Methanation Catalysts Research Articles

Local coordination environment triggers key Ni-O-Si copolymerization on silicalite-2 for dry reforming of methane

The development of dry reforming of methane (DRM) catalysts with good Ni loading, while retaining high metal dispersion is a critical issue, given the harsh industrial-relevant conditions. Here, we demonstrate the impact of the local coordination environment on the DRM activity of Ni-silicalite-2 (Ni-S2) catalysts. The grafted Ni(II) intermediates with high Ni-O-Si copolymerization (coordination number ratio Si: Ni=2.28) are discovered to redisperse Ni sites, even at 10 wt% Ni loading. Then, the partial S2 recrystallizes into new SiO2-nanowires to anchor Ni nanoparticles, via an ethylenediamine-assisted dissolution-recrystallization (enDR). Compared to the typical Ni-S2 catalyst with Ni phyllosilicate (CN ratio Si: Ni＜1), the Ni-S2-enDR shows high dispersion and stability at 800 °C and 450 L gcat−1 h−1, exhibiting negligible coke deposition and no growth of 4.25 nm Ni nanoparticles. The atomic level insights in nickel and silicon coordination reported in this work provide an instructive way of designing stable DRM catalysts.

Surface control of Ni-Al2O3 dry reforming of methane catalyst by composition segregation

Catalyst surface control is of great importance considering that a catalytic reaction initially starts with surface atoms’ interaction with reactant molecules. In the present study, we synthesized the Ni-Al2O3 dry reforming of methane (DRM) catalyst via the spray-pyrolysis-assisted evaporation-induced self-assembly (EISA) method in order to systematically investigate catalyst surface change as controlled by composition segregation. The present results showed that segregation in the Ni-Al2O3 catalyst had successfully occurred by the post-annealing process and that the segregated Ni nanoparticles were located on the catalyst surface with simultaneous reduction to metal. The size of the surface Ni nanoparticles was highly dependent on the post-annealing temperature, whereas the electronic properties did not consistently align with the trend of particle-size growth, indicating that the particle-growth mechanism underwent alterations from segregation to sintering as the temperature was increased. In other words, when the reduction temperature for metal segregation is excessively high, particle-growth on the external catalyst surface, as induced by post-annealing, is primarily attributable to particle sintering rather than to metal segregation. This phenomenon directly results in decreased Ni surface density. The catalytic DRM reaction revealed that due to sintering, the catalytic performance did not align with the trend of Ni particle-size growth, and the conversion of CH4/CO2 was closely associated with Ni surface density. This information will offer valuable insight to future research focused on development of Ni-based catalysts for DRM reactions.

Facile Synthesis Method of Zeolite NaY and Zeolite NaY-Supported Ni Catalyst with High Catalytic Activity for the Conversion of CO2 to CH4

In this work, the facile reflux method was used as a crystallization procedure for zeolite NaY synthesis. The zeolite mixture was aged for 7 days and then refluxed for crystallization at 100 °C for 12 h. The synthesized zeolite NaY was impregnated with 10, 20 and 30 wt%Ni solution to use as a catalyst for CO2 methanation. The 30 wt% of Ni on the zeolite NaY catalyst showed the highest CO2 methanation catalytic activity, with almost 100% CH4 selectivity. This can be explained by an appropriate H2 and CO2 adsorption amount on a catalyst surface being able to facilitate the surface reaction between them and further react to form products. The oxidation state of Ni and the stability of the catalyst were monitored by time-resolved X-ray absorption spectroscopy. The oxidation state of Ni2+ was reduced during the catalyst reduction prior to the CO2 methanation and it was completely reduced to Ni° at 600 °C. During CO2 methanation, Ni° remained unchanged. In addition, the stability test of the catalyst was conducted by exposing the catalyst to a fluctuating condition (CO2 + H2 and only CO2). The oxidation state of Ni° remained unchanged under the fluctuating condition. This indicated that the Ni/zeolite catalyst has high stability, which can be attributed to an appropriate binding strength between Ni and the zeolite support.

Superexchange-stabilized long-distance Cu sites in rock-salt-ordered double perovskite oxides for CO2 electromethanation

Cu-oxide-based catalysts are promising for CO2 electroreduction (CO2RR) to CH4, but suffer from inevitable reduction (to metallic Cu) and uncontrollable structural collapse. Here we report Cu-based rock-salt-ordered double perovskite oxides with superexchange-stabilized long-distance Cu sites for efficient and stable CO2-to-CH4 conversion. For the proof-of-concept catalyst of Sr2CuWO6, its corner-linked CuO6 and WO6 octahedral motifs alternate in all three crystallographic dimensions, creating sufficiently long Cu-Cu distances (at least 5.4 Å) and introducing marked superexchange interaction mainly manifested by O-anion-mediated electron transfer (from Cu to W sites). In CO2RR, the Sr2CuWO6 exhibits significant improvements (up to 14.1 folds) in activity and selectivity for CH4, together with well boosted stability, relative to a physical-mixture counterpart of CuO/WO3. Moreover, the Sr2CuWO6 is the most effective Cu-based-perovskite catalyst for CO2 methanation, achieving a remarkable selectivity of 73.1% at 400 mA cm−2 for CH4. Our experiments and theoretical calculations highlight the long Cu-Cu distances promoting *CO hydrogenation and the superexchange interaction stabilizing Cu sites as responsible for the superb performance.

Carbon Dioxide Methanation Enabled by Biochar-Nanocatalyst Composite Materials: A Mini-Review

Due to ever-increasing global warming, the scientific community is concerned with finding immediate solutions to reduce or utilize carbon dioxide (CO2) and convert it in useful compounds. In this context, the reductive process of CO2 methanation has been well-investigated and found to be attractive due to its simplicity. However, it requires the development of highly active catalysts. In this mini-review, the focus is on biochar-immobilized nanocatalysts for CO2 methanation. We summarize the recent literature on the topic, reporting strategies for designing biochar with immobilized nanocatalysts and their performance in CO2 methanation. We review the thermochemical transformation of biomass into biochar and its decoration with CO2 methanation catalysts. We also tackle direct methods of obtaining biochar nanocatalysts, in one pot, from nanocatalyst precursor-impregnated biomass. We review the effect of the initial biomass nature, as well as the conditions that permit tuning the performances of the composite catalysts. Finally, we discuss the CO2 methanation performance and how it could be improved, keeping in mind low operation costs and sustainability.

Exploring dolomite as a promising support for Ni catalysts in CO2 methanation

Ni catalysts supported on Al-modified calcined dolomite were developed, using a natural mineral as the precursor. Treatment with 3% w/w Al improved thermal stability and increased the surface area. The variation in Ni loading (5–30% w/w) was studied to characterize the structural, morphological, and chemical properties. The CO2 capture capacity of the solids, evaluated by Thermogravimetric Analysis at 400 °C (100–800 μmol∙g−1), decreased with increasing Ni loading due to the reduction of basic sites. CO2-TPD analyses revealed the presence of captured CO2 in various basic sites, especially in the strong ones, with efficient formation of thermally stable carbonates. In catalytic tests at 400 °C, conversions exceeding 50% were achieved for higher Ni loadings and around 50% for lower loadings, with 100% selectivity towards CH4. The application of in situ and operando Diffuse reflectance infrared Fourier transform spectroscopy techniques provided insights into the formation of carbonates and their transformation into formate, methoxy, and formyl species, explaining the total selectivity towards CH4 and the absence of CO in the products. This comprehensive approach significantly contributes to the understanding of the reaction dynamics and opens new perspectives for the utilization of Ni catalysts supported on modified dolomite.

The carbon deposition process on NiFe catalyst in CO methanation: A combined DFT and KMC study

Carbon deposition often occurs in CO methanation on NiFe catalyst, resulting in the deactivation of the catalyst, which is an urgent problem to be solved in industrial production. In this work, the carbon deposition process on the surface of NiFe catalyst was systematically investigated by the combination of Density Functional Theory (DFT) and Kinetic Monte Carlo (KMC). The results of DFT calculations show that for C1 ∼ C9, the most stable adsorption configurations are carbon chains while for C10 and C11, the carbon rings are the most stable. Besides, in the reaction network of carbon deposition, the formation of C2 is the key reaction with high activation energy. KMC simulation shows that temperature can significantly affect the occurrence of carbon deposition and C2 will accumulate and react to form larger carbon species instead of decomposing. In addition, the growth rate of carbon chains is faster than that of carbon rings, and carbon species mainly react with C1 and C2 to form longer carbon chains. Therefore, the anti-carbon deposition performance of the catalyst can be improved by increasing the activation energy of carbon–carbon coupling and inhibiting the formation of C2.

Mechanistic and Compositional Aspects of Industrial Catalysts for Selective CO2 Hydrogenation Processes

The characteristics of industrial catalysts for conventional water-gas shifts, methanol syntheses, methanation, and Fischer-Tropsch syntheses starting from syngases are reviewed and discussed. The information about catalysts under industrial development for the hydrogenation of captured CO2 is also reported and considered. In particular, the development of catalysts for reverse water-gas shifts, CO2 to methanol, CO2-methanation, and CO2-Fischer-Tropsch is analyzed. The difference between conventional catalysts and those needed for pure CO2 conversion is discussed. The surface chemistry of metals, oxides, and carbides involved in this field, in relation to the adsorption of hydrogen, CO, and CO2, is also briefly reviewed and critically discussed. The mechanistic aspects of the involved reactions and details on catalysts’ composition and structure are critically considered and analyzed.

High-capacity CO/CO2 methanation reactor design strategy based on 1D PFR modelling and experimental investigation

An in-depth analysis of oil-cooled and naturally ambient air-cooled fixed bed reactors for catalytic methanation of a feedgas containing CO and CO2 has been performed. Combined investigation of modelling and experiments showed, that small tube-to-pellet diameters ratios and optimized reactor cooling are beneficial for high-capacity CO/CO2 methanation. Very good model accuracy was proven with a 1D approach for small diameter reactor pipes. It is shown that the reactor design sweet spot under consideration of input gas capacity, methane output concentration, catalyst degradation and pressure loss can be assessed by the experimentally validated reactor model. The study reveals insights to the mechanism of combined CO and CO2 methanation showing that initial CO methanation is kinetically limited, while subsequent CO2 methanation is ruled by the kinetics of the reverse water gas shift reaction. Finally, this works aim is to provide a design strategy for effective and cheap high-capacity CO/CO2 methanation reactors for industrial scale using commercial pellet catalysts in oil-cooled tube-bundle-reactors.

Zonal activation of molecular carbon dioxide and hydrogen over dual sites Ni-Co-MgO catalyst for CO2 methanation: Synergistic catalysis of Ni and Co species

An in-depth mechanism in zonal activation of CO2 and H2 molecular over dual-active sites has not been revealed yet. Here, Ni-Co-MgO was rationally constructed to elucidate the CO2 methanation mechanism. The abundant surface nickel and cobalt components as active sites led to strong Ni-Co interaction with charge transfer from nickel to cobalt. Notably, electron-enriched Coδ− species participated in efficient chemisorption and activation of CO2 to generate monodentate carbonate. Simultaneously, plentiful available Ni0 sites facilitated H2 dissociation, thus CO2 and H2 were smoothly activated at zones of Coδ− species and Ni0, respectively. Detailed in situ DRIFTS, quasi situ XPS, TPSR, and DFT calculations substantiated a new formate evolution mechanism via monodentate carbonate instead of traditional bidentate carbonate based on synergistic catalysis of Coδ− species and Ni0. The zonal activation of CO2 and H2 by tuning electron behaviors of double-center catalysts can boost heterogeneous catalytic hydrogenation performance.

Unravelling the potential of fibrous silica zirconia catalyst for CO methanation in energy production

In this contemporary era of rapid progress, the global demand for energy has reached unprecedented levels, placing considerable strain on existing energy supplies. To address this challenge, synthetic or substituted natural gas (SNG) has emerged as a groundbreaking energy source attained through the methanation reaction of hydrogen and carbon monoxide (CO). This paper unveils a successful synthesis method for fibrous silica zirconia (FSZr) exploiting the microemulsion procedure, subsequently applied in the CO methanation process. The catalyst underwent comprehensive characterization using advanced techniques, including Fourier Transform Infrared (FTIR) spectroscopy, Field-Emission Scanning Electron Microscopy (FESEM), x-ray diffraction (XRD), and N2 adsorption-desorption. The experimental results clearly demonstrate the exceptional catalytic performance of FSZr when compared to commercially available ZrO2. At a temperature of 500 ºC, FSZr achieved a CO conversion and CH4 yield of 20.76% and 11.52%, respectively. The remarkable achievements are credited to FSZr’s distinct fibrous structure, expansive surface area, and exceptional basic characteristics. The heightened surface area facilitates better access to reactive sites, while the strong basic properties enable easier adsorption of the reactant. These combined factors significantly enhanced the effectiveness of the CO methanation procedure. These findings underscore the significance of fibrous morphology in zirconia catalysts for CO methanation, presenting a promising avenue for further research and insights into meeting the global energy demands efficiently.

Development of Ni-doped A-site lanthanides-based perovskite-type oxide catalysts for CO2 methanation by auto-combustion method.

Engineering the interfacial interaction between the active metal element and support material is a promising strategy for improving the performance of catalysts toward CO2 methanation. Herein, the Ni-doped rare-earth metal-based A-site substituted perovskite-type oxide catalysts (Ni/AMnO3; A = Sm, La, Nd, Ce, Pr) were synthesized by auto-combustion method, thoroughly characterized, and evaluated for CO2 methanation reaction. The XRD analysis confirmed the perovskite structure and the formation of nano-size particles with crystallite sizes ranging from 18 to 47 nm. The Ni/CeMnO3 catalyst exhibited a higher CO2 conversion rate of 6.6 × 10-5 molCO2 gcat -1 s-1 and high selectivity towards CH4 formation due to the surface composition of the active sites and capability to activate CO2 molecules under redox property adopted associative and dissociative mechanisms. The higher activity of the catalyst could be attributed to the strong metal-support interface, available active sites, surface basicity, and higher surface area. XRD analysis of spent catalysts showed enlarged crystallite size, indicating particle aggregation during the reaction; nevertheless, the cerium-containing catalyst displayed the least increase, demonstrating resilience, structural stability, and potential for CO2 methanation reaction.

Combining in-situ synchrotron and electron microscopy techniques to study NiFe catalysts for CO2 methanation

Combining in-situ synchrotron and electron microscopy techniques to study NiFe catalysts for CO2 methanation

Producing methane from dry municipal solid wastes: A complete roadmap and the influence of char catalyst

The lack of standardized products is a key hindrance to the widespread commercialization of municipal solid wastes (MSW) pyrolysis technology. In this paper, a cost-effective roadmap employing pyro-gasification and methanation processes is developed, with CH4-rich gas as the target product. In this roadmap, a two-stage catalytic conversion of “MSW → syngas → CH4-rich gas” was realized using MSW char, a by-product of the pyrolysis process as the catalyst/catalyst carrier. The results showed that, in the pyro-gasification stage, a syngas yield of 1.3 L/gMSW could be obtained at 800 °C and a steam-to-MSW mass ratio of 0.4, with a H2 fraction reaching 56.6 vol%. The effective conversion of MSW to syngas was attributed to the superior catalytic activity of the MSW char. By comparing the catalytic activity and structural characteristics of the chars produced from various waste components, it could be determined that the high catalytic activity of the char required both active minerals derived from contaminated plastics and residue, and an appropriate proportion of carbon matrix from the biomass components in MSW. The gasified MSW char (G-MSWC), co-produced with the syngas, served as a carrier for the subsequent methanation catalyst. Due to the activation effect of steam during the syngas production stage, the pore structure of G-MSWC was improved and its defect density also increased. Consequently, G-MSWC demonstrated enhanced Ni–C interaction, facilitating the methanation activity. The final product from the methanation stage achieved a CH4 concentration of 52.9 vol%, and a CH4 yield of 11.25 mol/kgMSW. The above findings demonstrate the feasibility of the complete roadmap from MSW to CH4 and provide valuable guidance for decentralized MSW management based on pyrolysis technology.

Synergistic effect of Ni and NiO in hydrogen reduction for CO methanation

The synthesis of methane from syngas represents a pivotal technology in the artificial synthesis of natural gas, with the study of methanation catalysts being a fundamental aspect of this process. Extensive research has focused on CO methanation using Ni/Al2O3 catalysts; however, enhancements in catalyst stability and low-temperature activity are still required. This research investigated the structure of Ni/Al2O3 under H2 reduction at varying temperatures and the catalytic performance in natural gas synthesis (SNG) through CO methanation. It was observed that a higher reduction temperature resulted in nickel species agglomeration. Notably, Ni catalysts reduced at 600 °C demonstrated optimal CO conversion and CH4 selectivity under the tested conditions. Characterization studies uncovered a synergistic effect between Ni and NiO species, which was most effective for catalytic activity under hydrogen reduction at 600 °C but only at an appropriate reduction temperature. These insights are significant for the advancement of Ni/Al2O3 methanation catalysts in natural gas production.

Electronic regulation of MoS2 edge sites by d electron transfer of Ni or Co to improve the activity of CO sulfur-resistant methanation

The catalyst modified by the difference of transition metal d orbital electrons is a promising strategy to promote its catalytic activity, which has been extensively studied in heterogeneous catalysis. Herein, Ni and Co transition metals were used to modify the MoS2 catalyst and promote activity for sulfur-resistant CO methanation. Characterization results indicated that Ni or Co atoms could be successfully doped into the edge-site of MoS2, which generated more S-vacancy at Mo-edge site and enhanced sulfur-resistant CO methanation activity. The roles of Ni and Co doping in improving activity were explored based on DFT calculation. It was found that Ni or Co could modify the electronic structure, weaken the strength of their interaction with edge S atoms and promote the spontaneous formation of more S vacancies at Mo edge sites. This leads to enhancing the adsorption of CO and weakening the bonding energy between C-O, which implied the facilitation of CO hydrogenation. Moreover, the modified Ni(Co)-Mo-S active sites facilitate the rate-determining step of CO hydrogenation activation to form *CHO species, which contributes to the enhanced activity for sulfur-resistant CO methanation. This work provides an attractive method for modifying MoS2 catalysts for sulfur-resistant CO methanation.

CO2 methanation over open cell foams prepared via chemical conversion coating

In the framework of the CO2 utilization, and of the integration of renewable energy sources into the power generation scenario, the methanation reaction plays a key role, being the core of the power-to-gas, or power-to-X, processes. Structured catalysts are widely recognized for being particularly promising in exothermic processes, as they ensure a better thermal management of the heat generated within the system. In recent years, the application of metallic structures has spread. Nevertheless, the functionalization of these structures via washcoating procedure has several disadvantages. Herein, it is highlighted the potential of ceria chemical-conversion coating (CCC) as technique for the preparation of methanation catalysts, and optimize the Ni deposition procedure on such structures. In this work, the suitability of the obtained catalysts for CO2 methanation was evaluated in several operating conditions, obtaining CO2 conversion as high as 70 % below 400 °C with the most promising sample. In a first analysis, it was demonstrated that the catalysts prepared through the CCC technique can be applied in the CO2 methanation systems. In addition, through a kinetic analysis it was highlighted that the preparation method could be a key parameter for the selectivity of the process, driving the system towards a direct CO2 methanation or to the CO-path mechanism, therefore further studies should be performed to better explore this aspect.

Tuning the selectivity of photothermal CO2 hydrogenation through photo-induced interaction between Ni nanoparticles and TiO2

Photothermal CO2 hydrogenation into value-added chemicals driven by abundant solar energy is a promising and sustainable approach for achieving carbon neutralization. Herein, we demonstrate the photo-induced interaction between Ni nanoparticles and TiO2 support (Ni@TiO2) for maneuvering the selectivity of photothermal CO2 hydrogenation. According to experimental characterizations and theoretical simulations, the formed strong metal-support interaction between Ni and TiO2 can significantly enhance the adsorption of key intermediate *CO for further hydrogenation, thus tuning the CO2 hydrogenation pathway toward CH4. Consequently, the Ni@TiO2 catalyst exhibits a CH4 production rate of 286.5 mmol gcat−1 h−1 with an 81.8% selectivity under full-spectrum solar light irradiation. Moreover, in situ experimental characterizations and theoretical calculations suggest that photothermal CO2 hydrogenation over Ni@TiO2 undergoes a stepwise hydrogenation pathway to methane. This work offers insights into a simple approach for designing efficient nonprecious metal-based CO2 methanation catalysts.

Heterogeneous Catalysts for Carbon Dioxide Methanation: A View on Catalytic Performance

CO2 methanation offers a promising route for converting CO2 into valuable chemicals and energy fuels at the same time as hydrogen is stored in methane, so the development of suitable catalysts is crucial. In this review, the performance of catalysts for CO2 methanation is presented and discussed, including noble metal-based catalysts and non-noble metal-based catalysts. Among the noble metal-based catalysts (Ru, Rh, and Pd), Ru-based catalysts show the best catalytic performance. In the non-noble metal catalysts, Ni-based catalysts are the best among Ni-, Co-, and Fe-based catalysts. The factors predominantly affecting catalytic performance are the dispersion of the active metal; the synergy of the active metal with support; and the addition of dopants. Further comprehensive investigations into (i) catalytic performance under industrial conditions, (ii) stability over a much longer period and (iii) activity enhancement at low reaction temperatures are anticipated to meet the industrial applications of CO2 methanation.

Visualizing the Birth and Monitoring the Life of a Bimetallic Methanation Catalyst.

Well-defined bimetallic heterogeneous catalysts are not only difficult to synthesize in a controlled manner, but their elemental distributions are also notoriously challenging to define. Knowledge of these distributions is required for both the as-synthesized catalyst and its activated form under reaction conditions, where various types of reconstruction can occur. Success in this endeavor requires observation of the active catalyst via in situ analytical methods. As a step toward this goal, we present a composite material composed of bimetallic nickel-ruthenium nanoparticles supported on a protonated zeolite (Ni-Ru/HZSM-5) and probe its evolution and function as a photoactive carbon dioxide methanation catalyst using in situ X-ray absorption spectroscopy (XAS). The working Ni-Ru/HZSM-5, as a selective and durable photothermal CO2 methanation catalyst, comprises a corona of Ru nanoparticles decorating a Ni nanoparticle core. The specific Ni-Ru interactions in the bimetallic particles were confirmed by in situ XAS, which reveals significant electron transfer from Ni to Ru. The light-harvesting Ni nanoparticle core and electron-accepting Ru nanoparticle corona serve as the CO2 and H2 dissociation centers, respectively. These Ni and Ru nanoparticles also promote synergistic photothermal and hydrogen atom transfer effects. Collectively, these effects enable an associative CO2 methanation reaction pathway while hindering coking and fostering high selectivity toward methane.