‘Shape effects’ in metal oxide supported nanoscale goldcatalysts

Abstract

We report the activity of shape-controlled metal oxide (CeO₂, ZnO and Fe₃O₄) supported gold catalysts for the steam reforming of methanol (SRM) and the water gas shift (WGS) reactions. Metal oxide nanoshapes, prepared by controlled hydrolysis and thermolysis methods, expose different crystal surfaces, and consequently disperse and stabilize gold differently. We observe that similar to gold supported on CeO₂ shapes exposing the {110} and {111} surfaces, gold supported on the oxygen-rich ZnO {0001} and Fe₃O₄ {111} surfaces shows higher activity for the SRM and WGS reactions. While the reaction rates vary among the Au–CeO₂, Au–ZnO and Au–Fe₃O₄ shapes, the apparent activation energies are similar, indicating a common active site. TPR data further indicate that the reaction lightoff coincides with the activation of Au–O–M species on the surface of all three oxide supports evaluated here. Different shapes contain a different number of binding sites for the gold, imparting different overall activity.