(28d) Hydrogen Production From Methanol Over Gold Supported on ZnO and CeO2 Nanoshapes

In this work we investigate the active nature of gold clusters supported on ZnO and CeO2 nanoshapes produced by hydrothermal synthesis for the decomposition, oxidation, and steam reforming of methanol. Gold atoms and clusters (<1 nm) were dispersed on the {110} facets of CeO2 nanorods, but only gold nanoparticles (~3 nm) were found on the {100} surfaces of CeO2 nanocubes. Gold nanoparticles (1-2 nm) were observed to bind selectively on the {0001} planes of ZnO nanorods, though it was not determined if sub-nanometer particles were also present. On the basis of methanol TPSR/MS analysis it is proposed that surface oxygen supplied by ZnO is responsible for the low temperature (30-80 °C) production of methyl formate by Au-ZnO. Coupling of methanol to methyl formate intermediate is characteristic of the methanol reactions on gold on either oxide support. The Au-CeO2 nanorod is the most active catalyst from those studied due to its higher number of Au-O active sites. Under steam reforming conditions, both catalysts are better than 95% selective to CO2 at 250 °C, and have apparent activation energies in the range of ~ 110-120 kJ/mol. The water-gas shift reaction is not part of the mechanism for the low-temperature methanol steam reforming. Hence, atomically dispersed gold catalysts are excellent prospects for single-stage conversion of methanol to CO-free hydrogen gas.