Exploration of the Structure and Activity of Bimetallic Catalysts for the Dechlorination of Chlorocarbons

There is increasing demand for technologies that can transform wastes, such as the chlorocarbon byproducts of many industrial reactions, into useful process intermediates or commercial products. While the conversion of chlorocarbons into paraffins is technologically feasible and has been widely studied, there are significant economic incentives to produce olefins. Bimetallic catalysts, in which the metal type and concentration can be used to "tune" catalytic performance, offer considerable promise in this area.The catalytic performance of PtCu/C with Cu/Pt atomic ratios from 0 and 18 and 0.5 percent weight loading Pt in the reaction of 1,2-dichloroethane dechlorination at 200°C and atmospheric pressure was investigated to understand the molecular phenomena governing the change in ethylene selectivity with time on stream (TOS). Chapter 3 examines this transient period by varying catalytic pretreatment. It was theorized that alloy formation, not present after standard pretreatment, results in the formation of ethylene at long TOS.To better understand the molecular phenomena at work in the industrially relevant, carbon-supported catalysts, experiments were undertaken using more homogeneous, silica-supported catalysts. In Chapter 4, a catalytic performance study of a series of these catalysts was undertaken in the dechlorination of 1,2-dichloroethane and complimented by kinetic studies including examination of ethylene hydrogenation and the pulse kinetic behavior of the catalysts in dechlorination as well as a study of chemisorbed CO by FTIR. Large Pt ensembles were found to be present only in catalysts which were ethane selective.Although a significant improvement over carbon-supported systems, silica-supported catalysts with weight loadings of 0.5 percent Pt proved to be too highly dispersed to allow many techniques to be used. To alleviate this concern, a series of catalysts was synthesized with 3.0 weight percent Pt, but these catalysts proved to be highly sensitive to exposure to atmospheric moisture. In Chapter 5, the interactions of these catalysts with water are characterized by examining kinetic performance before and after exposure to water, comparing several types of precursors, and conducting temperature programmed reduction, transmission electron microscopy, and raman spectroscopy. The effect of water was attributed to alleviation of the chromatographic separation of metals which was an artifact of the impregnation procedure.In Chapter 6, the effect of CO on the catalytic performance of the higher weight loading catalysts was studied. Carbon monoxide was found to split large Pt ensembles in much the same manner as alloy with Cu leading to ethylene selectivity in bimetallic catalysts which would otherwise be selective to ethane