Performance For CO Methanation Research Articles

Self-dispersed bimetallic NiRu nanoparticles on CeO2 for CO2 methanation

Redispersing bimetallic active nanoparticles in a heterogeneous catalyst can significantly improve metal utilization and catalytic performance, but it is very challenging. In this work, we report a feasible method to redisperse large bimetallic NiRu particles (30–40 nm) on the CeO2 support into small alloyed NiRu nanoparticles (3–5 nm) in an Ar gas atmosphere (NiRu/CeO2-Ar). During the high-temperature treatment, Ru metal in big bimetallic NiRu particles migrated to the surface of small alloyed nanoparticles because of the metal-phase separation, forming more Ni−Ru metal interfaces. As a result, NiRu/CeO2-Ar showed much better catalytic performance in CO2 methanation than the pristine catalyst (NiRu/CeO2) and the catalysts treated in air, H2, and reactant gases, respectively. Experimental and theoretical calculation results reveal that the newly generated Ni−Ru metal interfaces are conducive to the adsorption of CO2 and further direct dissociation into CO*, thus enhancing the catalytic performance. This work provides a reliable strategy to redisperse bimetallic NiRu nanoparticles into small ones with more intermetallic interfaces.

Ni–Fe nanoparticles prepared using hydrotalcite precursors enhance the photocatalytic performance of CO2 methanation

A series of Fe-modified bimetallic hydrotalcite-like photocatalysts are prepared through co-precipitation containing amounts of M2+(NO3)2·6H2O (M2+ = Mg, Ni) and M3+(NO3)3·9H2O (M3+ = Al, Fe) with a fixed Ni content and a monometallic 25Ni/Al2O3 catalyst for comparison purpose. The main objective of this experimental work is to study the replacement of Al with Fe in the photocatalyst on the CO2 methanation performance under three different reaction conditions (dark, ultraviolet and visible illumination). Thus, the use of Fe as a promoter has been studied for improving the light adsorption capability of photocatalysts and the reducibility of active metals. However, the results showed that modification by Fe acting as active metal and as support modification, is less effective than modification by Al. Therefore, the effects of both the basicity and photothermal activation by plasmonic nanoparticles under ultraviolet and visible photocatalytic conditions improve the methane production compared to the reaction under dark conditions.

Supra-Photothermal CO2 Methanation over Greenhouse-Like Plasmonic Superstructures of Ultrasmall Cobalt Nanoparticles.

Improving the solar-to-thermal energy conversion efficiency of photothermal nanomaterials at no expense of other physicochemical properties, e.g., the catalytic reactivity of metal nanoparticles, is highly desired for diverse applications but remains a big challenge. Herein, a synergistic strategy is developed for enhanced photothermal conversion by a greenhouse-like plasmonic superstructure of 4 nm cobalt nanoparticles while maintaining their intrinsic catalytic reactivity. The silica shell plays a key role in retaining the plasmonic superstructures for efficient use of the full solar spectrum, and reducing the heat loss of cobalt nanoparticles via the nano-greenhouse effect. The optimized plasmonic superstructure catalyst exhibits supra-photothermal CO2 methanation performance with a record-high rate of 2.3 mol gCo -1 h-1 , close to 100% CH4 selectivity, and desirable catalytic stability. This work reveals the great potential of nanoscale greenhouse effect in enhancing photothermal conversions through the combination with conventional promoting strategies, shedding light on the design of efficient photothermal nanomaterials for demanding applications.

Boosting Low‐Temperature CO2 Hydrogenation over Ni‐based Catalysts by Tuning Strong Metal‐Support Interactions

AbstractRational design of low‐cost and efficient transition‐metal catalysts for low‐temperature CO2 activation is significant and poses great challenges. Herein, a strategy via regulating the local electron density of active sites is developed to boost CO2 methanation that normally requires >350 °C for commercial Ni catalysts. An optimal Ni/ZrO2 catalyst affords an excellent low‐temperature performance hitherto, with a CO2 conversion of 84.0 %, CH4 selectivity of 98.6 % even at 230 °C and GHSV of 12,000 mL g−1 h−1 for 106 h, reflecting one of the best CO2 methanation performance to date on Ni‐based catalysts. Combined a series of in situ spectroscopic characterization studies reveal that re‐constructing monoclinic‐ZrO2 supported Ni species with abundant oxygen vacancies can facilitate CO2 activation, owing to the enhanced local electron density of Ni induced by the strong metal‐support interactions. These findings might be of great aid for construction of robust catalysts with an enhanced performance for CO2 emission abatement and beyond.

Boosting Low-Temperature CO2 Hydrogenation over Ni-based Catalysts by Tuning Strong Metal-Support Interactions.

Rational design of low-cost and efficient transition-metal catalysts for low-temperature CO2 activation is significant and poses great challenges. Herein, a strategy via regulating the local electron density of active sites is developed to boost CO2 methanation that normally requires >350 °C for commercial Ni catalysts. An optimal Ni/ZrO2 catalyst affords an excellent low-temperature performance hitherto, with a CO2 conversion of 84.0 %, CH4 selectivity of 98.6 % even at 230 °C and GHSV of 12,000 mL g-1 h-1 for 106 h, reflecting one of the best CO2 methanation performance to date on Ni-based catalysts. Combined a series of in situ spectroscopic characterization studies reveal that re-constructing monoclinic-ZrO2 supported Ni species with abundant oxygen vacancies can facilitate CO2 activation, owing to the enhanced local electron density of Ni induced by the strong metal-support interactions. These findings might be of great aid for construction of robust catalysts with an enhanced performance for CO2 emission abatement and beyond.

Nanofibrous perovskite ceramics with in-situ exsolved Ni3Fe alloy nanoparticles for catalytic CO2 methanation

Exsolution is a promising method to prepare highly-dispersed and stable nanocatalysts, while exsolution efficiency is limited by the high temperature crystallization of parent perovskite ceramics, which leads to the low surface area of parent oxides for exsolution. The fibrous structure of ceramics shows highly-thermal stability, and this study employed the thermally-stable structure to realize the high efficiency of exsolved nanocatalysts from perovskites. Sr0.95Ti0.3Fe0.55Ni0.15O3-δ nanofibrous perovskites catalysts were prepared by electrospinning and subsequent calcination and reduction. The amount of exsolved Ni3Fe alloy nanoparticles increased with calcination temperature up to 1075 °C while the catalysts retained the nanofibrous structure. Further increasing calcination temperature to 1100 °C caused catalyst agglomeration. The Ni dissolution was also optimized by tuning the amount of Ni-doping to maximize catalyst activity. The nanofibrous catalysts demonstrated high and stable performance in CO2 methanation, and achieved the CO2 conversion and CH4 selectivity of 70.5% and 94.4% at 450 °C. Therefore, the merits of exsolution method have been realized over the nanofibrous perovskite catalysts.

A highly efficient Ni/3DOM-La2O2CO3 catalyst with ordered macroporous structure for CO2 methanation

The global focus on new energy sources and energy storage methods has prompted significant research interest. Ni-based catalysts for CO2 methanation have the potential for industrialization, but face challenges such as high-temperature sintering, carbon deposition, and unstable catalytic activity; of which similar problems exist in NH3 decomposition reactions. A 10%Ni/3DOM-La2O2CO3 catalyst, featuring a three-dimensional ordered macroporous (3DOM) structure, demonstrated competitive low-temperature catalytic performance in CO2 methanation through formate intermediates. Comprehensive characterizations revealed improved Ni dispersion and carbon deposition prevention due to the 3DOM structure, enhancing catalytic activity. This structural advantage also translated to improved performance in ammonia decomposition.

Unveiling the promotion effect of ethylenediamine on preparation of Ni/CeO2 catalyst for low-temperature CO2 methanation

Cost-effective CO2 conversion to value-added products remains a great challenge until present. Here, we have discovered that the ethylenediamine (EDA) assisted preparation of Ni/CeO2 catalyst remarkably promotes the CO2 methanation performance at low temperatures. The Ni/CeO2-EDA catalyst exhibits a CO2 conversion efficiency of 84% and a CH4 selectivity of 98% at 225 °C, and no visible decline of CO2 conversion is observed even after 70h of continuous reaction. The involvement of EDA is shown to effectively result in a more uniform distribution of Ni species, coupled with a reduction in particle size. In addition, the smaller particle size of Ni results in a rapid dissociative adsorption of hydrogen and H2 spillover. Accordingly, oxygen vacancies on the CeO2 surface are created and adequate H atoms are engendered for CO2 hydrogenation. Furthermore, both the formate and CO pathways occur simultaneously on the Ni/CeO2-EDA catalyst, enhancing the low-temperature methanation activity. Herein, the EDA-assisted strategy provides an effective methodology in terms of well-dispersion and highly active catalysts for low-temperature CO2 methanation.

Ni-based hydrotalcite-derived catalysts for enhanced CO2 methanation: Thermal tuning of the metal-support interaction

Metal-support interaction (MSI) is recognized as an important factor affecting catalyst activity in CO2 methanation, but a feasible strategy to adjust MSI during catalyst preparation is not yet very clear. Herein, we designed a series of Mg-Al hydrotalcites calcined at different temperatures as supports for Ni-based catalysts preparation and investigated the relationship between MSI and catalytic activity. Through various characterizations, it is confirmed that the MSI can be tailored by thermal treatment resulting from phase transformation, and Ni/MAO1000 (which has strong MSI) showed the highest activity for CO2 conversion (1821 mmolCO2 mol−1 Ni min−1). Furthermore, in-situ DRIFTS experiments and DFT calculations proved that methoxy/carbonyls are key intermediates and Ni(111) is the determined crystal plane to produce CH4. This work provides an effective way to tailor the MSI of Ni-based catalysts for enhanced performance in CO2 methanation.

Adjusting active sites and metal-support interactions of ceramic-loaded Pd/P-CeO2-Al2O3 coating to optimize CO2 methanation pathways

Adjusting the active sites and metal-support interactions (MSI) of catalytic coatings on foam ceramics is a desirable strategy to improve CO2 methanation performance. By using a three-dipping and one-roasting technique, a highly active Pd/P-CeO2-Al2O3 catalyst (HA-Pd/PCA) with uniform three-dimensional mesh-like pores and daisy-like clusters was created. As PdO that was embedded in oxygen vacancies of CeO2 was reduced, oxygen vacancies were released. Pd then interacted with lattice oxygen close to the oxygen vacancies to create a strong MSI effect in the form of electron transfer. This translates to better Pd dispersion and more effective activation of the hydrogen. Moreover, the path of the hydrogen spillover that was necessary to hydrogenate the CO2 adsorbed in oxygen vacancies was shortened. In terms of the presence of acid-base sites, oxygen species, and oxygen vacancies, HA-Pd/PCA provided significant advantages. Based on this, the rate of carbonate to formate increased and the conversion pathway changed from a single bidentate formate to a dual pathway comprising bidentate formate and monodentate formate. The consumption and regeneration of hydroxyl groups were kept in balance. The outcomes demonstrated that HA-Pd/PCA had ideal stability, 100 % CH4 selectivity, and 86 % CO2 conversion.

CO2 methanation over Ni nanoparticles inversely loaded with CeO2 and Cr2O3: Catalytic functions of metal oxide/Ni interfaces

Interfaces between active metal and metal oxide in a heterogenous catalyst often play an important role in catalysis. In this work, we intentionally synthesized a series of inverse CeO2-Cr2O3/Ni model catalysts with the formation of controlled CeO2-Ni and Cr2O3-Ni interfacial structures and investigated the roles of the oxide-metal interfaces in CO2 methanation performance through excluding the normal support effect. Experimental and DFT calculation results reveal that the formate pathway tends to occur on the catalyst with only CeO2-Ni interfaces. The Cr2O3-Ni interface formed after introducing Cr oxide alters the nearby CeO2-Ni interface by electron transfer through Ni, which brings an additional reaction pathway (CO pathway) on CeO2-Cr2O3/Ni. Furthermore, it shows a relatively lower CO2 absorption energy and activation energy barrier for CO2 dissociation to CO at the Cr2O3-Ni interface, favorable for CO2 activation and further hydrogenation, thus leading to excellent low-temperature activity.

Catalytic CO2 hydrogenation to produce methane over NiO/TiO2 composite: Effect of TiO2 structure

In this study, TiO2 was morphologically engineered into three distinct structures, namely three-dimensional microparticles (MPs), zero-dimensional nanoparticles (NPs) and one-dimensional nanowires (NWs) to examine the effect of structure on CO2 methanation. Firstly, thermodynamic analysis was conducted, whereby it was observed that CH4 production is favoured at low temperature. Higher temperature will cause the CH4 selectivity to drop, in turn increasing the formation of other side products such as CO, C2H6 and solid coke. Then, Ni loaded on three different TiO2 supports, namely 3D TiO2 microparticles (MPs), 0D nanoparticles (NPs) and 1D nanowires (NWs), were prepared. It was noticed that the NPs have the smallest support particle size, followed by NWs and MPs. Despite TiO2 NWs having a larger particle size than NPs, the 15% Ni/TiO2 NWs boasted a higher surface area, smaller NiO crystalline and particle size, which resulted in an augmented NiO dispersion. Superior CO2 methanation performance with CO2 conversion, CH4 yield and selectivity of 88.44%, 87.53% and 98.97%, respectively was achieved over 15% Ni/TiO2 NWs. The stability of the TiO2 NWs counterpart over a 40 hours reaction time was the best among the three samples. Spent catalyst analysis also indicated that 15% Ni/TiO2 NWs are highly resistant to catalyst deactivation and coke formation. The prolonged durability was attributed to the 1D wire-like structure, which promoted a higher dispersion of active sites, facilitating an intimate contact between catalyst and reactants. The ameliorated dispersion also mitigates catalyst deactivation via sintering and coke formation. The findings elucidated that the morphology of the catalyst is more influential in enhancing the hydrogenation reaction than the support size.

Robust Self‐Catalytic Reactor for CO2 Methanation Fabricated by Metal 3D Printing and Selective Electrochemical Dissolution

AbstractThe methanation of CO2 has been actively pursued as a practical approach to mitigating global climate change. However, the complexity of the catalyst development process has hindered the development of new catalysts for CO2 methanation; as a result, few catalysts are commercially available. Herein, a multifunctional self‐catalytic reactor (SCR) is prepared via metal 3D printing and selective electrochemical dissolution as a method to not only simplify the catalyst development process but also fabricate active catalysts for CO2 methanation. The combination of metal 3D printing and selective electrochemical dissolution is demonstrated as a feasible method to prepare active catalysts for the methanation of CO2 in a short time. In addition, the use of an electrochemical method enables the formation of galvanic cells on the SCR; these cells continuously generate active sites via self‐dissolution during a simple refresh process, resulting in high reusability of the SCR. The proposed method represents a new facile technique to fabricate highly reusable catalysts that exhibit superior performance for CO2 methanation, and the results provide a guideline for preparing metal 3D‐printed catalysts that will satisfy industrial demand.

Highly Efficient Photocatalytic CO2 Methanation over Ru-Doped TiO2 with Tunable Oxygen Vacancies

Solar-driven CO2 methanation is an imperative and promising approach to relieve the global warming and environmental crisis, yet remains a great challenge due to the low reaction efficiency, unsatisfactory selectivity and poor stability. In this work, we demonstrate a facile and efficient strategy to prepare Ru-doped TiO2 photocatalyst with tunable oxygen vacancies using the ascorbic acid as a reducing agent for the CO2 methanation reaction. The optimal Ru-TiO2-OV-50 exhibits a remarkable CH4 production rate of 81.7 mmol g−1 h−1 with a 100% CH4 selectivity under a 1.5 W cm−2 light illumination, which is significantly higher than commercial Ru/TiO2 and other reported catalysts. We reveal that the superior photocatalytic CO2 methanation performance is mainly due to the synergistic effect of Ru doping and TiO2 with tunable oxygen vacancies. Impressively, the light rather than thermal effect is confirmed as the main influencing factor by experimental studies. In addition, in situ spectroscopic technology is performed to investigate the CO2 methanation reaction pathway. This work will open an avenue to design and prepare highly efficient photocatalyst with tunable oxygen vacancies for CO2 conversion and other related applications.

Defect-Rich and Boron-Doped Al2O3-Supported Ru Nanocatalyst for Enhanced CO2 Methanation Activity

Presently, fabricating a stable and high-performance noble metal catalyst is still a challenging task due to the easy aggregation and growth of metal particles during heterogeneous catalysis reactions. In this regard, catalyst supports always can profoundly impact the metal dispersion and electronic interaction with active metal species, thereby significantly regulating the catalytic performance of catalysts. Herein, a new strategy for fabricating boron-doped alumina support with coordinatively unsaturated penta-coordinated Al3+ (Alpenta3+) sites via a micro-liquid-film reactor-assisted coprecipitation approach was developed. Accordingly, as-formed alumina could efficiently immobilize Ru atoms via the anchoring effect of the Alpenta3+ site to construct a supported Ru catalyst for CO2 methanation. An as-constructed Alpenta3+ site-rich and boron-doped Al2O3-supported Ru nanocatalyst exhibited a better catalytic performance in CO2 methanation along with a higher methane yield of 81.2% under reaction conditions (i.e., 350 °C, 0.1 MPa pressure, and gas hourly space velocity of 6000 mL·gcat–1·h–1), compared to other supported Ru ones over commercial alumina and defect-free alumina. It was demonstrated that the high catalytic performance was closely associated with the coexistence of surface-defective Alpenta3+ sites and B–O species, thereby facilitating the accommodation of active hydrogen species on the support during CO2 hydrogenation as well as the activation adsorption of CO2 at the medium-strength basic sites originating from surface B–O–Al structures. This work provides a new strategy to construct high-performance and stable supported noble metal catalysts through engineering alumina support with special defective structures and surface modification for the applications in advanced heterogeneous catalytic systems.

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-temperature CO2 methanation over Ru/CeO2: Investigation into Ru loadings

The in-depth study of reaction intermediates, especially metal-support interactions, has brought great promise and challenges to the application of Ru-based catalysts in CO2 methanation. In this study, catalysts with different Ru loadings were prepared by wet impregnation method using CeO2 as the support. It is found that 1%Ru/CeO2 had excellent low-temperature methanation activity compared with other catalysts. As the metal loading increases, the oxygen vacancy concentration of the catalyst shows a volcano-type trend and the metal-support interaction increases. In addition, in situ DRIFTS showed that the low-temperature conditions are conducive to the formation of CO intermediates, making the CO2 methanation pathway more inclined to proceed along the CO pathway; while high temperature conditions are conducive to the formation of HCOO* intermediates, making the CO2 methanation pathway more inclined to proceed along the HCOO* pathway. This study demonstrates the importance of precisely determining the influence of metal active sites on the interaction between metal supports and oxygen vacancies for identifying critical reaction pathway intermediates and predicting CO2 methanation performance.

Polymer-derived SiOC as support material for Ni-based catalysts: CO2 methanation performance and effect of support modification with La2O3.

In this study, we investigated Ni supported on polymer-derived ceramics as a new class of catalyst materials. Catalysts have to withstand harsh reaction conditions requiring the use of a support with outstanding thermal and mechanical stability. Polymer-derived ceramics meet these requirements and bring the additional opportunity to realize complex porous structures. Ni-SiOC and La-modified Ni-SiOC catalysts were prepared by wet impregnation methods with target concentrations of 5wt% for both metal and oxide content. Polymer-derived SiOC supports were produced using a photoactive methyl-silsesquioxane as preceramic polymer. Catalysts were characterized by N2-adsorption-desorption, XRD, SEM, H2-TPR, and in-situ DRIFTS. CO2 methanation was performed as a test reaction to evaluate the catalytic performance of these new materials at atmospheric pressure in the temperature range between 200°C and 400°C. XDR, H2-TPR, and in-situ DRIFTS results indicate both improved dispersion and stability of Ni sites and increased adsorption capacities for CO2 in La-modified samples. Also, modified catalysts exhibited excellent performance in the CO2 methanation with CO2 conversions up to 88% and methane selectivity >99% at 300°C reaction temperature. Furthermore, the pyrolysis temperature of the support material affected the catalytic properties, the surface area, the stability of active sites, and the hydrophobicity of the surface. Overall, the materials show promising properties for catalytic applications.

Catalytic Performance for CO Methanation over Ni/MCM-41 Catalyst in a Slurry-Bed Reactor

The Ni-based catalyst has been intensively studied for CO methanation. Here, MCM-41 is selected as support to prepare xNi/MCM-41 catalysts with various Ni contents and the catalytic performance for CO methanation in a slurry-bed reactor is investigated under different reaction conditions. The CO conversion gradually increases as the reaction temperature or pressure rises. As the Ni content increases, the specific surface area and pore volume of xNi/MCM-41 catalysts decrease, the crystallite sizes of metallic Ni increase, while the metal surface area and active Ni atom numbers firstly increase and then slightly decrease. The 20Ni/MCM-41 catalyst with the Ni content of 20 wt% exhibits the highest catalytic activity for CO methanation, and the initial CH4 yield rate is well correlated to the active metallic Ni atom numbers. The characterization of the spent xNi/MCM-41 catalysts shows that the agglomeration of Ni metal is accountable for the catalyst deactivation.

CO2 methanation over Ni/Al2O3-ZrO2 catalysts: Optimizing metal-oxide interfaces by calcinating-induced phase transformation of support

A new strategy to prepare the NiO/Al2O3-ZrO2 catalyst with various interfacial structures by inducing different phase transitions of Al2O3 and ZrO2 via varying the precursor calcination temperature was proposed, and their CO2 methanation performance was subsequently investigated. The characterization of the catalyst showed that Ni was prone to bonding with Al ion during the calcination process and forming NiAl2O4 or strong interaction between Al2O3 and NiO. The reduced metallic nickel (Ni0) and partially unreduced NiAl2O4 exist in the state of Ni-NiAl2O4/Al2O3-ZrO2, forming a multi-interface system of Ni-O-Al, Al-O-Zr, and Ni-O-Zr. Moreover, this supplies medium-strength adsorption sites that play a key role in CO2 activation. The in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFTS) analysis and catalytic activity revealed that the CO2 methanation was completed in a two-step coupling route of Reverse Water Gas Shift (RWGS) and CO methanation. The abundant interfaces of the catalyst effectively suppressed the sintering of Ni.