Effect of palladium on sulfur resistance in Pt-Pd bimetallic catalysts

The interactions of H-2 and H2S molecules with Pt-Pd bimetallic catalysts were investigated at the molecular level using a DFT (density functional theory) approach to better understand the structures and properties of active sites, and the relations between structural changes and sulfur resistance. It was found that when alloying the Pt catalyst with a small amount of Pd at a particular surface atomic ratio range, both H-2 and H2S showed different adsorption properties compared to those on monometallic Pt or I'd catalyst. The adsorptions of both H-2 and H2S were enhanced, but the adsorption energy of H-2 increased more than that of H2S, indicating that the adsorption of H2S became less favorable compared with H-2 on the bimetallic Pt-Pd catalyst surface. The desorption energy of hydrogen from monometallic Pt or Pd, as well as bimetallic Pt-Pd supported on zeolite, were calculated by temperature-programmed desorption (TPD), the values were compared against the DFT results to explain experimentally and theoretically why the bimetallic Pt-Pd catalyst has better sulfur resistance than monometallic Pt catalyst. Crown Copyright (C) 2007 Published by Elsevier B.V. All rights reserved.