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

Abstract

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.