Directed synthesis and characterization of supported bimetallic overlayer catalysts

Bimetallic catalysts have long been an important part of the catalysis industry due to their ability to improve various catalytic properties compared to their pure metal counterparts. Unfortunately, in many cases these bimetallic catalysts are simple alloys of the component metals, which results in a particle structure that may not provide optimum catalytic properties. Ever increasing first principles computation and single crystal studies have shown that pseudomorphic overlayers, systems containing a metallic monolayer deposited on a bulk second metal, can exhibit surface properties very different from either pure component. These studies indicate that the ability to synthesize supported pseudomorphic overlayers may yield catalysts with some combination of improved activity, selectivity, and poison resistance, as well as improved efficiency in the placement of expensive active metals.;In this dissertation, a method for supported bimetallic overlayer catalyst synthesis is presented. This method, directed deposition, was used to synthesize alumina-supported bimetallic overlayer Pd on Re (Re Pd) and Pt on Ni (Ni Pt) catalysts. Synthesis parameters were varied across several prepared catalysts in order to examine the effect of these parameters on the properties of the resultant catalysts. Hydrogen chemisorption, ethylene hydrogenation experiments, TEM, and EDS were used to characterize the synthesized catalysts. The results of characterization efforts suggest that the directed deposition technique can successfully be used to synthesize supported bimetallic overlayer catalysts, with the final surface coverage being dependent on a combination of synthesis conditions and metal surface properties. Further, the characterization efforts indicate that the surface properties of supported bimetallic overlayer catalysts correspond well with results from ideal single crystal studies and first principles computation. In particular, the heat of hydrogen adsorption on Re Pd catalysts notably decreased compared to pure Pd and Re catalysts, in agreement with single crystal and computational studies. The reaction mechanism for ethylene hydrogenation on Re Pd catalysts was found to be unchanged from a pure Pd catalyst, but overall activity was slightly decreased on Re Pd catalysts. A relationship between catalytic activity and hydrogen adsorption strength was also observed. The details of the synthesis method and characterization results will be discussed.