Supported Vanadium Carbide Catalysts for Reverse Water Gas Shift and Methanol Steam Reforming: Activity, Stability, and Coking Pathways

High Resolution Image Download MS PowerPoint Slide A series of supported vanadium carbide (VC x ) catalysts were prepared, characterized, and tested for the carbon dioxide and methanol activation via the Reverse Water Gas Shift (RWGS) and Methanol Steam Reforming (MSR) reactions, respectively. Crystallite sizes of VC x ranging from 9 to 36 nm were obtained depending on the support used (γ-Al 2 O 3, SiO 2, CeO 2, ZrO 2 and TiO 2 ). In both reactions, the supported catalysts exhibited superior performance compared to the bulk VC x sample. In the RWGS reaction, all catalysts showed high CO selectivity, with VC x /Al 2 O 3 demonstrating the best performance and no significant deactivation after 100 h at 873 K. Under MSR conditions, VC x /ZrO 2 achieved the highest methanol conversion. However, all catalysts suffered from significant deactivation due to coke formation, with CH 4 as the main product instead of the desired H 2 and CO 2 from full steam reforming. Density Functional Theory (DFT) calculations revealed that methanol decomposition is more facile than CO 2 decomposition on both stoichiometric VC and carbon-deficient V 8 C 7 surfaces, particularly in the presence of carbon vacancies, leading to coke formation in the form of partially hydrogenated C x H y * species. These findings indicate that VC x catalysts are more susceptible to coking under MSR than RWGS conditions, in line with experimental observations, and highlight the critical role of the carbide surface structure and vacancy concentration in coke formation.