Molybdenum and tungsten carbides as catalysts for the reverse water gas shift reaction

For the sustainable utilization of carbon dioxide (CO 2 ), the development of an inexpensive, active, selective and highly stable catalyst is essential to overcome the economic challenges in its reduction to carbon monoxide (CO). Molybdenum and tungsten carbides-based materials are regarded as attractive catalysts for the reverse water gas shift RWGS reaction. This work began with a series of catalytic tests indicating that mixed Mo-W carbides behave essentially like blends of monocarbides Mo 2 C and WC. To establish a performance baseline, an in-depth evaluation of the two monometallic carbides was conducted enabling a precise assessment of their intrinsic activity and mechanistic behavior under RWGS conditions. The results revealed that Mo 2 C promoted the formation of both CH 4 and CO, while increasing the tungsten content gradually, enhances CO selectivity with decreasing reaction rate. Monometallic tungsten carbide WC achieved complete CO selectivity and maintained it even after 100 h exposure to harsh reaction conditions at 600 ˚C. In-situ DRIFTS and density functional theory (DFT) calculations revealed that WC can achieve 100 % CO selectivity through two distinct mechanisms on different facets, a concerted redox mechanism on WC (-100), and an associative mechanism on WC (101) facet where further hydrogenation of *CHO intermediate is kinetically unfavorable. Both pathways steer the reaction toward CO production and prevent the formation of undesired side product CH 4 . This work not only provides valuable insights into the role of metal carbide phases in catalytic performance but also contributes to the fundamental understanding of reaction mechanism. • CO 2 hydrogenation via the RWGS reaction studied over Mo 2 C, MoW x C and WC catalysts. • Tungsten addition to Mo 2 C improves CO selectivity. • DFT revealed competing adsorption of intermediates on Mo 2 C surface. • Tungsten monocarbide catalyzes the RWGS reaction via redox mechanism.