CO2 Methanation Research Articles

Electron Localization-Triggered Proton Pumping Toward Cu Single Atoms for Electrochemical CO2 Methanation of Unprecedented Selectivity.

Slow multi-proton coupled electron transfer kinetics and unexpected desorption of intermediates severely hinder the selectivity of CO2 methanation. In this work, a one-stone-two-bird strategy of pumping protons and improving adsorption configuration/capability enabled by electron localization is developed to be highly efficient for CH4 electrosynthesis over Cu single atoms anchored on bismuth vacancies of BiVO4 (Bi1-x VO4 ─Cu), with superior kinetic isotope effect and high CH4 Faraday efficiency (92%), far outperforming state-of-the-art electrocatalysts for CO2 methanation. Control experiments and theoretical calculations reveal that the bismuth vacancies (VBi ) not only act as active sites for H2 O dissociation but also induce electron transfer toward Cu single-atom sites. The VBi -induced electron localization pumps *H from VBi sites to Cu single atoms, significantly promoting the generation and stabilization of the pivotal intermediate (*CHO) for highly selective CH4 electrosynthesis. The metal vacancies as new initiators show enormous potential in the proton transfer-involved hydrogenative conversion processes.

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.

Plasma-Deposited CoO–(Carbon Matrix) Thin-Film Nanocatalysts: The Impact of Nanoscale p-n Heterojunctions on Activity in CO2 Methanation

Addressing the challenges associated with the highly exothermic nature of CO2 methanation, there is considerable interest in innovative catalyst designs on structural metallic supports. One promising solution in this regard involves thin films containing cobalt oxide within a carbon matrix, fabricated using the cold plasma deposition method (PECVD). The objective of this study was to search for a relationship between the molecular structure, nanostructure, and electronic structure of such films and their catalytic activity. The investigations employed various techniques, including X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), X-ray diffraction (XRD), UV-VIS absorption, and catalytic tests in the CO2 methanation process. Three types of films were tested: untreated as-deposited (ad-CoO), thermally post-treated (TT-CoO), and argon plasma post-treated (PT-CoO) films. Among these, TT-CoO exhibited the most favorable catalytic properties, demonstrating a CO2 conversion rate of 83%, CH4 selectivity of 98% at 400 °C, and stability during the catalytic process. This superior performance was attributed to the formation of nanoscale heterojunctions in the TT-CoO film, where p-type CoO nanocrystallites interacted with the n-type carbon matrix. This work provides compelling evidence highlighting the key role of nanoscale heterojunctions in shaping the properties of nanocatalysts in thermal catalysis. These findings suggest promising prospects for designing new catalytic systems by manipulating interactions at the nanoscale.

Effect of a Second Promoter on the Performance of a Potassium Doped Silica-Supported Cobalt Catalyst During CO2 Hydrogenation to Hydrocarbons

In this study, the promoting effects of ruthenium, palladium, and copper on the performance of a 15%Co-1%K/SiO2 catalyst were evaluated during CO2 hydrogenation in a fixed-bed reactor. Reactions were carried out at atmospheric pressure and 270 °C with H2/CO2 ratio of 3. All catalysts were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) and temperature-programmed reduction (TPR). Ruthenium, palladium and copper facilitated the reduction of cobalt oxides and increased cobalt dispersion. In terms of catalyst’s performance, ruthenium addition led to increased CO2 conversion and methane selectivity with a detrimental effect on C5+ hydrocarbons. Palladium also presented a similar pattern at lower loading but a drop in CO2 conversion and increased reverse water–gas shift activity were observed at 3 wt % Pd loading. Promoting with copper resulted in decreased activity, methane selectivity and C5+ hydrocarbons productivity with a much higher CO selectivity.Graphical

A comparative study of fibrous silica-based catalysts for improving methane production via CO2 methanation

The process of utilizing the greenhouse gas carbon dioxide (CO2) is crucial in addressing and reducing the impact of climate change. The CO2 methanation process, also known as the Sabatier reaction, is considered one of the appealing approaches since it provides synthetic natural gas (SNG), fulfilling the present needs. However, the CO2 methanation reaction demands an exceptionally effective catalyst capable of surpassing the energy barrier associated with eight proton-electron transfers from H2 molecules. Herein, the application of fibrous silica nanospheres along with the fibrous modification of mesostructured silica nanoparticles (MSN) towards CO2 methanation, called the Centre of Hydrogen energy silica (CHE-Si) and CHE-SM was reported. Both catalysts were successfully synthesized by utilizing micro-emulsion techniques and subsequently were characterized with x-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, and N2 adsorption-desorption. FTIR results revealed that CHE-SM possessed superior Si-OH and Si-O species than CHE-Si despite displaying low surface area and pore volume. Consequently, CHE-SM achieved above 50% CO2 conversion and CH4 yield at 500 °C while CHE-Si exhibited lower performance. This discrepancy in catalytic performance was due to the fact that CHE-SM was comprised of more active sites that could adsorb and dissociate CO2 and H2 reactants.

CO2 methanation over nickel-CeO2 catalyst supported on Al2O3: Different impregnation strategies and Ni-Ce ratios

Methanation of CO2 was studied over Ni-CeO2-based catalysts supported on Al2O3 prepared by two different strategies: simultaneous and successive impregnation. The CeO2 addition modifies the interaction of Ni with the support, improving the CO2 conversion and the selectivity to CH4. The catalyst synthesized by simultaneous impregnation of NiO and CeO2 was more active than the catalyst synthesized by successive impregnation. This behavior was associated with the contribution of both oxygen vacancies and Ni-O-Ce solid solution at the surface, inducing a superior reducibility and more labile moderate basic sites. Microstructural analysis confirms the proximity of Ni nanoparticles and CeO2 nanocrystallites, improving the extension of the Ni-CeO2 interface and the activity of the catalyst. The optimal composition of the Ni-CeO2based catalysts was established by testing several catalysts with Ni and Ce contents between 10 and 30 wt% and 10 to 20 wt%, respectively, prepared by simultaneous impregnation. An excellent catalytic performance was obtained for the catalyst with 15 wt% Ni and 15 wt% Ce supported on Al2O3, with high stability after 90 h at 375 °C. The catalytic behavior was explained by the high density of moderate basic sites and the fine-tuning of the Ni-CeO2 interactions.

Selective methanation of CO over HZSM-5 supported Ni and Ni–Ru catalysts

Under the synergistic effect of acid sites and active metal sites, Ni/HZSM-5 and Ni–Ru/HZSM-5 performed excellent CO removal properties and CO methanation selectivity.

Lattice capacity-dependent activity for CO2 methanation: crafting Ni/CeO2 catalysts with outstanding performance at low temperatures.

In the pursuit of understanding lattice capacity threshold effects of oxide solid solutions for their supported Ni catalysts, a series of Ca2+-doped CeO2 solid solutions with 10 wt% Ni loading (named Ni/CaxCe1-xOy) was prepared using a sol-gel method and used for CO2 methanation. The lattice capacity of Ca2+ in the lattice of CeO2 was firstly determined by the XRD extrapolation method, corresponding to a Ca/(Ca + Ce) molar ratio of 11%. When the amount of Ca2+ in the CaxCe1-xOy supports was close to the CeO2 lattice capacity for Ca2+ incorporation, the obtained Ni/Ca0.1Ce0.9Oy catalyst possessed the optimal intrinsic activity for CO2 methanation. XPS, Raman spectroscopy, EPR and CO2-TPD analyses revealed the largest amount of highly active moderate-strength alkaline centers generated by oxygen vacancies. The catalytic reaction mechanisms were revealed using in situ IR analysis. The results clearly demonstrated that the structure and reactivity of the Ni/CaxCe1-xOy catalyst exhibited the lattice capacity threshold effect. The findings offer a new venue for developing highly efficient oxide-supported Ni catalysts for low-temperature CO2 methanation reaction and enabling efficient catalyst screening.

Theoretical study of catalytic activity modifications in CO2 methanation induced by an electric field in solid-oxide cells

We performed DFT calculations for hydrocarbon species on Ni(111) with direct electric fields and co-adsorbed O atoms, respectively. The latter effect is dominant in NEMCA mechanism on CO2 methanation and the overall reaction accelerates in SOEC mode.

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.

Revisiting the mitigation of coke formation: Synergism between support & promoters' role toward robust yield in the CO2 reformation of methane

CO2 reformation of methane (CRM) and CO2 methanation are two interconnected processes with significant implications for greenhouse gas reduction and sustainable energy production for industrial purposes. While Ni-based catalysis suffers from poor stability due to coke formation or sintering, we report a super stable remedy. The active sites of mesoporous MgO were loaded using wet impregnation. The incorporation of Ni and promoters altered the physical features of the catalysts. Sm–Ni/MgO showed the smallest crystallite size, specific surface area, and pore volume. The Sm–Ni/MgO catalyst was selected as the most suitable candidate for CRM, with 82 ​% CH4 and H2/CO ratio of approximately 100 ​% and also for CO2 methanation with the conversion of carbon dioxide (82 ​%) and the selectivity toward methane reaches 100 ​% at temperatures above 300 ᵒC. Furthermore, the Sm–Ni/MgO catalyst was stable for 900 ​min of continuous reaction, without significant carbon deposition. This stability was largely due to the high oxygen mobility on the catalyst surface in the presence of Sm. Overall, we demonstrated the efficacy of using promoted Ni catalysts supported by mesoporous magnesia for the improved reformation of greenhouse gases.

Investigation of titania and ceria support effects in nickel catalyzed CO2 methanation

Spectroscopic characterization enables the study of the structure sensitivity of Ni based catalysts on TiO2 and CeO2 for CO methanation.

Variations in microbial community compositions and processes imposed under contrast geochemical contexts in Sicilian mud volcanoes, Italy.

Terrestrial mud volcanoes represent surface features of channels for subsurface methane transport and, therefore, constitute an important source of methane emission from natural environments. How microbial processes regulate methane emissions in terrestrial mud volcanoes has yet to be fully addressed. This study demonstrated the geochemical characteristics and microbial communities of four mud volcano and seep sites in two geological settings of Sicily, Italy. At sites within the accretionary wedge that exhibited higher methane and sulfate concentrations, the communities were dominated by members capable of catalyzing methane and sulfate metabolisms and organic degradation. In particular, both anaerobic and aerobic methanotrophs were abundant and their abundance distribution coincided with the geochemical transition. In contrast, the sites near Mount Etna were characterized by high fluid salinity, CO2, and low methane and sulfate concentrations, with communities consisting of halophilic organic degraders and sulfur metabolizers, along with a minor presence of aerobic methanotrophs. Substantial variations in community composition and geochemistry across spatial and vertical redox gradients suggest that physicochemical contexts imposed by the geology, fluid path, and source characteristics play a vital role in shaping community composition and cycling of methane, sulfur and organic carbon in Sicily mud volcanoes.

Accelerated design of nickel-cobalt based catalysts for CO2 hydrogenation with human-in-the-loop active machine learning.

Thermo-catalytic conversion of CO2 into more valuable compounds, such as methane, is an attractive strategy for energy storage in chemical bonds and creating a carbon-based circular economy. However, designing heterogeneous catalysts remains a challenging, time- and resource-consuming task. Herein, we present an interpretable, human-in-the-loop active machine learning framework to efficiently plan catalytic experiments, execute them in an automated set-up, and estimate the effect of experimental variables on the catalytic activity. A dataset with 48 catalytic activity tests was compiled from a design space of Ni-Co/Al2O3 catalysts with over 50 million potential combinations in only eight iterations. This small dataset was found sufficient to predict CO2 conversion, methane selectivity, and methane space-time yield with remarkable accuracy (R 2 > 0.9) for untested catalysts and reaction conditions. New experiments and catalysts were selected with this methodology, leading to experimental conditions that improved the methane space-time yield by nearly 50% in comparison to the previously obtained maximum in the dataset. Interpretation of the model predictions unveiled the effect of each catalyst descriptor and reaction condition on the outcome. Particularly, the strong predicted inverse trend between the calcination temperature and the catalytic activity was validated experimentally, and characterization implied an underlying structure-performance relationship. Finally, it is demonstrated that the deployed active learning model is excellently suited to predict and fit kinetic trends with a minimal amount of data. This data-driven framework is a first step to faster, model-based, and interpretable design of catalysts and holds promise for broader applications across catalytic processes.

Modulating the porosity of N-doped carbon materials for enhanced CO2 capture and methane uptake

Adding N dopants (melamine or urea) to biomass during activation modulates the porosity of activated carbons to enhance CO2 storage (up to 4.7 mmol g−1 at 1 bar and 25 °C) and methane uptake (0.42 g g−1 and 266 cm3 (STP) cm−3 at 25 °C and 100 bar).

Fluidized bed chemical looping for CO2 capture and catalytic methanation using dual function materials

CO2 capture from combustion flue gas combined to its catalytic hydrogenation to synthetic methane is considered as a promising technology in the field of Carbon Capture and Utilization (CCU). In this work, the integrated CO2 capture and methanation process was investigated in an innovative chemical looping configuration using dual function materials (DFMs) recirculated alternately between two interconnected bubbling fluidized bed reactors. By physically separating the CO2 capture step and the catalytic hydrogenation reaction in two coupled fluidized bed reactors it is possible to effectively control and independently optimize the operating temperature of each half cycle while running the process continuously. A high-performing Lithium-Ruthenium/Al2O3 was selected to investigate the effect of the specific temperature level for the CO2 capture and the methanation phases in the range 200 - 400 °C, checking the stability and repeatability of the CO2 sorption and catalytic performance over 5 repeated cycles for each operating condition. Subsequently, under the best conditions in terms of methanation performance, a similar Na-promoted dual function material was also tested. The DFMs performance appeared to be quite reproducible over the cycles, but it was subject to kinetic limitations, especially in the case of Na-Ru/Al2O3. Interestingly, the methane yield approached 100 % under the highest tested temperatures for the Li-based DFM. Despite some limitations due to the experimental purge phases of the lab-scale system, the study provides the proof-of-concept of the process which enables the possibility of decoupling the two steps with the aim of a large potential intensification.

Optimizing CO2 methanation: effect of surface basicity and active phase reducibility on Ni-based catalysts

CO2 methanation presents an intriguing avenue for utilizing carbon dioxide and generating methane as synthetic natural gas. Both reducibility and basicity of catalysts play a major role in catalytic performances improvement.

Tailoring the active phase of CoO-based thin-film catalysts in order to tune selectivity in CO2 hydrogenation.

In this study, we prepared CoO-based thin films deposited on Kanthal steel wire gauze meshes by plasma-enhanced chemical vapor deposition. X-ray photoelectron spectroscopy (XPS) analysis revealed a structure characterized by a combination of cobalt oxide and metallic cobalt embedded within a carbon matrix. Our primary objective was to gain insights into the roles of Co0 and CoO in CO2 hydrogenation reactions. To achieve this, the performance of the thin-film CoO-based catalyst with an initial atomic ratio of CoO/Co0 at 10.2 was compared with two series of the thin-film catalysts that underwent pre-reduction processes at 350 °C for durations of 30 and 60 minutes, resulting in atomic ratios of CoO/Co0 at 3.1 and 1.1, respectively. Subsequently, catalytic tests were conducted in a continuous flow stirred tank reactor operating at temperatures ranging from 250 °C to 400 °C. Our findings indicate that CoO plays a significant role in activating the CO2 methanation reaction which can be due to the high hydrogen coverage of CoO, while Co0 is the active phase in the reverse water-gas shift reaction. Results highlight the importance of oxidized cobalt for hydrogen adsorption and dissociation in CO2 hydrogenation for CH4 formation.

A hierarchical hollow Ni/γ-Al2O3 catalyst derived from flower-like Ni–Al layered double hydroxide with stable catalytic performance for CO2 methanation

A hierarchical hollow Ni/H-γ-Al2O3 catalyst composed of cross-linked γ-Al2O3 nanosheets exhibits high efficiency for CO2 methanation.

Synergistic effects of rare-earth and lanthanoid elements on P123-modified Ni-HiMO catalysts for enhanced CO2 methanation under thermal and DBD-assisted conditions

For the first time, Ni(Mg,Al)Ox catalysts were optimized by Pluronic P123 and Sc, Y, La, and Gd for enhanced thermal and DBD-assisted CO2 methanation.