Methane Activation Research Articles

Introduction to integrated approaches for methane activation

Kenichi Shimizu, Wataru Ueda & Hua Song introduce the Catalysis Science & Technology themed collection on Integrated approaches for methane activation.

Mechanistic study of a coke-resistance Ni/ZrO2 catalyst for dry reforming of methane under external electric fields: a combined first-principles and microkinetic modeling study

Positive electric fields enhanced the DRM reactivity on Ni16/ZrO2 by promoting methane activation and CHx oxidation, while negative electric fields increased carbon deposition resistance due to advantageous CO2 activation.

Probing the structure–property relationships of supported copper oxide nanoclusters for methane activation

Amorphous metal-oxide nanoclusters are investigated using DFT and machine learning for selective oxidation of methane.

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.

Tailored Platinum Group Metal/Spinel Oxide Catalysts for Dynamically Enhanced Methane Oxidation.

A combined experimental and molecular modeling study identifies a family of spinel oxides that in combination with PGM (platinum group metals) provide enhanced methane oxidation activity. With a reduction in greenhouse gas (GHG) emissions urgently needed, there is renewed interest in the use of natural gas vehicles (NGVs) and engines (NGEs) for transportation, commerce, and industrial applications. NGVs and NGEs emit less CO2 than their petroleum-derived counterparts but may emit uncombusted methane, an even more potent GHG. For stoichiometric engines, methane oxidation catalysts containing PGM and spinel oxide in layered architectures offer increased methane oxidation activity and lower light-off temperatures (T50). The reducible spinel oxide has direct and indirect roles that are effectively described by the bulk oxygen vacancy formation energy (Evac). We apply density functional theory (DFT) to identify several earth-abundant, cobalt-rich spinel oxides with favorable Evac, shown to correlate with dynamic oxygen storage capacity (DOSC) and CO and H2 oxidation activity. We experimentally rank-order the DFT-identified spinel oxides in combination with Pt+Pd for their methane oxidation activity measurements, under both time-invariant and modulated feed conditions. We show good agreement between the activity and the DFT-computed reducibility of the spinel oxide. The findings suggest spinel reducibility is a key factor in achieving enhanced low-temperature methane conversion, enabled through a balance of methane activation on the PGM sites and subsequent oxidation of the intermediates and byproducts on spinel oxides. In agreement with its computationally predicted Evac, NiCo2O4 was confirmed to have the highest DOSC and lowest T50 among the tested spinel samples.

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.

Niobium Modification of CeO2 Tuning Electron Density of Nickel-Ceria Interfacial Sites for Enhanced CO2 Methanation.

CO2 methanation has attracted considerable attention as a promising strategy for recycling CO2 and generating valuable methane. This study presents a niobium-doped CeO2-supported Ni catalyst (Ni/NbCe), which demonstrates remarkable performance in terms of CO2 conversion and CH4 selectivity, even when operating at a low temperature of 250 °C. Structural analysis reveals the incorporation of Nb species into the CeO2 lattice, resulting in the formation of a Nb-Ce-O solid solution. Compared with the Ni/CeO2 catalyst, this solid solution demonstrates an improved spatial distribution. To comprehend the impact of the Nb-Ce-O solid solution on refining the electronic properties of the Ni-Ce interfacial sites, facilitating H2 activation, and accelerating the hydrogenation of CO2* into HCOO*, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis and density functional theory (DFT) calculations were conducted. These investigations shed light on the mechanism through which the activity of CO2 methanation is enhanced, which differs from the commonly observed CO* pathway triggered by oxygen vacancies (OV). Consequently, this study provides a comprehensive understanding of the intricate interplay between the electronic properties of the catalyst's active sites and the reaction pathway in CO2 methanation over Ni-based catalysts.

Increase of the Catalytic Activity of Molten Salts by Doping: Methane Activation

Increase of the Catalytic Activity of Molten Salts by Doping: Methane Activation

Systematic Assessment of the Catalytic Reactivity of Frustrated Lewis Pairs in C-H Bond Activation.

Unreactive C-H bond activation is a new horizon for frustrated Lewis pair (FLP) chemistry. This study provides a systematic assessment of the catalytic reactivity of recently reported intra-molecular FLPs on the activation of typical inert C-H bonds, including 1-methylpyrrole, methane, benzyl, propylene, and benzene, in terms of density functional theory (DFT) calculations. The reactivity of FLPs is evaluated according to the calculated reaction thermodynamic and energy barriers of C-H bond activation processes in the framework of concerted C-H activation mechanisms. As for 1-methylpyrrole, 14 types of N-B-based and 15 types of P-B-based FLPs are proposed to be active. Although none of the evaluated FLPs are able to catalyze the C-H activation of methane, benzyl, or propylene, four types of N-B-based FLPs are suggested to be capable of catalyzing the activation of benzene. Moreover, the influence of the strength of Lewis acid (LA) and Lewis base (LB), and the differences between the influences of LA and LB on the catalytic reactivity of FLPs, are also discussed briefly. This systematic assessment of the catalytic activity of FLPs should provide valuable guidelines to aid the development of efficient FLP-based metal-free catalysts for C-H bond activation.

Non‐oxidative Methane Activation over Molybdenum and Tungsten Nitride Catalysts

AbstractIn this study, molybdenum (Mo), tungsten (W), and mixed metal oxide and ‐nitride catalysts are synthesized via incipient wetness impregnation on silica support (SBA‐15) with a total target metal loading of 4 wt %. The effect of the Mo : W ratio on the non‐oxidative methane conversion, product selectivity, and coke formation is evaluated. The reduced Mo/SBA‐15 and MoW/SBA‐15 catalysts show higher CH4 conversion activity to benzene (selectivity of ~75.5 %) than for ethylene (selectivity of ~9.5 %) with a rather fast coke formation rate of 19–24 mgCoke gCat−1 h−1 without a clear influence of the Mo : W ratio. In contrast, the metal nitrides have a much smaller coke formation rate. The smallest rate of 0.45 mgCoke gCat−1 h−1 is achieved for the WN/SBA‐15 sample, which increases with the molybdenum content to 4.7 and 8.6 mgCoke gCat−1 h−1 for the MoWN(5 : 1) and MoN/SBA‐15 catalysts, respectively. There seems to be a yet unknown but negative correlation between the coke formation rate and the number of silanamine functional groups formed during the catalyst nitridation (Si−OH→≡Si−NH2→≡Si−NH−Si≡). The C2H4 selectivity is significantly increased with the relative amount of tungsten, with the highest C2H4 selectivity of 63 % for mixed‐metal nitride catalyst containing Mo : W ratio of 1 : 5. While the Mo/SBA‐15 the MoN/SBA‐15 achieve a C2H4 selectivity of less than 10 %.

Tuning CO adsorption states via enhanced metal-support interaction for boosting CO2 methanation activity of Ru/rutile-TiO2

Understanding the correlation between metal–support interactions (MSIs) and the adsorption states of reaction intermediates is critical for developing heterogeneous catalysts. To modulate MSIs and CO adsorption states, various Ru/Ti1-xCrxO2 catalysts were prepared by Cr3+ cation doping and used for CO2 methanation compared to the rutile TiO2-supported Ru catalyst (Ru/r-TiO2). The activity followed the order: Ru/Ti0.95Cr0.05O2 > Ru/Ti0.97Cr0.03O2 > Ru/Ti0.87Cr0.13O2 ≫ Ru/r-TiO2. The best Ru/Ti0.95Cr0.05O2 catalyst possessed CO2 turnover frequency (TOF) value at 200 °C 10.2 times higher than that on the Ru/r-TiO2. Cr3+ doping in the lattice of r-TiO2 support led to the Ru/Ti0.95Cr0.05O2 with higher dispersion of Ru and enhanced MSIs. A linear-CO*-II intermediate formed on the Ru/Ti0.95Cr0.05O2 with higher C-O vibrational frequency (2003 cm−1) than the linear-CO*-I at 1972 cm−1 on the Ru/r-TiO2, and the blue-shifted CO possessed higher activity for CO hydrogenation to CH4. The higher activity of the linear-CO* were accounting for the much higher TOF value of the Ru/Ti0.95Cr0.05O2. The strength of MSIs was proved to be highly correlated with CO adsorpton states including the balance of the strength of Ru-C and C-O bonds, which were found to be a crucial factor for the activity of supported Ru-based catalysts for CO hydrogenation.

Study of ceria-composite materials for high-temperature CO2 capture and their ruthenium functionalization for methane production

A set of Dual Function Materials (DFMs) was prepared to seize the CO2 from a rich feed gas and to in-situ convert it to methane (synthetic natural gas). Specifically, ruthenium-ceria composite materials were synthesized through successive impregnation depositions on two high surface area supports, namely Al2O3 and ZSM-5. Cerium oxide has both the roles of CO2 adsorbent and promoter support for ruthenium, which represents the active component for methanation. Three different quantities of ceria (10, 20, and 30 wt%) were dispersed onto the solid supports, and the adsorption capacities of the ceria-based materials were studied at different temperatures (150, 200, and 250 °C) at atmospheric pressure. The samples exhibiting the best results in terms of CO2 adsorption (30 wt% CeO2/Al2O3 and 30 wt% CeO2/ZSM-5) were subsequently impregnated to obtain ruthenium-loaded catalysts (2 wt% Ru). These functionalized materials were characterized by XRD, N2 physisorption at − 196 °C, TPDRO, ICP-MS, XPS, FESEM, HRTEM, and FT-IR. Then, cyclic experiments of CO2 adsorption and methanation were performed, simulating a real use of the catalysts at 250 °C and atmospheric pressure. The deposition of ruthenium-ceria on a high surface area support was found to be crucial for maintaining the methanation activity of this catalytic system under cyclic CO2 adsorption-hydrogenation conditions. The Al2O3-supported ruthenium-ceria catalyst adsorbed a lower amount of CO2 (ca. 200 μmol g−1 per each cycle) with respect to the zeolite-supported sample (ca. 300 μmol g−1); nevertheless, the former material presented the best methanation performances, thanks to an intermediate ruthenium-ceria interaction, yielding a maximum of 51% of CO2 converted and producing up to 111 μmol g−1 of CH4.

Transitioning from hydrogen to methane in biorefineries: A sustainable route to clean energy and chemicals

This review discusses the sustainable transformation of low-quality hydrocarbon fuels, such as biomass-derived bio-oil, into valuable chemicals and clean fuels by introducing the concept of "methanotreating" that uses methane as a hydrogen source for the deoxygenation of bio-oils, thereby addressing environmental concerns associated with conventional hydrogen production. We explore the challenges of methane activation and its potential in biomass upgrading, highlighting the importance of catalyst selection and composition. Methanotreating is a promising and sustainable method for producing high-quality fuels and chemicals, with a deoxygenation performance of over 95%. This present work calls for further research and development in catalyst design and application to advance this innovative approach toward a greener and more efficient energy future.

Investigation of the promotion effect of metal oxides on the water-gas shift reaction activity over Pt-MOx/CeO2 catalysts for aqueous phase reforming

Aqueous phase reforming (APR) of methanol is a potential pathway for the effective hydrogen production under relatively mild conditions. The Pt/CeO2 and a series of Pt-MOx/CeO2 (M = Fe, Cr, Mg, Mn) catalysts were prepared by sequential impregnation method and their APR reaction performances were studied. The catalyst properties including valence state of the promoters, the amount of oxygen vacancies, the metal distributions, the adsorption properties of CO and the acidity/basicity of catalysts were characterized and analyzed by XPS, XRD, TEM, CO-TPD, NH3-TPD, CO2-TPD, etc. It was found that the addition of MOx weakened the Pt-CeO2 interaction and promoted the generation of Ptδ+ species with lower valence state, which contribute to the C–H bond cleavage and facilitate methanol conversion. The highest hydrogen production (164.78 mmol) and relatively low CO and CH4 selectivities were obtained over the Pt-MgO/CeO2, while the highest CH4 selectivity was obtained over the Pt-CrOx/CeO2 (2.21%). Over the Pt/CeO2 and Pt-MOx/CeO2 (M = Fe, Cr, Mg, Mn) catalysts, CO2/CH4 ratio correlated well with the catalyst basicity, indicating that the basicity promotes the dissociation adsorption of H2O as well as the water-gas shift (WGS) reaction activity and decreases the methanation activity.

Methane adsorption and dissociation mechanism on the WC(001) surface: a first-principle calculation

The conversion of methane in catalysis fields has aroused much attention for its abundant distribution in nature and it is environment-friendly. However, the C–H chemical breaking is a major challenge and requires proper catalysts for methane activation. Using first-principle calculations, we systematically explore the atomic configuration, interaction strength, dehydrogenation process and electronic properties of methane on noble metal Pt(111) and isoelectronic transition metal carbide WC(001) surface. The adsorption strength of methane activation on the WC(001) surface is stronger and the barrier of C–H bond breaking is smaller than that of the Pt(111) surface. Moreover, the oxygen concentration ranging from 40% to 60% coverage on the WC(001) surface benefits the methane activation and the energy barrier decreased to 0.26 ∼ 0.57 eV. The larger charge transfer emerges at the interface between methane and the WC(001) surface with or without oxygen coverage comparable to the Pt(111) surface. Our theoretical results can provide vital guidance for experimental synthesis conditions of methane activation and the transition metal carbide application in catalysts.

Glycerol-assisted dynamic hydrothermal synthesis of nickel phyllosilicate for enhanced CO2 methanation: Synergistic effect of stirring and viscous solvent

To address the shortcomings of poor convection and product agglomeration of the static hydrothermal method, the dynamic hydrothermal method together with the viscous solvent-assisted dynamic hydrothermal method were proposed to synthesize Ni-phyllosilicate in this work. Stirring seemed to be powerful to accelerate the synthesis with significant increase of Ni content from 11.80 wt% (static synthesis) to 23.13 wt% (dynamic synthesis). The further modification of glycerol increased the shearing force to exfoliate the Ni-phyllosilicate nanosheets during dynamic synthesis, whose thickness could reach 1.17 nm with improved metal utilization ratio after reduction. As a result, the activity of CO2 methanation was enhanced with large TOFCO2 of 3.5 × 10−2 s−1 and small Ea of 65.13 kJ·mol−1. In situ DRIFTS analysis confirmed the existence of high actively intermediate of m-HCOO− and *CO, which could be further hydrogenated into CHx species. In short, the synergistic effect of dynamic stirring and glycerol modification drove the enhancement of catalytic activity, and also provided the possibility of large-scale production of Ni-phyllosilicate using hydrothermal method.

Co-aromatization of light alkanes over Mo/ZSM-5: How the presences of CH4 and C2H6 & C3H8 influence the aromatization of each other

The chemical inertness of methane is a significant bottleneck for its direct conversion into value-added light aromatics. However, co-feeding higher hydrocarbons with methane produces intermediates that facilitate the participation of methane in aromatization. This synergistic effect has typically been observed under conditions that do not allow the conversion of methane without any co-reactants (over non-Mo-based catalysts at temperatures below 650 ℃). Therefore, the interaction between methane and higher hydrocarbons remains unexplored under conditions that allow methane activation. In this study, we explored the behavior of co-reactants in the direct aromatization of simulated shale gas (a mixture of methane, ethane, and propane) over Mo/ZSM-5. Our aim was to comprehend the complex co-aromatization system under conditions optimized for rigorous activation of methane, which leads to a considerable production of aromatics. The majority of reaction indices in the shale gas aromatization system were governed by the presence of ethane and propane, which were represented by a rapid catalytic lifetime cycle. Mathematical calculations, based on experimentally derived C and H balances, revealed an unexpected anti-synergy within the components of shale gas where the conversion of methane to aromatics was partially suppressed by the presence of ethane and propane. These findings expand the understanding of the complex yet desirable shale gas aromatization system, and also highlight the need for the development of new catalysts capable of further enhancing the activity of methane among the reactants.

Small Cobalt Nanoparticles Favor Reverse Water‐Gas Shift Reaction Over Methanation Under CO2 Hydrogenation Conditions**

AbstractCobalt‐based catalysts are well‐known to convert syngas into a variety of Fischer–Tropsch (FTS) products depending on the various reaction parameters, in particular particle size. In contrast, the reactivity of these particles has been much less investigated in the context of CO2 hydrogenation. In that context, Surface organometallic chemistry (SOMC) was employed to synthesize highly dispersed cobalt nanoparticles (Co‐NPs) with particle sizes ranging from 1.6 to 3.0 nm. These SOMC‐derived Co‐NPs display significantly different catalytic performances under CO2 hydrogenation conditions: while the smallest cobalt nanoparticles (1.6 nm) catalyze mainly the reverse water‐gas shift (rWGS) reaction, the larger nanoparticles (2.1–3.0 nm) favor the expected methanation activity. Operando X‐ray absorption spectroscopy shows that the smaller cobalt particles are fully oxidized under CO2 hydrogenation conditions, while the larger ones remain mostly metallic, paralleling the observed difference of catalytic performances. This fundamental shift of selectivity, away from methanation to reverse water‐gas shift for the smaller nanoparticles is noteworthy and correlates with the formation of CoO under CO2 hydrogenation conditions.

Small Cobalt Nanoparticles Favor Reverse Water-Gas Shift Reaction Over Methanation Under CO2 Hydrogenation Conditions.

Cobalt-based catalysts are well-known to convert syngas into a variety of Fischer-Tropsch (FTS) products depending on the various reaction parameters, in particular particle size. In contrast, the reactivity of these particles has been much less investigated in the context of CO2 hydrogenation. In that context, Surface organometallic chemistry (SOMC) was employed to synthesize highly dispersed cobalt nanoparticles (Co-NPs) with particle sizes ranging from 1.6 to 3.0 nm. These SOMC-derived Co-NPs display significantly different catalytic performances under CO2 hydrogenation conditions: while the smallest cobalt nanoparticles (1.6 nm) catalyze mainly the reverse water-gas shift (rWGS) reaction, the larger nanoparticles (2.1-3.0 nm) favor the expected methanation activity. Operando X-ray absorption spectroscopy shows that the smaller cobalt particles are fully oxidized under CO2 hydrogenation conditions, while the larger ones remain mostly metallic, paralleling the observed difference of catalytic performances. This fundamental shift of selectivity, away from methanation to reverse water-gas shift for the smaller nanoparticles is noteworthy and correlates with the formation of CoO under CO2 hydrogenation conditions.

Non-Functionalized Subnanometer Copper Nanoparticles for Low-Temperature Methane Activation

Non-Functionalized Subnanometer Copper Nanoparticles for Low-Temperature Methane Activation