Methanation Reaction Research Articles

Integrated CO2 capture and utilisation: A promising step contributing to carbon neutrality

The release of CO2 into the atmosphere is problematic; however, it is an abundant, renewable, and inexpensive carbon resource. In the past, the environmental problems caused by excessive CO2 emissions, such as global warming and ocean acidification, have become increasingly severe. Carbon capture and utilisation (CCU) has drawn intensive interest due to its capacity to sequester CO2 and utilise it as a carbon source to produce high-value chemicals and fuels. However, state-of-the-art CCU exhibits poor economics and technological complexity due to extensive energy input, a multiple reactor configuration, and sorbent transfer between reactors for sorbent regeneration. Integrated CO2 capture and utilisation (ICCU) directly utilises CO2-containing exhaust gas and in situ upgrades them into valuable products in a highly intensified process, representing a more direct and promising path for CO2 emission control. A series of high-performance dual functional materials (DFMs) composed of catalytic and adsorbent sites have succeeded in various ICCU applications. In this account, we first briefly introduced the research background of ICCU technology and the motivation for developing various ICCU applications. Furthermore, we conducted a detailed description of ICCU technology from three aspects: ICCU-methanation, ICCU-dry reforming methane (DRM) and ICCU-reverse water gas shift reaction (RWGS). In particular, we have investigated the optimal adsorption and catalytic sites for specific reaction characteristics and have solved the problem of temperature matching between the adsorption and catalytic sites. In addition, The mechanism underlying ICCU technology has been explored, and the effect of interfering components on catalytic performance in real plant flue gases for future applications has also been analysed. Significantly, the catalyst stability was effectively improved by investigating the causes of catalyst deactivation. Finally, although the technology of in situ CO2 capture and conversion is still in its preliminary stages, we can see that current research results already indicate promising prospects. In-situ capture and conversion of CO2 into high-value-added chemical feedstock will be a very attractive application for reducing greenhouse gases in the atmosphere and recycling carbon resources. We are also committed to promoting the industrialisation and large-scale production of ICCU technology.

Cerium‐promoted Ni/SiO2 catalyst for CO methanation

AbstractCe‐promoted Ni catalysts were developed and applied in a CO methanation reaction. The 10%Ni/SiO2 catalyst exhibits poor initial CO conversion (32.8%) and rapid deactivation with the highest methane selectivity during CO the methanation reaction. In contrast, the 4%Ce–10%Ni/SiO2 catalyst shows dramatically increased initial CO conversion, which is up to 90.7%. Additionally, the apparent activation energy, Ea value, of 4%Ce–10%Ni/SiO2 was calculated to be 102.2 kJ/mol according to the Arrhenius equation, which is much lower than that of the 10%Ni/SiO2 catalyst, which was 139.1 kJ/mol. Based on various characterization results, it is found that the added Ce significantly improves the dispersion of the supported nickel, suppresses the sintering of nickel particles, and forms more adsorbed CO species of three‐fold carbonyl species, resulting in higher CO conversion and good stability during the CO methanation reaction.

CO2 methanation over Ni supported on Carbon–ZrO2: An optimization of the composite composition

Currently, the most common catalysts for CO2 methanation reaction are based on Ni supported on metal oxides. However, such catalysts require high operation temperatures and present stability issues, which have been tackled by the use of expensive metal oxides such as CeO2 or ZrO2.In this study, the decrease in the amount of ZrO2 in ZrO2-based catalysts was addressed through the preparation of composites of ZrO2 and carbon materials (activated carbon (AC) and carbon nanotubes (CNTs)). The optimization of the carbon:ZrO2 ratio demonstrated an optimal value of 50:50 in the case of AC:ZrO2, and 70:30 for CNT:ZrO2. With this composite composition, the possibility of enhancing the performance of the catalyst by functionalizing the carbon material was evaluated, and it was demonstrated that reduced AC (AC-R) with increased Lewis basic sites showed the best performance for AC-based composites, achieving a CO2 conversion of 79 % and CH4 selectivity of 98.9 % at 400 °C, whereas the catalysts supported on the pristine CNT:ZrO2 composite presented the highest CO2 conversion of 82.1 % and CH4 selectivity of 99.3 % at 400 °C.Notably, promotion with Fe was studied in the best performing support (CNT:ZrO2 (70:30) and it was shown that it enabled an improvement in terms of CO2 conversion and optimal temperature, achieving a CO2 conversion of 85 % and CH4 selectivity of 99.5 % at a lower temperature of 370 °C. This catalyst demonstrated to be highly stable for 70 h of time on stream with no apparent modifications on its chemical composition or microstructure.This work demonstrates that combining the properties of carbon materials and ZrO2 can be an interesting approach to obtain high performing catalysts for CO2 methanation.

Examination of Morphological and Chemical Properties of Ni-BZY Anodes and their Influence upon Methane Reactivity and Electrochemical Performance of Protonic-Ceramic Fuel Cells

Ni-BZY (yttrium-doped barium zirconate) has drawn recent interest for application in protonic ceramic fuel cells (PCFCs) due to BZY’s superior protonic conductivity and stability in reforming environments containing CO2 and H2O. Additionally, Ni and BZY form unique nano/microstructures thought to synergistically facilitate reforming. While PCFCs with Ni-BZY anodes have demonstrated stable long-term performance, little is known about the material’s transformations during operation and subsequent impact on electrochemical metrics. To address this knowledge gap, we constructed PCFCs consisting of Ni-BZY anodes sintered onto a ~600 μm BZY electrolyte complete with a LSCF/BCZY cathode. The electrochemical performance of these cells is compared at 600-700 °C while operating with humidified hydrogen, neat methane, and steam reformed methane (1CH4:1H2O). Insights into morphological and chemical changes are provided by pre- and post-mortem analysis of the anode via Raman spectroscopy, X-ray diffraction, and SEM. Phase transformations, agglomeration and coking all appeared to contribute to performance degradation.

Neodymium promoted ceria and alumina supported nickel catalysts for CO2 methanation reaction

Two series of catalysts containing 20 wt.% nickel, promoted with different amounts of neodymium from 1 to 10 wt.% were prepared by the impregnation method, using nano-CeO2 and γ-Al2O3 as supports. Ceria supported nickel catalysts showed high activity in CO2 methanation reaction and weak activity changes were observed with an increase in Nd content. X-ray diffraction, hydrogen chemisorption and transmission electron microscopy studies evidenced a decrease in the average size of nickel crystallites and an increase in the active surface area of catalysts. The temperature-programmed reduction, oxidation and CO2 desorption, XPS, Raman and in-situ FTIR spectroscopy indicated complex changes in the nature of their redox and base centres. Non-promoted alumina supported nickel catalyst despite higher surface area showed lower activity than similar catalyst with ceria as support. However, an introduction of Nd-promoter led to strong increase in their activity. Such effect was mainly ascribed to the increase in their basicity, facilitation of CO2 activation and subsequent transformation of the intermediate surface species to methane with participation of hydrogen atoms activated on metallic nickel crystallites.

Waste-derived chars as methanation catalyst support: Role of inorganics in the char and its guide to catalyst design

The municipal solid waste-derived biochar (MSWC) can be applied as a catalyst support for low-cost syngas methanation. However, the mechanism of the char support as a catalyst in methanation process remains unclear. Based on the similarity between the intrinsic inorganics present in the chars and the promoters used for methanation catalyst modification, the impacts of the inorganics in different waste-derived chars on the methanation reaction were investigated. The results showed that the acid-soluble inorganics in the MSWC significantly improved the methanation activity of the MSWC-supported Ni catalysts. The acid-soluble inorganics were proved to have the role of promoting the formation of suitable Ni/support interactions, improving the dispersion of the Ni species, and increasing the concentration of the basic sites on the catalyst’s surface. Compared with the MSWC, the biochar contained much more water-soluble alkali metal salts (up to 15–57% of ash), which may be detrimental to the methanation activity of the biochar-supported Ni catalysts by leading to increases in Ni particle size and the concentration of the strong basic sites on the catalyst’s surface, especially when existing alone. A new alkali–carbon index was created to evaluate the effect of the inorganics in the waste-derived char on the methanation activity of the char-supported catalyst. A higher alkali–carbon index reflects improved methanation activity. Thus, the findings of this study can provide quantitative guidance for designing suitable waste-derived char as methanation catalyst supports.

Graphene nanoplatelets promoted CoO-based catalyst for low temperature CO2 methanation reaction

Methanation of CO2 is an important reaction for reducing CO2 emissions in a power-to-gas system. Compared to cobalt supported on gamma-Al2O3, cobalt supported on graphene nanoplatelets (GNPs) showed significantly better performance for CO2 methanation. Cobalt supported on GNPs was capable of 15% conversion of CO2 to CH4 at temperatures below 250°C, compared to 5% for cobalt supported on Al2O3. In situ thermogravimetric analysis (TGA) demonstrated that the Co/GNP catalyst was stable to 400°C. The maximum catalyst mass-specific CH4 yield was obtained at a Co loading of 5wt% on GNPs; however, high Co loading on GNPs deactivated the reactivity of the Co/GNP catalyst. Transmission electron microscopy (TEM) demonstrated that 5wt% Co/GNPs had the smallest and most dispersed cobalt nanoparticles. Excessive loading of cobalt tended to form isolated large Co nanoparticles. X-ray photoelectron spectroscopy (XPS) and Raman spectrometry revealed that more CoO phases were maintained on the surface of 5wt% Co/GNPs, indicating that the interaction between the Co and the GNPs had more of an impact on cobalt’s redox capacity than did particle size, which ultimately affected cobalt’s active phase during the CO2 reduction process. Furthermore, Raman spectrometry demonstrated that Co loading led to an increase in graphene defects. Higher Co loading on GNPs resulted in fewer interfaces between Co and GNPs due to the agglomeration of Co nanoparticles.

Low-energy-consumption CO2 recovery by combining H2 sweeping and methanation with the conventional VTSA approach

To achieve carbon capture and utilization, low-energy-consumption CO2 recovery and conversion technologies are required. However, the majority of previous studies on CO2 capture and conversion have been conducted independently. Therefore, we developed a local carbon recycling system that links these two technologies. In this system, CO2 is recovered from combustion exhaust gases by physical adsorption, the recovered CO2 is converted to CH4 by methanation, and the produced CH4 is used as a fuel. During conversion of the recovered CO2 into CH4, the recovered gas can contain a mixture of CO2 and H2; thus, H2 can be supplied during the desorption process to lower the CO2 partial pressure in the CO2 adsorber (hereafter referred to as H2 sweep). In addition, methanation is an exothermic reaction that can supply heat to the CO2 adsorber. In this study, focusing on the energy consumption of the CO2 adsorber, the effect of combining these two approaches with the conventional vacuum temperature swing adsorption process was investigated. Since this system requires the effective use of the methanation reaction heat, a shell-and-tube CO2 adsorber containing zeolite 13X was constructed. By combining these two approaches for an exhaust gas with a CO2 concentration of 9.6%, a CO2 recovery ratio of 90% was achieved with an energy consumption of 0.9 GJ/t-CO2. Moreover, a superior CO2 recovery ratio of 99% was achieved with an energy consumption of 1.4 GJ/t-CO2, thereby constituting a higher CO2 recovery ratio with a lower energy consumption compared with conventional CO2 adsorption systems.

Ni Single Atoms Confined in Nitrogen-Doped Carbon Nanotubes for Active and Selective Hydrogenation of CO2 to CO

Developing efficient non-precious-metal catalysts capable of selectively converting CO2 into fuels and chemicals is desirable yet remains a challenge. Ni-based catalysts usually exhibit high activity in methanation reactions but low selectivity and stability in the reverse water-gas shift (RWGS) reaction. Herein, we report a Ni single-atom catalyst with Ni–Nx motifs confined in N-doped carbon nanotubes as an active, selective, and stable catalyst for the RWGS reaction, achieving almost 100% CO selectivity with a STY of 1.88 molCO gNi–1 h–1 at 500 °C and atmospheric pressure. In addition to weak CO adsorption, strong CO2 adsorption and weak H2 adsorption at the Ni–Nx active site were found to be responsible for the high catalytic activity and CO selectivity.

Activity of Nickel Supported Over Nanorod-Shaped Strontium Hydroxyapatite Catalysts in Selective Methanation of CO & CO2

Nickel modified strontium hydroxyapatite (Ni/Sr-HAP) supported catalysts are studied in selective methanation of CO/CO2. In this work, a new type of nano rod-shaped strontium hydroxyapatite-based catalysts with two different sizes and aspect ratios were prepared by sol–gel method and in next step, Ni precursor was wet impregnated i.e., denoted as Ni/Sr-HAP and Ni/Sr-HAP(F127). The catalytic tests were performed in CO and CO2 methanation reactions and evaluated the light-off temperatures curves (225–450 °C) under ambient pressure in a fixed-bed flow reactor. The physicochemical properties of the prepared catalysts were characterized by XRD, N2 physisorption, TEM, SEM, TPR, CO2/H2-TPD and H2-chemisorption techniques. From XRD analysis, both Ni/Sr-HAP and Ni/Sr-HAP(F127) were identified as the hydroxyapatite type structure with high crystallinity and very low intensity peaks corresponds to strontium phosphates as the main phase and structure. The TEM and SEM micrographs of Ni/Sr-HAP catalysts displayed a nano- rod shaped morphology with different dimensions and exhibited average Ni particle size of ~ 9.2 nm. While Ni/Sr-HAP(F127) shown the rod size in the length in the range of 100–250 nm and width in the range of 20–40 nm with average Ni particle size 5.7 nm. The F127 mediated support Sr-HAP synthesis i.e., Ni/Sr-HAP(F127) mesoporous catalyst possessed higher metal surface with smaller Ni particles size and possessed higher CO2 adsorption capacity. The medium strength basic sites of Ni/Sr-HAP catalyst played an important role in methanation reactions. Based on the characterization and the catalysts activity results, small sized nanorods of Ni/Sr-HAP(F127) is the most active and selective catalyst due to the higher Ni dispersion, higher amounts of medium basic sites, and reducibility character than the bigger nanorods based Ni/Sr-HAP catalyst.

Feed Effects on Water–Gas Shift Activity of M/Co3O4-ZrO2 (M = Pt, Pd, and Ru) and Potassium Role in Methane Suppression

Water–gas shift (WGS) is an industrial process to tackle CO abatement and H2 upgradation. The syngas (CO and H2 mixture) obtained from steam or dry reformers often has unreacted (from dry reforming) or undesired (from steam reforming) CO2, which is subsequently sent to downstream WGS reactor for H2 upgradation. Thus, industrial processes must deal with CO2 and H2 in the reformate feed. Achieving high CO2 or H2 selectivities become challenging due to possible CO and CO2 methanation reactions, which further increases the separation costs to produce pure H2. In this study, M/Co3O4-ZrO2 (M = Ru, Pd and Pt) catalysts were prepared using sonochemical synthesis. The synthesized catalysts were tested for WGS activity under three feed conditions, namely, Feed A (CO and steam), Feed B (CO, H2 and steam) and Feed C (CO, H2, CO2 and steam). All the catalysts gave zero methane selectivity under Feed A conditions, whereas the methane selectivity was significant under Feed B and C conditions. Among all catalysts, PtCZ was found to be the best performing catalyst in terms of CO conversion and CO2 selectivity. However, it still suffered with low but significant methane selectivity. This best performing catalyst was further modified with an alkali component, potassium to suppress undesirable methane selectivity. All the catalysts were well characterized with BET, SEM, TEM to confirm the structural properties and effective doping of the noble metals. Additionally, the apparent activation energies were obtained to showcase the best catalyst.

Microwave Inhibition of the Hydrogenation of CO2 for Methane Formation

The complex equilibria associated with the hydrogenation of CO2 to form valuable products are of considerable interest for the remediation of CO2. Due to the potential usefulness of these reactions, alternative methods of driving them more favorably using alternative energy sources, such as microwave radiation, are also of interest. We report here a study of the methanation reaction that yields CH4, which was studied under microwave and conventional convective heating conditions. An essential part of the science that arises from such studies is characterizing the microwave-specific effects on the reaction. From the determined equilibrium constants, we found that microwave radiation strongly inhibited the formation of CH4. The effective thermodynamic parameters obtained from a van’t Hoff plot reflect this inhibition. The enthalpy under microwave conditions is −38.63 kJ/mol, compared to −180.02 kJ/mol under conventional heating methods. Similarly, the free energy across the temperature range is less negative, suggesting a decrease in spontaneity under microwave conditions. We also observed a significant difference in the entropy, with entropy of −52 J/mol under microwave conditions and −206 J/mol under conventional conditions. This is consistent with prior observations that microwaves do not accelerate exothermic reactions. As discussed, this difference may arise from the microwave-driven dissociation of the reactant before CH4 bonds are made. Analysis of this system is of interest in understanding how the microwave inhibits the formation of the products of exothermic reactions. These results are of significance for understanding the broad area of microwave driven heterogeneous catalysis.

Effect of different valence metals doping on methane activation over La2O3(001) surface

La2O3 as a catalyst is used for oxidative coupling of methane (OCM) reactions due to its excellent stability and high C2 selectivity, but poor activity on methane dissociation limits its wide application. Different valence metals are doped on the La2O3(001) surface to improve the methane conversion activity, and the activation of methane on metal-doped La2O3(001) surfaces has been investigated via the density functional theory (DFT) calculations. The relationship between the valence states of doped metals and the methane conversion activities shows that doping low valence metals (Li, Na, K, Mg, Ca, Sr and Ba) and equivalent metals (Al, Ga, In) can significantly improve the conversion activity of methane. Among them, the activation energy of methane on the Li-La2O3(001) surface is the lowest, which is only 13.0 kJ/mol. However, doping of high valence metals (Zr, Nb, Re and W) cannot improve the CH4 dissociation activity. Furthermore, the relationships between surface oxygen vacancy formation energies, acid-base properties and the activation energies of CH4 have also been investigated. The results show that with the increase of metal valence state, the oxygen vacancy formation energy increases, while the dissociation activity of CH4 decreases. The introduction of alkali and alkaline earth metals increases the alkalinity of La2O3(001) surface, and the alkalinity of La2O3(001) doped with the alkali metal is stronger than that with the alkaline earth metal, exhibiting higher dissociation activity of CH4. Our research may provide a guide for improving methane conversion activity on La2O3 catalysts.

The atomic-level adjacent NiFe bimetallic catalyst significantly improves the activity and stability for plasma-involved dry reforming reaction of CH4 and CO2

The plasma technology can effectively reduce the high temperature (≥700 °C) reaction condition of dry reforming of methane (DRM) reaction. But the inevitable carbon deposition problem seriously hinders the progress of plasma-involved DRM reaction. In order to promote the carbon elimination reaction between the adsorbed CO2 and carbon deposition produced by CH4 cracking, we have developed an effective atomic-level adjacent NiFe bimetallic catalyst. Compared to the Ni-based monometallic catalyst, the atomic-level adjacent NiFe bimetallic catalyst shows high activity and excellent stability in the plasma-involved DRM reaction. The conversions of CO2 and CH4 are 80.5% and 73.8%, respectively. Meanwhile, the catalytic performance remains well stable during the 100 h time-on-stream evaluation. The atomic-level adjacent NiFe bimetals were characterized by XRD, TEM and EXAFS et al., which are responsible for the improved activities. Most importantly, the addition of Fe can increase the surface oxygen and enhance CO2 adsorption confirmed by XPS and CO2-TPD, which beneficial to improve the ability to convert carbon deposition and improve the stability of catalyst. This work provides a feasible synthetic strategy for designing the high activity and well stability catalyst for the plasma-involved DRM reaction.

Supercharged CO2 Photothermal Catalytic Methanation: High Conversion, Rate, and Selectivity.

To overcome the thermodynamic and kinetic impediments of the Sabatier CO2 methanation reaction, the process must be operated under very high temperature and pressure conditions, to obtain an industrially viable conversion, rate, and selectivity. Herein, we report that these technologically relevant performance metrics have been achieved under much milder conditions using solar rather than thermal energy, where the methanation reaction is enabled by a novel nickel-boron nitride catalyst. In this regard, an in situ generated HOB⋅⋅⋅B surface frustrated Lewis's pair is considered responsible for the high Sabatier conversion 87.68 %, reaction rate 2.03 mol gNi -1 h-1 , and near 100 % selectivity, realized under ambient pressure conditions. This discovery bodes well for an opto-chemical engineering strategy aimed at the development and implementation of a sustainable 'Solar Sabatier' methanation process.

Supercharged CO2 Photothermal Catalytic Methanation: High Conversion, Rate, and Selectivity

AbstractTo overcome the thermodynamic and kinetic impediments of the Sabatier CO2 methanation reaction, the process must be operated under very high temperature and pressure conditions, to obtain an industrially viable conversion, rate, and selectivity. Herein, we report that these technologically relevant performance metrics have been achieved under much milder conditions using solar rather than thermal energy, where the methanation reaction is enabled by a novel nickel‐boron nitride catalyst. In this regard, an in situ generated HOB⋅⋅⋅B surface frustrated Lewis's pair is considered responsible for the high Sabatier conversion 87.68 %, reaction rate 2.03 mol gNi−1h−1, and near 100 % selectivity, realized under ambient pressure conditions. This discovery bodes well for an opto‐chemical engineering strategy aimed at the development and implementation of a sustainable ‘Solar Sabatier’ methanation process.

Boosting the generation of key intermediate methyl radical (CH3•) in OCM reaction on magnesium oxide catalysts by regulating the electronic state of the active site

Methyl radical (CH3•) is the critical precursor to generate C2 hydrocarbons in oxidative coupling of methane (OCM) reaction. It is crucial to explore how to efficiently generate CH3• and reveal the intrinsic principles behind it. In this study, we select MgO with a relatively simple structure as the research object, and probe the effects of the electronic state of active site on the CH3• generation by the density functional theory (DFT) calculation. The results show that the pure MgO with the different crystal surfaces as the benchmark models exhibit poor catalytic performance for CH3• generation; while Li doped MgO surface or subsurface that have the electron-deficient of active sites, exhibit excellent catalytic performance for it, which is attributed to that the electron-deficient of active sites are easier to receive electron of H and thereby promote the efficient generation of CH3•; pure MgO surface or subsurface with oxygen vacancy as well as Li doped MgO surface or subsurface with oxygen vacancy as the contrast models that have the electron-rich of active sites, exhibit poor catalytic performance. It can be obtained that the active site with electronic-deficient state is the key to the efficient generation of CH3•. The study can provide some guidance for designing high efficient OCM catalysts.

Comprehensive experimental study on supercritical water gasification of oilfield sludge: Effect of operation parameters, and catalysts on the products

Supercritical water gasification (SCWG) was adopted to treat oilfield sludge and produce syngas. The effect of temperature (400–450 °C), reaction time (30–90 min) and catalyst addition on syngas production and residual products during SCWG of oilfield sludge was studied. When increasing SCWG temperature from 400 to 450 °C with reaction time of 60 min, the H2 yield and the selectivity of H2 increased significantly from 0.53 mol/kg and 75.53% to 0.98 mol/kg and 78.09%, respectively. It is noteworthy that when the reaction time was too long, CO2 and CO were converted to CH4 with the consumption of H2 via methanation reaction. The addition of Ni/Al2O3 catalyst can substantially promote the production of high-quality syngas from SCWG of oilfield sludge. The H2 yield and its selectivity at 450 °C and 60 min were as high as 1.37 mol/kg and 84.05% with 10Ni/Al catalyst. Moreover, the catalysts with bimetal loading (Fe–Ni, Rb–Ni or Ce–Ni) were found to be beneficial for improving gasification efficiency, H2 yield, and the degradation of organic compounds. Among them, 5 wt% Rb on 10Ni/Al catalyst performed the best catalytic activity for SCWG at 450 °C and 60 min, which had the highest H2 yield of 1.67 mol/kg and selectivity of 86.09%. More than 90% of total organic carbon in sludge was decomposed after the SCWG with all the catalysts. These findings indicated that catalytic SCWG is a promising alternative for efficiently dealing with oilfield sludge.

Tuning the hydrogenation of CO2 to CH4 over mechano-chemically prepared palladium supported on ceria

CO2 methanation reactivity, reaction mechanism, and surface structure were investigated on a mechanochemically prepared Pd/CeO2 catalyst (PdAcCeO2-M), where an oxidative pretreatment (-o) increased methane yield by a factor of two compared to a reductive pretreatment (-h). Methanation rates were maintained for over 48 h and further increased upon oxidative regeneration treatments. The surface species of both PdAcCeO2-M-o and PdAcCeO2-M-h were explored via in situ CO2 and CO hydrogenation DRIFTS, where CO hydrogenation effectively models the dissociative CO2 mechanism (CO2 → CO → CH4). PdAcCeO2-M-o yielded distinct Pd-CO adsorption and the absence of monodentate carbonate at ∼ 1400 cm−1, while AP-XPS showed that PdAcCeO2-M-o yielded a unique Pdδ+ contribution at 335.9 eV. By gaining insights from various in situ spectroscopic techniques, and by breaking the CO2 hydrogenation mechanism into piecewise steps, a deeper understanding of the direct CO2 reduction towards methane and CO over mechanochemically prepared Pd/CeO2 catalysts was obtained.

Synergistic Catalysis at the Ni/ZrO2–x Interface toward Low-Temperature CO2 Methanation

The CO2 methanation reaction, which achieves the carbon cycle and gains value-added chemicals, has attracted much attention, but the design and exploitation of highly active catalysts remain a big challenge. Herein, zirconium dioxide-supported Ni catalysts toward low-temperature CO2 methanation are obtained via structural topological transformation of NiZrAl-layered double hydroxide (LDH) precursors, which have the feature of an interfacial structure (Ni-O-Zr3+-Vö) between Ni nanoparticles and ZrO2-x support (0 < x < 1). The optimized catalyst (Ni/ZrO2-x-S2) exhibits exceptional CO2 conversion (∼72%) at a temperature as low as 230 °C with a ∼100% selectivity to CH4, without obvious catalyst deactivation within a 110 h reaction at a high gas hourly space velocity of 30,000 mL·g-1·h-1. Markedly, the space-time yield of CH4 reaches up to ∼0.17 ·gcat-1·h-1, which is superior to previously reported Ni catalysts evaluated under similar reaction conditions. Both in situ/operando investigations (diffuse reflectance infrared Fourier transform spectroscopy and X-ray absorption fine structure) and catalytic evaluations substantiate the interfacial synergistic catalysis at the Ni/ZrO2-x interface: the Zr3+-Vö facilitates the activation adsorption of CO2, while the H2 molecule experiences dissociation at the metallic Ni sites. This work demonstrates that the metal-support interface effect plays a key role in improving the catalytic behavior toward CO2 methanation, which can be extended to other high-performance heterogeneous catalysts toward structure-sensitive systems.