XAFS characterization of Pt-Mo bimetallic catalysts for CO hydrogenation

Abstract

Molybdenum-platinum bimetallic catalysts supported on alumina exhibited high activities: in CO hydrogenation than supported monometallic catalysts of Mo or Pt, The structure of Mo-Pt bimetallic catalysts, which were prepared by incipient wetness impregnation of gamma-alumina with the variation of the order of Mo and Pt addition, was studied by XAFS and CO chemisorption. Since molybdenum contains overlapping contribution of the first and the second shells, EXAFS of these two shells and the firs shell of platinum was analyzed for the bimetallic catalysts. EXAFS showed equivocally the formation of bimetallic bonds between Mo and Pt for all bimetallic catalysts. For all bimetallic catalysts, molybdenum seemed to segregate to the surface irrespective of the sequence of the impregnation. Strong interaction of Mo atoms with the support was also identified with EXAFS and XANES for both monometallic Mo catalysts and bimetallic catalysts. Regarding the activities of CO hydrogenation, it was concluded that reduced Mo sites were responsible for the high activity and that Pt helped Mo sites become more reduced. (C) 1997 Academic Press.