Density functional theory study of propane steam reforming on Rh-Ni bimetallic surface: Sulfur tolerance and scaling/Brønsted-Evans-Polanyi relations

Enhanced sulfur tolerance on binary Rh-Ni metals is examined for the propane steam reforming process on close packed metal surfaces of Rh, Ni, Rh₁Ni₂, and Rh₂Ni₁ with and without co-adsorbed S atoms. Scaling and Brønsted-Evans-Polanyi (BEP) correlations are constructed from density functional theory (DFT) methods. The combined use of these methods produces significant errors among these similar metal surfaces; however, BEP relations applied within reaction types are reliable across Rh, Ni, and binary Rh-Ni surfaces with and without co-adsorbed S atoms. The potential energy surface of propane steam reforming, estimated using the BEP correlations, shows that the C-C cleavages of CHC^*, CH₃CC^* and CH₂C^* along with the O addition to CH^* are kinetically significant elementary steps. Three of these steps show only slight barrier increases with co-adsorbed S on the Rh₂Ni₁ surface, suggesting an energetic explanation for enhanced S tolerance. The average poisoning effect by the presence of co-adsorbed sulfur for bond breaking is minimized on binary Rh-Ni metals, suggesting a high sulfur resistance can be induced using a bimetallic formulation of Rh and Ni.