ZnO-modified zirconia as gold catalyst support for the low-temperature methanol steam reforming reaction

Abstract

Nanoscale zirconia (ZrO2) is widely investigated both as catalyst support and catalyst. Bare ZrO2 binds gold weakly due to lack of surface defects. In this study, nanoscale ZrO2 was modified with zinc oxide (ZnO) at different amounts, and examined as support of gold catalysts for the methanol steam reforming (SRM) reaction. ZrO2 with high specific surface area serves as dispersant of ZnO to create highly dispersed ZnO clusters, which provide more anchoring sites for strong gold-metal oxide bonding. Addition of ZnO also passivates the surface acidity of ZrO2, thus blocking the direct methanol decomposition to CO and H2. To prepare the highly dispersed ZnO clusters on ZrO2, a carbon hard-template method was used, followed by calcination at 550°C to produce a highly porous mixed oxide solid. To investigate the modification of ZrO2 by ZnO, the surface acidity was probed with isopropanol in temperature-programmed desorption (TPD) mode. Adsorption of the gold precursor on the ZnO-modified ZrO2 was carried out by the anion adsorption method. Better dispersion, and better activity and stability of these gold catalysts were found than on either pure ZrO2 or ZnO. Accordingly, the light-off temperature of SRM is lower and a wider temperature window for CO-free H2 production up to moderately high temperatures (∼375°C) is found.