Methane Reforming on Single Atom Catalysts

Abstract

Heterogenous catalysis is a key process in chemical conversion and energy application. The catalytic performance is determined by the structure and properties of catalytic active sites under working conditions, which are difficult to be characterized by conventional techniques. Studies of structure of a catalyst at atomic level could help to build up correlation between the catalyst structure and its corresponding catalytic performance. Then, new catalyst with better performance and long-life time could be rationally designed. In-situ/operando techniques, such as near ambient XPS, in-situ XAS and Environmental TEM, have been developed and discussed in Chapter 2 to resolve the structure and chemical state of the active sites during catalysis condition. Methane has been an inexpensive source to provide fuels and chemicals in recent decades. It attracted much attention to catalytically convert methane to high value intermediate and chemical products. A major challenge is, how to design a catalyst which could activate C-H bond of methane effectively to from ideal intermediate compound for chemical industries. In the research work of dissertation catalysts containing singly dispersed transition metals on oxide support were designed. They effectively convert methane to syngas. Methane reforming with water and CO2 can readily be catalyzed over Rh1/CeO2 catalyst, with a significantly lowered activation energy barrier compared to Rh nanoparticles supported on CeO2. In-situ XAS and NAP-XPS reveals chemical state of Rh1/CeO2 catalyst. Moreover, a catalyst containing two sets of singly dispersed single metal atoms, (Ni1+Ru1)/CeO2 was designed for methane reforming. The synergistic effect on catalytic activity between the two sets of metal cations were exhibited. Computational studies suggest that the synergistic effect is originated at that (1) the different role of Ni1 and Ru1in terms of activations of CH4to form CO on Ni1 site and dissociation of CO2 to CO on Ru1 site, respectively, and at (2) the sequential role in terms of first forming H atoms through activation of CH4 on Ni1 site and then coupling H atoms to formH2 on Ru1 site.