(488d) First-Principles Study of Methanol Steam Reforming On Cobalt and Cobalt Oxide Surfaces
Steam reforming of bio-derived alcohols or dimethyl ether for the production of hydrogen is a potential substitute to fossil fuels for both energy storage and automotive fuel. Co-based catalysts have been shown to be promising catalysts for ethanol steam reforming, but there is still much debate about the nature of the active site, the role of the oxide support, and reaction mechanisms. In operando XAFS studies indicate a mixture of cobalt metal and oxide phases under reaction conditions but the exact role of the two phases is still not clear. We will report density functional theory (DFT) based studies of methanol steam reforming (MSR) on both the metallic Co and Co oxide surfaces. The MSR reaction is chosen since it provides a simpler set of reaction pathways to explore than ethanol or butanol. We examined the adsorption of reactants, products, and intermediates that are along the MSR reaction pathways suggested by previous studies. For each species we determined the most stable structure and based on this information we have constructed a free energy diagram for the reaction pathways for reforming methanol on Co(0001) surface. We have also used the nudged elastic band (NEB) method to determine the transition states and energy barriers for important elementary steps to study the kinetics, especially for the competing steps that effect product selectivity. We will discuss the implications of our calculations to experimental results and other DFT studies of MSR on other metal surfaces. We will also present on going studies of the same reaction steps for MSR on CoO(100) and CoO(111) surfaces.