‘Shape effects’ in metal oxide supported nanoscale gold catalysts

Abstract

We report the activity of shape-controlled metal oxide (CeO(2), ZnO and Fe(3)O(4)) 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 CeO(2) shapes exposing the {110} and {111} surfaces, gold supported on the oxygen-rich ZnO {0001} and Fe(3)O(4) {111} surfaces shows higher activity for the SRM and WGS reactions. While the reaction rates vary among the Au-CeO(2), Au-ZnO and Au-Fe(3)O(4) 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.

The Use of C-MnO2 as Hybrid Precursor Support for a Pt/C-MnxO1+x Catalyst with Enhanced Activity for the Methanol Oxidation Reaction (MOR)

“…This has been extensively reported for PtRu catalysts [18,20,21]. In the case of Pt-transition metal oxide based catalysts this effect can also be observed [14]. In particular, for our Pt/C-MnxO1+x catalyst, the onset potential is 70 mV lower than for the commercial Pt/C catalyst.…”

“…It is also known that the interaction between metal crystallites and an oxide surface is influenced by the nature of interfacial contact and the crystalline characteristic of the oxide. MnO2 with smaller and uniform crystalline orientation as well as suitable surface morphology should offer apposite active sites for facile interaction with Pt crystallites, which can provide optimized synergistic effect for alcohol electro-oxidation [14]. However, the effect of microstructure/morphology of manganese oxides on the nature of Pt dispersion on MnxO1+x/carbon-based electrocatalysts has not been extensively investigated so far [10].…”

Effect of Microgravity on Synthesis of Nano Ceria

“…This was attributed to the generation of oxygen vacancies of ceria [32]. Flytzani-Stephanopoulos and colleagues synthesized nano-polyhedra, rods and cubic ceria particles using hydrolysis method and examined its catalytic activity for various reactions [19,[34][35][36][37]. They demonstrated that different shapes of ceria nanoparticles exposing different crystal planes on the catalyst surface significantly influenced the Au dispersion on the ceria support.…”

Review: monoclinic zirconia, its surface sites and their interaction with carbon monoxide

“…aberration-corrected TEM as in 94 ) to determine the orientation of the exposed surfaces. Boucher et al 95 have tested different shapes of metal oxides with gold catalysts for steam reforming of methanol and water-gas shift, and they conclude that the different shapes show somewhat different activities. Li and Shen 96 discuss widely the oxide shape effects in nanocatalysis, and they mention some of the unknown issues with metal deposition on oxide nanoshapes: whether the metal atoms are located on a single type of surface only.…”