives, core–shell structures, perovskite-type materials, MOF-derived architectures, and photothermal systems demonstrate superior performance and durability compared to conventional Ni-based catalysts. These approaches provide improved metal dispersion, enhanced metal-support interactions, in situ generation of active oxygen species, and suppression of side reactions. Collectively, they significantly delay catalyst deactivation by mitigating coke accumulation and preserving active surface sites. Each strategy contributes to overcoming the inherent limitations of nickel systems and supports the advancement of sustainable and energy-efficient EDR technologies. Recent advances in EDR catalysts over the last five years are summarized in

Table 6. Recent advances in EDR catalysts (last 5 years).

Catalyst	Method of Preparation	Reaction Conditions	Reduction Conditions	Activity	Stability	Ref
15 wt.% Cu-Ce0.8Zr0.2O2	co-precipitation	T = 700 °C, EtOH/CO2 = 1:1; volumetric velocity = 14,000 mL/gcat/h	in situ T = 500 °C for 1 h, 5 vol.% H2/N2 (30 mL/min)	XC2H5OH = 90%, yield CO = 37%, yield H2 = 22%, yield CH4 = 28%	50 h	[125]
3wt.%La–10 wt.% Cu/Al2O3	wet impregnation	T = 750 °C, EtOH/CO2 = 1:1	n/a-	XC2H5OH = 87.6% XCO2 = 55.1% yield CO = 27% yield H2 = 52%	-	[138]
Mn-15 wt.% Co/CeO2	urea co-precipitation	T = 650 °C, EtOH/CO2/N2 = 1:1:2 volumetric velocity = 14,000 mLgcat−1 h−1).	n/a	XC2H5OH = 97% Yield H2 = 45 mol.% yield CO = 45 mol.%	50 h	[139]
LaCuO3 (bulk perovskite)	citrate sol–gel	T = 750 °C volumetric velocity = 42 L/gcat/h	n/a	XC2H5OH = 93.7% yield H2 = 54%, yield CO = 50%	-	[118]
5 wt.%Ni/Ce0.75Zr0.25- x(Nb,Ti)xO2-δ	solvothermal method	EtOH/CO2 =1:1	T = 650 °C for 1 h, 5 vol.% H2/N2 (100 mL/min)	XCO2 = 60–80%	-	[140]
8.09 wt.% CoCe-MOF	solvothermal method	EtOH/CO2/N2 = 1:1:1.5, GHSV = 27,700 mLgcat−1 h−1	in situ T = 500 °C for 1 h, 5 vol.% H2/N2 (40 mL/min)	XC2H5OH = 97%	40 h	[141]
13.7 wt.% CoZnO-HT	hard template method	T = 650 °C, EtOH/CO2/N2 = 1:1:1	T = 500 °C for 1 h, 5 vol.% H2/N2	XC2H5OH = 100%, XCO2 = 25% yield H2 = 30 mol.% yield CO = 40 mol.%	40 h	[123]
SiO2@Co@CeO2	electrostatic adsorption	T = 500 °C, EtOH/CO2/N2 = 1:1:1.5, GHSV = 27,700 mLg−1 h−1	T = 500 °C for 1 h, H2/N2 5 vol.% (40 mL/min)	XC2H5OH = 92% yield H2 = 55.1 mol.% yield CO = 17.8 mol.%	15 h	[130]
10 wt.% Ni/ACZ	sol–gel	T = 650 °C, EtOH:CO2 = 1:1.8	n/a	XC2H5OH = 100%, XCO2 = 63%	7 h	[126]
9.3 wt.% NiZnOx-M	template method	EtOH/CO2/N2 = 1:1:3	in situ T = 500 °C for 1 h, 5 vol.% H2/N2	XC2H5OH = 80%	100 h	[137]
10 wt.% Ni/35AZ	sol–gel	T = 600 °C, CO2/C2H5OH = 1.4:1	n/a	yield H2 = 47% yield = CO 34%	-	[120]
12 wt.% Ni/CoZn-MOF	MOF precursor-based method	EtOH/CO2/N2 = 1:1:1, 14,000 mLg−1 h−1	5 vol.% H2/N2 (40 mL/min)	XC2H5OH = 100% yield H2 = 47%	-	[134]
Ni/ZrO2	precipitation method	T = 450 °C, EtOH:CO2 = 1:1	n/a	XC2H5OH = 70%	40 h	[136]
5 wt.% Ni/La(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 (LCMFCN)	citrate method	T = 700 °C, EtOH/CO2 = 1:1	T = 600 °C for 1 h, 5% H2+Ar 2 vol.% EtOH + 2 vol.% CO2 + Ar, T = 600–750 °C	XC2H5OH = 99.7% yield H2 = 50% yield CO = 87%	5 h	[132]

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4. Comparative Analysis of DRM and EDR

Although both dry reforming of methane (DRM) and dry reforming of ethanol (EDR) share the overarching goal of transforming CO₂ into valuable syngas, the two processes differ in fundamental ways that strongly influence their thermodynamics, reaction mechanisms, and catalyst design strategies. DRM is governed by the activation of methane and carbon dioxide, two of the most inert molecules in chemistry. As a consequence, high operating temperatures (typically above 700 °C) are required to overcome the formidable energy barriers associated with C–H and C=O bond cleavage. These harsh conditions inevitably exacerbate catalyst deactivation, particularly through carbon deposition via methane cracking and the Boudouard reaction, as well as through thermal sintering of metallic particles. In contrast, EDR benefits from the presence of ethanol, whose C–C and C–O bonds are significantly weaker, enabling the process to proceed at milder temperatures (300–600 °C). Yet this apparent advantage comes with its own challenges: ethanol undergoes a complex network of side reactions, including dehydration to ethylene and dehydrogenation to acetaldehyde, both of which are prone to further polymerization and condensation. Such pathways lead to the formation of amorphous or polymeric carbon, which can rapidly accumulate and poison active sites even under relatively moderate conditions.

Beyond thermodynamics, the feedstock basis of DRM and EDR also underscores their complementary roles in carbon management. DRM primarily relies on natural gas or biogas as a methane source, enabling the simultaneous utilization of CH₄ and CO₂ two of the most potent greenhouse gases. This dual mitigation strategy makes DRM attractive in regions where methane-rich resources are abundant. On the other hand, EDR employs bio-ethanol, a renewable and widely available liquid fuel produced from biomass. This direct coupling of renewable carbon with CO₂ utilization situates EDR within the broader context of biorefineries and the circular carbon economy, highlighting its potential contribution to sustainable fuel and chemical production.

Catalyst development reveals important parallels between the two processes. Nickel remains the most extensively investigated active phase for both DRM and EDR, striking a practical balance between activity and cost. However, the intrinsic drawbacks of Ni, including its susceptibility to coking and sintering, necessitate careful catalyst engineering. Strategies such as the incorporation of CeO₂, ZrO₂, or other oxygen-storage materials to generate lattice oxygen, the promotion with rare-earth or alkaline elements to enhance CO₂ activation, and the design of confinement architectures (core–shell structures, mesoporous frameworks) have been shown to suppress carbon accumulation and extend catalyst lifetime. In DRM, these measures primarily address graphitic or filamentous carbon formed at high temperatures, while in EDR they combat polymeric and oxygen-rich carbon species derived from ethanol intermediates. In both cases, oxygen-vacancy engineering and strong metal-support interactions emerge as unifying design principles that underpin catalyst stability. However, the optimum characteristics of the support are not identical. In DRM, carried out at ≥700 °C, thermally robust oxides with strong metal–support interaction (e.g., ZrO₂, CeO₂–ZrO₂) are required to suppress Ni sintering and facilitate the removal of graphitic carbon. In EDR, which proceeds at 300–600 °C, excessively strong interaction is less advantageous; defect-rich but moderately interacting supports (e.g., CeO₂, Ce–La oxides) are preferable, as they provide oxygen vacancies and limit ethanol dehydration while maintaining accessible Ni sites. This distinction highlights that MSI must be tuned to the reaction environment rather than applied as a universal rule. From a process-engineering standpoint, DRM remains thermally demanding, raising questions of heat management, reactor materials, and long-term catalyst integrity. EDR, while more moderate in terms of thermal input, requires stringent control over selectivity to avoid the build-up of undesired by-products. Both processes typically yield syngas with an H₂/CO ratio close to unity well suited for Fischer-Tropsch synthesis and methanol production, yet in DRM this ratio often requires further adjustment, while in EDR it can be tuned more flexibly through co-feeding of oxygen or steam.

Modern synthesis routes for DRM and EDR catalysts. Recent progress in catalyst synthesis for dry reforming of methane (DRM) and ethanol dry reforming (EDR) centers on confinement architectures, defect/oxygen-mobility engineering, and thin-film or exsolution routes tailored to suppress coking and sintering while preserving metal dispersion.

For DRM, core–shell confinement has proved especially effective: Ni nanoparticles anchored as phyllosilicates and encapsulated by a porous SiO₂ shell (∼20 nm) limit carbon growth and particle migration; a representative Ni/SiO₂@SiO₂ system prepared via ammonia-evaporation anchoring followed by sol–gel shelling remains stable at 600 °C [142]. In parallel, physical vapor deposition (PVD) enables ultrathin, adherent Ni layers on microchannel supports (Al₂O₃–ZrO₂), combining short diffusion lengths with excellent coke resistance under DRM; magnetron-sputtered films demonstrate stable time-on-stream behavior [143]. MOF/mesotemplate routes continue to deliver high dispersion and fast mass transfer (e.g., CeO₂-, ZrO₂- or SiO₂-based mesostructures), leveraging oxygen-vacancy formation to gasify CH_x intermediates and suppress graphitic carbon. For EDR, high-entropy perovskite (HEO) precursors synthesized by modified Pechini/citrate methods and then Ni-impregnated yield defect-rich lattices with moderate high oxygen mobility and socketed Ni after reduction, offering high conversion with limited carbon deposition at 700 °C [132]. These HEOs align with the broader exsolution strategy whereby reducible perovskites nucleate strongly anchored nanoparticles under activation.

Nanocasting and MOF-derived approaches also feature prominently in EDR: Ni/KIT-6 and co-nanocast Ni/Ce_0.8Zr_0.2O₂ frameworks enhance dispersion and stability while tuning acid–base sites to suppress ethanol dehydration [119,122]. Finally, infiltration of active phases into porous backbones (e.g., fuel-cell style electrodes) provides high triple-phase boundary density and robust metal anchoring for EDR operation [111].

In DRM, thin-film/confinement routes (core–shell or PVD) paired with vacancy-rich supports are now the most reliable path to coke tolerance above 700 °C. In EDR, HEO/perovskite-derived scaffolds with controlled exsolution, complemented by nanocasting to regulate acid–base chemistry, offer the best stability–selectivity balance at 300–600 °C. Prioritizing socketed metal states and oxygen-transport pathways should be the design default across both chemistries.

Taken together, DRM and EDR should not be viewed as competing but rather as complementary routes in the portfolio of CO₂ utilization technologies. DRM is ideally positioned where methane resources and CO₂ emissions intersect, while EDR aligns more naturally with renewable ethanol platforms and biorefinery schemes. Importantly, advances in catalyst design whether through defect engineering, perovskite or MOF-derived structures, or high-entropy alloys tend to be transferable across both systems, suggesting that progress in one domain accelerates development in the other. Ultimately, the integration of DRM and EDR within future energy and chemical production pathways will depend not only on catalyst innovation but also on their alignment with regional feedstock availability and decarbonization strategies. The advantages and disadvantages of DRM and EDR are compared in

Table 7. Advantages and disadvantages of DRM and EDR.

Process	Advantages	Disadvantages
DRM	Utilizes two greenhouse gases simultaneously (CH4 and CO2); Produces syngas with H2/CO ≈ 1 (suitable for Fischer–Tropsch and oxygenate synthesis); Well-studied with extensive literature and pilot trials	Requires very high temperatures (≥700 °C); Severe coking via CH4 cracking and Boudouard reaction; Ni sintering at elevated temperatures; H2/CO ratio often needs adjustment for downstream use
EDR	Combines renewable ethanol with CO2 utilization (bio-based, sustainable); Operates at milder temperatures (300–600 °C); Produces syngas with H2/CO ≈ 1, closer to downstream optimum; Attractive integration into biorefinery concepts	Complex reaction network (dehydration, dehydrogenation, condensation); Formation of oxygenates and polymeric coke precursors; Catalyst deactivation through coke and side-products; Still an emerging technology with limited pilot-scale validation

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5. Conclusions and Future Perspectives

Catalytic dry reforming of methane and ethanol represents a promising technological pathway for simultaneously addressing environmental challenges and producing valuable chemical products. These processes play a critical role in mitigating climate change while fostering the transition toward more sustainable and environmentally responsible technologies in the energy and chemical sectors.

Rational catalyst design remains central to optimizing reforming reactions. Careful selection of active metal components, support materials, and promoters is essential for achieving high catalytic activity, long-term stability, and resistance to carbon deposition.

This review demonstrates that suppression of coking and improvement in catalyst stability can be achieved through a combination of specific strategies, including the creation of oxygen vacancies in supports (CeO₂, ZrO₂), doping with rare-earth (La, Ce, Pr) and transition metals, spatial confinement of active particles within mesoporous structures, and morphological control through core–shell architectures. Notably, similar stabilization strategies applied to Ni-, Cu-, and Co-based as well as perovskite-type systems enhance their resilience in both DRM and EDR, despite differences in feedstocks and coping mechanisms.

Future progress should focus on several key directions: optimization of catalyst synthesis for improved control of morphology, porosity, and metal dispersion; investigation of the in situ dynamics of active sites using advanced characterization methods (e.g., EXAFS, DFT modeling); development of hybrid catalysts that integrate the advantages of different systems; integration with renewable energy sources to reduce the carbon footprint; and scaling up laboratory technologies for industrial applications. The implementation of these approaches will enable the development of next-generation catalysts capable of meeting modern requirements for environmental compatibility, energy efficiency, and economic viability in the conversion of greenhouse gases into valuable chemical products.