Methanol Steam Reforming Over Gold Supported On ZnO Nanoshapes

In this study we investigate the active nature of nano-scaled gold supported on ZnO ‘nano-shapes' for the steam reforming of methanol (SRM). By utilizing a hydrothermal growth route, we were able to control the fraction of exposed {0001} surfaces on ZnO nanostructers. When gold was added by the deposition-precipitation (DP) method, gold nanoparticles (~1-2 nm) were observed (by TEM) to bind selectively on the {0001} planes of ZnO nanorods; however, it was not determined if sub-nanometer particles were also present. When gold was deposited by colloidal techniques, it appeared (by TEM) that there was no preference in binding sites of gold particles (~1-3 nm); we propose this effect is due to PVP encapsulation prior to heat treatment. On the basis of TPSR/MS analysis we demonstrate that gold added by DP shows higher activity for SRM over Au-ZnO nanorods (1.1 compared to 3.6 μmol/g/s at 250°C). Furthermore, Au deposited on ZnO nanostrucutres with the highest fraction of exposed {0001} surfaces shows the highest activity for SRM. We propose that active gold species bind in naturally occurring oxygen and zinc vacancies in the lattice of polar ZnO surfaces. Active Au-ZnO samples (polyhedral and short rods) are better than 95% selective to CO2 under 250 °C. In addition, the presentation will include sample characterization, kinetic and mechanistic information.