Improving the Carbon Resistance of Ni-Based Steam Reforming Catalyst by Alloying with Rh: A Computational Study Coupled with Reforming Experiments and EXAFS Characterization

Supported nickel catalysts are widely used in hydrocarbon steam reforming for producing hydrogen. Carbon deposition is a major cause of Ni catalyst deactivation. In this work, supported Ni and Ni/Rh catalysts were synthesized and tested for liquid hydrocarbon steam reforming. Carbon analysis on the spent catalysts illustrates that the carbon deposition is significantly reduced with inclusion of Rh. Extended X-ray Absorption Fine Structure (EXAFS) analysis indicates close interactions between Ni and Rh atoms. Density functional theory (DFT) results show that a Ni/Rh alloy is thermodynamically more stable than Ni and Rh alone at the synthesis and reaction temperatures. Adsorption, diffusion, and oxidation of carbon atoms over Ni and Ni/Rh alloy surfaces were examined by DFT calculations. Alloying with Rh reduces the stability of deposited carbon atoms an clusters over both terraces and steps: of the catalyst Moreover, Rh addition enhances the competition of oxidation reactions against carbon deposition by altering the relative diffusion rates and bond formation rates of the two processes.