Comparative study of the kinetics of methane steam reforming on supported Ni and Sn/Ni alloy catalysts: The impact of the formation of Ni alloy on chemistry

We report the results of detailed kinetic studies for methane steam reforming on supported Ni and Sn/Ni surface alloy catalysts. The kinetic data were interpreted in terms of mechanism-based overall rate expression. We show that the activation of Csingle bondH bonds in methane is the rate-controlling step on both catalysts. Isotopic CH4/CD4 labeling studies were performed to independently verify the proposed mechanism. The role of Sn is to displace Ni atoms from under-coordinated sites on Ni particles and to move the critical reaction channels to more abundant well-coordinated sites. We show that previously observed increased resistance to carbon deactivation of Sn/Ni compared to monometallic Ni in hydrocarbon reforming reactions can be attributed to the Sn-induced lowering in the binding energy of carbon on low-coordinate sites, which serve as carbon nucleation centers, and to an enhanced propensity of Sn/Ni to oxidize carbon surface species. The conclusions derived from the experimental studies are in agreement with DFT calculations.