Controlling catalytic properties using metal carbides and bimetallic alloys.

摘要

New catalytic materials play significant roles in the discovery and improvement of processes for the environmental protection and chemical production. The conventional development of catalysts relies on time-consuming testing of thousands of catalyst formulations to search for the optimized ones. The main obstacles regarding the discovery of new catalytic materials are the lack of fundamental understanding of the surface properties of the catalysts. In this dissertation, we have taken advantages of surface science techniques to gain an atomic level understanding of the surface structural and chemical properties of potential catalytic materials, and to use it as a guidance to develop novel catalysts for reactions heavily dependent on precious metals.; This work has followed two different routes to achieve the same goal, reducing the usage of Pt-group metals. One method focused on tailoring the surface reactivity of transition metal carbide. The second method explored modified Pt-based bimetallic supported catalysts for hydrogenation processes. Both surface science techniques and fixed-bed flow reactors have been extensively utilized in this study.; The decomposition of NO has been investigated on carbon modified transition metal (W, Mo) model surfaces as well as on tungsten carbide powders. This study has shown that both model surfaces and powder materials are active towards the decomposition of NO into N2. The chemical properties of the metal carbide surfaces are comparable to that of the Pt-group metal surfaces. In addition, surface science studies have demonstrated the structure sensitive feature of the NO decomposition reaction on the well-characterized metal carbide surfaces. Moreover, the feasibility of metal carbide regeneration has been evaluated due to the carbon loss upon the decomposition of NO via the formation of COX.; Inspired by the surface science study on bimetallic surfaces, this work has attempted to transfer these findings from model surfaces to supported catalysts. The Pt-containing bimetallic supported catalysts have exhibited synergistic effects by alloying with second inexpensive metals in a number of hydrogenation reactions. The improved activity and durability have been attributed to the bimetallic alloy formation. This promotion will consequently reduce the utilization of the expensive Pt-group metals and enhance the process profitability.