Highly active K-promoted Cu/β-Mo2C catalysts for reverse water gas shift reaction: Effect of potassium

Polyoxometalate-HKUST-1 composite derived nanostructured Na-Cu-Mo2C catalyst for efficient reverse water gas shift reaction

Transforming CO2 to CO via reverse water-gas shift (RWGS) reaction is widely regarded as a promising technique for improving the efficiency and economics of CO2 utilization processes. Moreover, it is also considered as a pathway towards e-fuels. Cu-oxide catalysts are widely explored for low-temperature RWGS reactions; nevertheless, they tend to deactivate significantly under applied reaction conditions due to the agglomeration of copper particles at elevated temperatures. Herein, we have synthesized homogeneously distributed Cu metallic nanoparticles supported on Mo2C for the RWGS reaction by a unique approach of in situ carburization of metal-organic frameworks (MOFs) using a Cu-based MOF i.e. HKUST-1 encapsulating molybdenum-based polyoxometalates. The newly derived Na-Cu-Mo2C nanocomposite catalyst system exhibits excellent catalytic performance with a CO production rate of 3230.0 mmol gcat-1 h-1 with 100% CO selectivity. Even after 250 h of a stability test, the catalyst remained active with more than 80% of its initial activity.

An active, stable cubic molybdenum carbide catalyst for the high-temperature reverse water-gas shift reaction

Although technologically promising, the reduction of carbon dioxide (CO2) to produce carbon monoxide (CO) remains economically challenging owing to the lack of an inexpensive, active, highly selective, and stable catalyst. We show that nanocrystalline cubic molybdenum carbide (α-Mo2C), prepared through a facile and scalable route, offers 100% selectivity for CO2 reduction to CO while maintaining its initial equilibrium conversion at high space velocity after more than 500 hours of exposure to harsh reaction conditions at 600°C. The combination of operando and postreaction characterization of the catalyst revealed that its high activity, selectivity, and stability are attributable to crystallographic phase purity, weak CO-Mo2C interactions, and interstitial oxygen atoms, respectively. Mechanistic studies and density functional theory (DFT) calculations provided evidence that the reaction proceeds through an H2-aided redox mechanism.

Recent Advances in Hydrogenation of CO2 to CO with Heterogeneous Catalysts Through the RWGS Reaction

With the continuous increase in CO2 emissions, primarily from the combustion of coal and oil, the ecosystem faces a significant threat. Therefore, as an effective method to minimize the issue, the Reverse Water Gas Shift (RWGS) reaction which converts CO2 towards CO attracts much attention, is an environmentally-friendly method to mitigate climate change and lessen dependence on fossil fuels. Nevertheless, the inherent thermodynamic stability and kinetic inertness of CO2 is a big challenge under mild conditions. In addition, it remains another fundamental challenge in RWGS reaction owing to CO selectivity issue caused by CO2 further hydrogenation towards CH4 . Up till now, a series of catalysis systems have been developed for CO2 reduction reaction to produce CO. Herein, the research progress of the well-performed heterogeneous catalysts for the RWGS reaction were summarized, including the catalyst design, catalytic performance and reaction mechanism. This review will provide insights into efficient utilization of CO2 and promote the development of RWGS reaction.

Design of Cu/MoOx for CO2 Reduction via Reverse Water Gas Shift Reaction

CO2 reduction to CO as raw material for conversion to chemicals and gasoline fuels via the reverse water–gas shift (RWGS) reaction is generally acknowledged to be a promising strategy that makes the CO2 utilization process more economical and efficient. Cu-based catalysts are low-cost and have high catalytic performance but have insufficient stability due to hardening at high temperatures. In this work, a series of Cu-based catalysts supported by MoOx were synthesized for noble metal-free RWGS reactions, and the effects of MoOx support on catalyst performance were investigated. The results show that the introduction of MoOx can effectively improve the catalytic performance of RWGS reactions. The obtained Cu/MoOx (1:1) catalyst displays excellent activity with 35.85% CO2 conversion and 99% selectivity for CO at 400 °C. A combination of XRD, XPS, and HRTEM characterization results demonstrate that MoOx support enhances the metal-oxide interactions with Cu through electronic modification and geometric coverage, thus obtaining highly dispersed copper and more Cu-MoOx interfaces as well as more corresponding oxygen vacancies.

Unveiling the Origin of Alkali Metal (Na, K, Rb, and Cs) Promotion in CO2 Dissociation over Mo2C Catalysts

Molybdenum carbide (Mo2C) is a promising and low-cost catalyst for the reverse water−gas shift (RWGS) reaction. Doping the Mo2C surface with alkali metals can improve the activity of CO2 conversion, but the effect of these metals on CO2 conversion to CO remains poorly understood. In this study, the energies of CO2 dissociation and CO desorption on the Mo2C surface in the presence of different alkali metals (Na, K, Rb, and Cs) are calculated using density functional theory (DFT). Alkali metal doping results in increasing electron density on the Mo atoms and promotes the adsorption and activation of CO2 on Mo2C; the dissociation barrier of CO2 is decreased from 12.51 on Mo2C surfaces to 9.51−11.21 Kcal/mol on alkali metal-modified Mo2C surfaces. Energetic and electronic analyses reveal that although the alkali metals directly bond with oxygen atoms of the oxides, the reduction in the energy of CO2 dissociation can be attributed to the increased interaction between CO/O fragments and Mo in the transition states. The abilities of four alkali metals (Na, K, Rb, and Cs) to promote CO2 dissociation increase in the order Na (11.21 Kcal/mol) < Rb (10.54 Kcal/mol) < Cs (10.41 Kcal/mol) < K (9.51 Kcal/mol). Through electronic analysis, it is found that the increased electron density on the Mo atoms is a result of the alkali metal, and a greater negative charge on Mo results in a lower energy barrier for CO2 dissociation.