Ti-Si composite oxide-supported cobalt catalysts for CO2 hydrogenation

Hydrogenation of CO2 into Value-added Chemicals Using Solid-Supported Catalysts

Reducing CO2 emissions is an urgent global priority. In this context, several mitigation strategies, including CO2 tax and stringent legislation, have been adopted to halt the deterioration of the natural environment. Also, carbon recycling procedures undoubtedly help reduce net emissions into the atmosphere, enhancing sustainability. Utilizing Earth's abundant CO2 to produce high-potential green chemicals and light fuels opens new avenues for the chemical industry. In this context, many attempts have been devoted to converting CO2 as a feedstock into various value-added chemicals, such as CH4, lower methanol, light olefins, gasoline, and higher hydrocarbons, for numerous applications involving various catalytic reactions. Although several CO2-conversion methods have been used, including electrochemical, photochemical, and biological approaches, the hydrogenation method allows the reaction to be tuned to produce the targeted compound without significantly altering infrastructure. This review discusses the numerous hydrogenation routes and their challenges, such as catalyst design, operation, and the combined art of structure-activity relationships for the various product formations.

Cerium d-Block Element (Co, Ni) Bimetallic Oxides as Catalysts for the Methanation of CO2: Effect of Pressure

Nickel– and cobalt–cerium bimetallic oxides were used as catalysts for the methanation of CO2 under pressure. The catalysts’ activity increases with pressure and an increase of just 10 bar is enough to double the yield of methane and to significantly improve the selectivity. The best results were those obtained over nickel–cerium bimetallic oxides, but the effect of pressure was particularly relevant over cobalt–cerium bimetallic oxides, which yield to methane increases from almost zero at atmospheric pressure to 50–60% at 30 bar. Both catalyst types are remarkably competitive, especially those containing nickel, which were always more active than a commercial rhodium catalyst used as a reference (5wt.% Rh/Al2O3) and tested under the same conditions. For the cobalt–cerium bimetallic oxides, the existence of a synergetic interaction between Co and CoO and the formation of cobalt carbides seems to play an important role in their catalytic behavior. Correlation between experimental reaction rates and simulated data confirms that the catalysts’ behavior follows the Langmuir–Hinshelwood–Hougen–Watson kinetic model, but Le Chatelier’s principle is also important to understand the catalysts’ behavior under pressure. A catalyst recycle study was also performed. The results obtained after five cycles using a nickel–cerium catalyst show insignificant variations in activity and selectivity, which are important for any type of practical application.

Effect of Operating Temperature, Pressure and Potassium Loading on the Performance of Silica-Supported Cobalt Catalyst in CO2 Hydrogenation to Hydrocarbon Fuel

Potassium (1–5 wt.%)-promoted and unpromoted Co/SiO2 catalysts were prepared by impregnation method and characterized by nitrogen physisorption, temperature-programmed reduction (TPR), CO2 temperature-programmed desorption (TPD), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. They were evaluated for CO2 hydrogenation in a fixed bed reactor from 180 to 300 °C within a pressure range of 1–20 bar. The yield for hydrocarbon products other than methane (C2+) was found to increase with an increase in the operating temperature and went through a maximum of approximately 270 °C. It did not show any significant dependency on the operating pressure and decreased at potassium loadings beyond 1 wt.%. Potassium was found to enhance the catalyst ability to adsorb CO2, but limited the reduction of cobalt species during the activation process. The improved CO2 adsorption resulted in a decrease in surface H/C ratio, the latter of which enhanced the formation of C2+ hydrocarbons. The highest C2+ yield was obtained on the catalyst promoted with 1 wt.% of potassium and operated at an optimal temperature of 270 °C and a pressure of 1 bar.

Evolution of Water Diffusion in a Sorption-Enhanced Methanation Catalyst

Sorption-enhanced methanation has consequent advantages compared to conventional methanation approaches; namely, the production of pure methane and enhanced kinetics thanks to the application of Le Châtelier’s principle. In this paper, we address the question of the long-term stability of a sorption-enhanced methanation catalyst-support couple: Ni nanoparticles on zeolite 5A. Compared to most conventional methanation processes the operational conditions of sorption-enhanced methanation are relatively mild, which allow for stable catalyst activity on the long term. Indeed, we show here that neither coking nor thermal degradation come into play under such conditions. However, a degradation mechanism specific to the sorption catalysis was observed under cyclic methanation/drying periods. This severely affects water diffusion kinetics in the zeolite support, as shown here by a decrease of the water-diffusion coefficient during multiple cycling. Water diffusion is a central mechanism in the sorption-enhanced methanation process, since it is rate-limiting for both methanation and drying.

A short review of recent advances in CO2 hydrogenation to hydrocarbons over heterogeneous catalysts

CO2 hydrogenation to hydrocarbons is a promising way of making waste to wealth and energy storage, which also solves the environmental and energy issues caused by CO2 emissions. Much efforts and research are aimed at the conversion of CO2 via hydrogenation to various value-added hydrocarbons, such as CH4, lower olefins, gasoline, or long-chain hydrocarbons catalyzed by different catalysts with various mechanisms. This review provides an overview of advances in CO2 hydrogenation to hydrocarbons that have been achieved recently in terms of catalyst design, catalytic performance and reaction mechanism from both experiments and density functional theory calculations. In addition, the factors influencing the performance of catalysts and the first C-C coupling mechanism through different routes are also revealed. The fundamental factor for product selectivity is the surface H/C ratio adjusted by active metals, supports and promoters. Furthermore, the technical and application challenges of CO2 conversion into useful fuels/chemicals are also summarized. To meet these challenges, future research directions are proposed in this review.

Highly active Co–Al2O3-based catalysts for CO2 methanation with very low platinum promotion prepared by double flame spray pyrolysis

Alumina supported Co catalysts are often promoted with noble metals to improve their reducibility and provide a high number of metallic Co sites. A flame spray pyrolysis based approach for the preparation is described which allows a fine dispersion of Pt so that very low concentrations are necessary.

Effect of Mo-Doped Mesoporous Al-SSP Catalysts for the Catalytic Dehydration of Ethanol to Ethylene

The catalytic dehydration of ethanol to ethylene over the mesoporous Al-SSP and Mo-doped Al-SSP catalysts was investigated. The Al-SSP catalyst was first synthesized by the modified sol-gel method and then doped with Mo by impregnation to obtain 1% Mo/Al-SSP and 5% Mo/Al-SSP catalysts (1 and 5 wt% of Mo). The final catalysts were characterized using various techniques such as XRD, N2physisorption, SEM/EDX, TEM, and NH3-TPD. The catalytic activity for all catalysts in gas-phase ethanol dehydration reaction was determined at temperature range of 200°C to 400°C. It was found that the most crucial factor influencing the catalytic activities appears to be the acidity. The acid property of catalysts depended on the amount of Mo loading. Increased Mo loading in Al-SSP resulted in increased weak acid sites, which enhanced the catalytic activity. Besides acidity, the high concentration of Al at surface of catalyst is also essential to obtain high activity. Based on the results, the most suitable catalyst in this study is 1% Mo/Al-SSP catalyst, which can produce ethylene yield of ca. 90% at 300°C with slight amounts of diethyl ether (DEE) and acetaldehyde.

CO2methanation by Ru-doped ceria: the role of the oxidation state of the surface

CO₂methanation takes place through surface carbonate intermediates and depends on the degree of reduction of the ruthenium-doped ceria catalyst.

Solvent-mediated reduction of carbon dioxide in anionic complexes with silver atoms

The development of efficient routes toward sustainable fuel sources by electrochemical reduction of CO2 is an important goal for catalysis research. While these processes usually occur in the presence of solvent, solvation effects in catalysis are largely not understood or even characterized. In this work, mass-selected clusters of silver anions with CO2 serve as a model system for reductive activation of CO2 by a catalyst in the presence of a well-controlled number of solvent molecules. Vibrational spectroscopy and electronic structure calculations are used to obtain molecular-level information on the interaction of solvent with the catalyst-CO2 complex and the effects of solvation on one-electron reductive activation of CO2. Charge transfer from the silver catalyst to CO2 increases with increasing cluster size. We observe the coexistence of catalyst-ligand complexes with CO2 monomer and dimer anions, indicating that CO2-based charge carriers can exist in the presence of a silver atom.