The effects of stepped sites and ruthenium adatom decoration on methanol dehydrogenation over platinum-based catalyst surfaces

A density functional theory study of methanol dehydrogenation over stepped Pt(2 1 1) surfaces without and with Ru modification was carried out to understand fuel catalytic reactions on Pt-based catalysts. Two main pathways of the CH3OH dehydrogenation were examined: the O–H pathway which was initiated by O–H bond scission to form the methoxy (CH3O) intermediate followed by sequential cleavage of C–H bonds to CO, and the C–H pathway which was initiated by C–H bond scission to form the hydroxymethyl (CH2OH) followed by two C–H bond cleavages to COH and then CO. Possible crossover reactions between the O–H and C–H pathways were also computed. Compared to flat Pt(1 1 1), stepped Pt(2 1 1) increases the adsorption energies of intermediates, making no significant contribution to decreasing the reaction barriers of most elementary steps involved, except in the first hydrogen scission. However, on the Ru-modified surface, a significant reduction was found in reaction barriers for the first step of the C–H bond scission and a number of further dehydrogenation steps crossing over to the O–H pathway, with the most facile paths identified. Our data reveals the complexity of methanol catalytic reaction processes at the atomic level and contributes to a fundamental understanding of fuel reactions on Pt-based catalysts.

Activity Enhancement of Tetrahexahedral Pd Nanocrystals by Bi Decoration towards Ethanol Electrooxidation in Alkaline Media

Tetrahexahedral Pd nanocrystals (THH Pd NCs) were prepared on a glassy carbon electrode using a programmed square-wave potential electrodeposition method, and modified by Bi adatoms with a range of coverages via the cyclic voltammetry method. The reactivity of the catalysts prepared towards ethanol electrooxidation reaction (EOR) was studied in alkaline medium at various temperatures and under other conditions that practical fuel cells operate. Significant activity enhancements were observed for the Bi-modified THH Pd NCs with an optimum Bi coverage (θBi) of around 0.68 being obtained. Furthermore, it was found that increasing temperature from 25 ºC to 60 ºC enhances the reactivity significantly. The general kinetics data of EOR on Bi-decorated and bare THH Pd NCs have also been obtained, from the activation energy calculated based on Arrhenius plots, and compared. At the optimum Bi coverage, an enhancement in the activity of almost 3 times was achieved, and the corresponding activation energy was found to be reduced significantly.