CO2 methanation is promising both for using captured carbon dioxide and storing renewable energy. Ni supported on magnesium oxide is known to be an efficient catalyst for this reaction. Here, we have investigated the use of CO2 to prepare mixed magnesium and nickel carbonates which were thermally converted into mixed nickel and magnesium oxides with 4.2 to 12.8 Ni wt.%. After reduction at 900 degrees C, Ni-0-MgO sample containing 8.5 wt.% Ni displayed the highest activity (70% conversion and 98% methane selectivity) at 350 degrees C and 9,000 mL/h.gcat. Such catalyst was stable for more than 20 h. Nitrogen adsorption/desorption, XRD, TEM, TPR and TPD techniques were used to analyze the structural and physicochemical properties of the materials before reduction, after reduction and after methanation. Detailed characterizations revealed that the superior performance of the Ni-0-MgO catalyst with 8.5 wt.% Ni originated from its better textural properties, the relatively smaller Ni nanoparticle size as well as high proportion of low- and medium-strength basic sites. In this work, it appeared that methanation induced the decrease of Ni nanoparticles size as the result of Ni atoms redistribution for Ni-MgO solids with Ni wt.% lower than 10%.

CO2 methanation has been considered as a promising method for carbon capture and utilization (CCU), and the lowering of the reaction temperature has become a key focus in current research. Herein, Ni-based catalysts supported on molecular sieves (beta, HZSM-5, NaY, and Y) are prepared, and techniques including BET, XRD, H2-TPR, CO2-TPD, NH3-TPD, and XPS are employed to characterize them. Ni/beta(Si/Al similar to 12.5) reached 71.1% CO2 conversion and 97.2% CH4 selectivity at 325 degrees C, much lower than the corresponding temperature on other catalysts, which may be attributed to the moderate metal-support interactions and medium Ni particles tuned by the support. In situ DRIFTS indicated that formate and CO pathways coexisted during the reaction process over Ni/beta(Si/Al similar to 12.5), and the CO route with linear and bridge CO* as intermediates was predominant above 325 degrees C, increasing both CO2 conversion and CH4 selectivity. These findings may offer valuable insights into support selection and a mechanistic understanding.

Metal-oxide interfaces are critical for catalytic activity and stability. This work demonstrated that the incorporation of gadolinium (Gd) as a promoter in inverse ZrO2/Ni catalyst significantly enhanced its CO2 methanation performance, with 5Gd65ZrO2/30Ni demonstrating the highest catalytic activity. Characterization results indicated that Gd increased the surface area, promoted metal-support interaction, increased the concentration of oxygen vacancies, and generated a greater number of reactive ZrO2-Ni interfaces. In-situ DRIFT experiments to investigate the reaction mechanism revealed that the reaction path of CO2 methanation over inverse ZrO2/Ni catalysts was formate route, and the addition of Gd facilitated the formation of key reaction intermediates, thus accelerating the overall CO2 methanation process. These findings provide valuable insights for the design of highly active and efficient CO2 methanation catalysts.

CO2 methanation reaction is a promising approach for both CO2 utilization and hydrogen storage, leveraging hydrogen produced from renewable energy sources to mitigate the energy crisis. Inverse ZrO2/Ni catalysts promoted with Y, La, Sr, and Pr were synthesized and evaluated for CO2 methanation. The impact of these promoters on the structure, properties, and catalytic performance of inverse ZrO2/Ni catalyst was systematically investigated. A comprehensive suite of characterization techniques, including XRD, BET, H2-TPR, CO2-TPD, TEM, HRTEM, EDX-Mapping, and quasi in-situ XPS, was employed to elucidate the relationship between the physicochemical properties of the catalysts and their CO2 methanation catalytic performance. 5Y65Zr/30Ni catalyst exhibited superior methanation activity compared with other catalysts, which was correlated with its enhanced specific surface area, a high concentration of medium basic sites facilitating CO2 adsorption and activation, a high surface oxygen ratio, and optimal Ni dispersion achieved through minimized Ni crystallite size. These findings demonstrated that the strategic incorporation of promoters allowed for precise tailoring of inverse ZrO2/Ni catalyst properties, providing valuable insights for the rational design of highly efficient CO2 methanation catalysts.

The macroporous 3D architecture of the open-cell foams enables superior heat and mass transfer, exceptional thermal conductivity, rapid heat dissipation, and minimal diffusion resistance, ensuring structural stability under the highly exothermic methanation conditions. Herein, this work investigates and compares the performance of ZrO2-based 3D structured foams for thermocatalytic conversion of CO2 to methane with excellent selectivity. The foams were coated using the solution combustion method, where initially 40 wt% Ce and (5-15 wt%) Mg were coated, and a further 30 wt% nickel was utilized for coating. The catalyst was characterized via PXRD, SEM, H2-TPR, and CO2-TPD, and FE-SEM, EDX analysis confirmed the presence of Ce, Mg, Ni, and O. The catalyst showed 78% conversion with similar to 99% selectivity at 300 degrees C, whereas foams without using Mg promoter showed only 17% conversion with 90% selectivity towards methane. This result confirmed the synergistic effect between the Ce-Mg for the CO2 methanation reaction and can be linked with the basicity of the Ni/Ce-Mg catalyst. Overall, this work contributes to CO2 valorization and methane production with excellent selectivity and an easy synthesis process.

We report the synthesis of a high-performance CO2 methanation catalyst, Ni-Y1/CeO2, comprising Ni nanoparticles and atomically dispersed Y3 + on a ceria support. This precisely designed catalyst achieved an outstanding CO2 conversion of 83 % with 100 % CH4 selectivity at 350 degrees C. XAS unambiguously confirmed the atomic dispersion of Y3+ with the absence of any Y-Y bonds, while STEM-EDS revealed uniform Y distribution with finely dispersed Ni NPs. Enhanced oxygen vacancies and improved basic sites contributed to the superior activity of Ni-Y1/CeO2 even at low temperature (250-300 degrees C) and showed excellent stability over 40 h. Comparative studies with impregnated NiY/CeO2-imp and Ni/CeO2 highlighted the synergistic effect of Y3+ and Ni. These results establish Y3+ single-atom modulation as a powerful approach to tailoring basic sites and enhanced oxygen vacancies, unlocking new design pathways for advanced CO2 methanation catalysts.

A series of mixed-oxide Ni-Mg-Al CO2 hydrogenation catalysts was prepared with microwave assisted solution combustion synthesis. The physicochemical properties were influenced by the amount of urea delivered for the combustion, altering the texture and pore development. Lower microwave powers improve the surface basicity. Most significant, however, is the oxygen-deficient periclase phase, which promoted the partial formation of NiAl2O4 under reduction conditions and is proposed to indirectly enhance catalytic performance through improved surface structural reactivity. Two microwave-derived samples were compared with their counterparts obtained via thermal solution combustion synthesis and thermally decomposed hydrotalcites and examined under operando conditions with XRD-XAS. The results confirmed that incomplete reduction of nickel, followed with formation of NiAl2O4 phase delivers the most catalytically active materials. Spinel was found to improve textural properties and led to a formation of new strong surface basic sites able to interact strongly with CO2 and weakly with CO.

CO2 methanation offers the dual benefits of emission mitigation and energy storage. MgO is considered an ideal support for this process due to its high alkalinity and excellent CO2 adsorption capacity. In this study, a series of Ni-MgO materials (c.a. 10 wt% Ni) supported on high-surface-area MgO (up to 100 m2/g) derived from the thermal treatment of Upsalite (R) were synthesized using various methods (wet impregnation (WET), incipient wetness impregnation (IWI), and one-pot (OP)) and evaluated for CO2 methanation. Among them, the catalyst prepared via wet impregnation of mesoporous magnesium carbonate exhibited the highest activity, achieving 86 % CO2 conversion and 100 % selectivity towards methane at 350 degrees C. In all cases, the size of the Ni nanoparticles did not increase during the methanation test, even for the longest exposition times, as a result of strong metal-support interactions (SMSI) between Ni and MgO. Ni atom redistribution could be emphasized for Ni-MgO prepared by the IWI and OP methods, leading to smaller particles after the test, but in the end, the best catalyst (WET) was not the one with the smallest Ni nanoparticles but the one showing very constant nanoparticle size throughout methanation. The WET sample was also characterized by the highest percentage of reduced Ni, the highest number of basic sites (CO2 TPD), and the lowest surface oxygen species (XPS). Furthermore, in situ DRIFTS analyses confirmed that CO2 methanation over Ni/MgO proceeds via the formate pathway, with HCOO* identified as the key intermediate. These results underscore the synergistic effect of Ni nanoparticles and MgO support and provide valuable insights for the rational design of highly efficient Ni-based catalysts for CO2 methanation.

This study explores the catalytic performance of solution combustion-synthesized doped defective fluorite catalysts, La2-xSrxCe2-yNiyO7, for the dry reforming of methane. A comprehensive structural analysis, supported by theoretical calculations, revealed that the adopted synthetic methodology enabled Ni doping beyond a critical concentration, leading to its occupation of the interstitial lattice sites. The optimally doped Ni-containing defective fluorite oxide La1.9Sr0.1Ce1.7Ni0.3O7 exhibited superior catalytic activity with more than 70% conversion of CO2 and CH4 with an H2/CO ratio of 0.7 for a 50-h reaction at 700 °C. The prolonged reforming reaction also resulted in minimal coke deposition (11 μgc gcat-1 h-1), primarily due to the oxidative dissociation pathway of methane, as revealed through mechanistic analysis. Detailed surface studies highlighted the crucial role of metal-support interactions, wherein facile electron transfer from Ni to Ce during the reaction contributed significantly to the enhanced catalytic performance. Thus, this study establishes a strategic framework for designing and developing defect-engineered oxide catalysts, paving the way for advanced materials in dry methane reforming.

Developing an environmentally friendly and highly efficient catalyst is crucial for generating clean hydrogen without COx and structured carbon. The catalytic decomposition of methane encourages technology to convert natural gas into these valuable products. For this purpose, surface defects in activating CH4 have garnered much interest in developing silica-supported nickel catalysts by maintaining active sites and modulating metal-support interaction (MSI). Thus, It is shown here that the presence of Mn improved the reducibility of superficial NiO and created a moderate interaction between Ni and the support, decreasing the electron density around the Ni atom and elevating surface oxygen species’ presence by introducing lattice defects, thus facilitating the reduction, promoting the dissociation of methane on the nickel surface and enhancing the reactivity of the reaction Consequently, this MSI modulate stabilized the active sites, preventing quick sintering under reaction conditions. Based on TEM analysis, the surface morphology revealed well-dispersed metallic Ni and the restriction of Ni crystal growth. The strong metal-support interaction resulted in a high carbon diffusion driving force, providing more sites for growth in carbon nanofiber (CNFs). Maintaining the balance between the infiltration of dissolved carbon and the expansion of CNFs while also preventing the deactivation of the catalyst due to the covering of active sites by channeling carbon deposits towards the edges of the active sites and oxidation of coke produced by active oxygen species, all showed the effective presence of manganese in the catalyst’s configuration.

Although catalytic CO2 methanation presents a viable strategy for addressing global CO2 concerns, conventional routes are constrained by high operating temperatures, and plasma applications are non-selective toward methane. Consequently, developing a suitable catalyst remains a significant question. Hydrotalcite-induced mixed oxide (HiMO) catalyst is a promising candidate for cost-effectiveness but faces challenges with thermal stability and surface area. This work introduces a novel synthesis method by integrating Polymer P123 and transitional metals (Mn, Fe, Co, Cu), simplifying the synthesis in one step, followed by vigorous catalyst characterizations. The Ni15Fe1(Mg,Al)Ox@3P123 catalyst demonstrates a CO2 conversion of 90.5 % and CH4 selectivity of 99.7 % at 300 degrees C, alongside 85.5 % conversion and near-100 % selectivity at 33.4 W (160 degrees C) under DBD-plasma conditions, outpacing data reported in the literature. This synthesis approach can be adapted for various catalytic CO2 applications. Besides, the roles of the incorporated metals are systematically delineated. Further Operando-FTIR experiments reveal critical insights into the different pathways between thermal and plasma conditions. Critically, the correlations between the catalysts' physicochemical properties (e.g., Ni0 particle size, basicity), electrical characteristics (e.g., dielectric constant), and plasma parameters with catalytic performance at atmospheric pressure over HiMO are drawn for the first time.

The accurate generation of pore networks is essential for simulating diffusion and reaction processes within catalytic pellets. Traditional methods, which rely on Cartesian coordinates, are not well aligned with the inherent symmetry and geometry of spherical particles. This study introduces an innovative approach for constructing pore networks within spherical domains by utilizing a spherical coordinate system. A stochastic network generation algorithm was employed to preserve realistic porosity and pore connectivity. The generated networks were then used to simulate diffusion and catalytic reactions, with a particular focus on the hydrogenation of benzene as a case study. The model was validated for a wide range of porosities (0.35-0.7) and average network connectivity (4-8). The effect of node density on pore size and porosity was investigated, showing that increasing the number of nodes from 3000 to 10,000 leads to a denser and more interconnected network, requiring a reduction in mean pore radius to maintain the target porosity. Furthermore, the impact of particle size on the effectiveness factor (eta) was examined and compared to the results of the classical continuum model, where a deviation of less than 5% was observed between the two approaches. The concentration profile showed greater variation along the radial direction, leading to a significant reduction in eta at lower porosities. It was observed that for smaller particles (radii <= 1 mm), eta remains close to unity. In contrast, in particles with radii larger than 4 mm, the radial concentration gradients intensified, leading to a noticeable decrease in eta. These findings highlight the strong interplay between geometry, diffusion limitations, and reaction kinetics, providing a valuable framework for optimizing catalyst design.

In this study, uniformly dispersed Pr3+ as an isolated atom over Ni/CeO2 catalyst (Ni-Pr/CeO2) is designed to enhance catalytic activity for CO2 methanation, achieving an impressive 87% conversion with approximate to 100% CH4 selectivity at 300 degrees C temperature. In contrast, the traditional Ni/CeO2 and NiPr/CeO2-imp catalysts exhibit poor conversion and selectivity, highlighting the proof of concept on the advantage of atomic-scale dispersion. Structural analysis via PXRD, XAS, and XPS confirms the successful incorporation of Pr3+ into the CeO2 lattice by creating defects. XPS and XAS studies further reveal a significant increase in oxygen vacancies, a key factor in enhancing catalytic performance at lower reaction temperatures. STEM-EDS analysis confirms the ultra-dispersion of Pr3+ (approximate to 7 wt.%) over CeO2, ensuring a highly active catalyst surface. H-2-TPR and CO2-TPD results suggest that the Pr3+ doping enhances the catalytic activity by decreasing the reduction temperature and increasing basic sites. Additionally, long-term stability tests demonstrate no significant loss in activity over 40 h, confirming the catalyst's robustness and recyclability. This work provides critical insights into the structure-activity relationship of Pr3+-modified Ni/CeO2 catalysts, emphasizing the role of oxygen vacancies in optimizing CO2 hydrogenation efficiency.

A series of nanostructured Ni/SBA-16 catalysts doped with different Ti loadings (0-10 wt%) were prepared and their catalytic behaviors were investigated in the CO2 reforming of methane reaction. Comprehensive physicochemical analyses revealed that a 2 wt% Ti -doping markedly lowered Ni particle size, enlarged specific surface area and mesopore volume, facilitated NiO reduction, intensified metal-support interaction, and enriched surface-active oxygen species, leading to optimal catalytic activity and coke resistance. However, higher Ti loadings (5-10 %) caused degradation of these structural properties compared to the optimal 2 wt% Ti loading, primarily due to the formation of NiTiO3 oxides. Consequently, catalytic performance was significantly reduced. Based on these findings, a synergistic relationship between the active metal (Ni) and tailored surface characteristics was established, which was correlated with the enhanced catalytic activity in the CO2 reforming of methane reaction.

The catalytic conversion of carbon dioxide to useful products such as methane is one of the best alternatives to address the growing energy demand resulting from the depletion of fossil fuels. In this work, Co3O4 and Ni substituted Co3O4 catalysts were synthesized by a single-step solution combustion method and their ability for CO2 hydrogenation to form methane were evaluated. Ni substitution improved the methanation activity with successful substitution achieved up to 15 at% within Co3O4 lattice. Ni substitution resulted more oxygen vacancies. Subsequent reduction treatment further enhanced the oxygen vacancy concentration and facilitated CO2 activation. The physical, structural, morphological, elemental and redox properties of the catalysts were characterized by XRD, XPS, SEM, TEM, N-2 adsorption-desorption, ICP-OES, H-2-TPR, CO2-TPD, CO2-TPD-MS and H-2 pulse titration techniques. All Ni-doped catalysts offered decent performance. However, the fresh 20%Ni substituted Co3O4 catalyst demonstrated the highest performance, achieving 58% CO2 conversion and 90% CH4 selectivity at 400 degrees C. The catalyst showed significantly enhanced performance following the creation of vacancies through reduction. The CO2 conversion increased to 78% with >98% CH4 selectivity at 400 degrees C. The apparent activation energy of the reduced 20%Ni/Co3O4 was determined to be the lowest at 21.6 +/- 0.6 kJ. mol(-1). Mechanistic insights and the role of oxygen vacancies were further investigated through DFT and in situ FTIR studies. A combined formate and CO pathway was identified as the reaction mechanism over 20%Ni/Co3O4.

This study explores the catalytic performance of solution combustion-synthesized doped defective fluorite catalysts, La2-xSrxCe2-yNiyO7, for the dry reforming of methane. A comprehensive structural analysis, supported by theoretical calculations, revealed that the adopted synthetic methodology enabled Ni doping beyond a critical concentration, leading to its occupation of the interstitial lattice sites. The optimally doped Ni-containing defective fluorite oxide La1.9Sr0.1Ce1.7Ni0.3O7 exhibited superior catalytic activity with more than 70% conversion of CO2 and CH4 with an H-2/CO ratio of 0.7 for a 50-h reaction at 700 degrees C. The prolonged reforming reaction also resulted in minimal coke deposition (11 mu g(c) g(cat)(-1) h(-1)), primarily due to the oxidative dissociation pathway of methane, as revealed through mechanistic analysis. Detailed surface studies highlighted the crucial role of metal-support interactions, wherein facile electron transfer from Ni to Ce during the reaction contributed significantly to the enhanced catalytic performance. Thus, this study establishes a strategic framework for designing and developing defect-engineered oxide catalysts, paving the way for advanced materials in dry methane reforming.

The catalytic hydrodeoxygenation (HDO) of lignocellulose-derived pyrolysis oil is a critical process for producing high-quality biofuels. This study investigates the effect of the Mg/Al molar ratio on the catalytic performance of CuMg(Al)O mixed oxide catalysts in the HDO reaction of benzyl alcohol as a model oxygenated compound. They were synthesized by coprecipitation with a fixed Cu content of 15 at. %, with respect to cations, and different Mg/Al molar ratios (0/1, 1/1, 3/1, 5/1, and 1/0). The catalysts were characterized using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), UV-vis spectroscopy, nitrogen adsorption-desorption isotherms, temperature-programmed reduction with hydrogen (H2-TPR), and temperature-programmed desorption (TPD) of CO2 and NH3. It has been shown that the Mg/Al molar ratio strongly influences the physicochemical characteristics of the CuMg(Al)O mixed oxides and, hence, their catalytic performance. Catalytic tests were conducted in a stainless-steel autoclave reactor and the obtained results indicated that the systems with Mg/Al molar ratios of 3/1 and 5/1, issued from layered double hydroxide precursors, exhibited the highest activity, with yields to toluene higher than 85%. This superior performance is attributed to the well-dispersed copper species on the catalyst surface combined with appropriate acid-base properties. As the CuMg(Al)O system with Mg/Al molar ratio of 5/1 was the best in terms of benzyl alcohol conversion, i.e., ca. 98% at 230 degrees C, under 5 atm of H2, for 3 h of reaction time, with high selectivity to toluene of ca. 87%, the influence of the reaction time, temperature and reusability over multiple reaction cycles on its performance were investigated.

In the presented work, the catalytic performance of a nickel catalyst, in CO2 hydrogenation to methane, within a ZrO2 open-cell foam (OCF)-based catalyst was studied. Two series of analogous samples were prepared and coated with 100–150 mg of a Mg-Al oxide interface to stabilize the formation of well-dispersed Ni crystallites, with 10–15 wt% of nickel as an active phase, based on 30 ppi foam or 45 ppi foam. The main factor influencing catalytic performance was the geometric parameters of the applied foams. The series of catalysts based on 30 ppi OCF showed CO2 conversion in the range of 30–50% at 300 °C, while those based on 45 ppi OCF resulted in a significantly enhancement of the catalytic activity: 90–92% CO2 conversion under the same experimental conditions. Calculations of the internal and external mass transfer limitations were performed. The observed difference in the catalytic activity was primarily related to the radial transport inside the pores, confirmed with the explicitly higher conversions.