Studies on three-way catalysis with supported gold catalysts. Influence of support and water content in feed

Abstract

The potential of gold for the reactions of three-way catalysis was examined by converting a model exhaust consisting of 1.1% CO, 0.1% propene, 0.1% NO, O2 (0.95% - stoichiometric, 0.85% - rich, or 1.05% - lean), and water (10% or none) over catalysts containing 1–2wt-% Au supported on Al2O3, La-Al2O3, TiO2, and CeZrOx supports. For comparison, CO and propene were also reacted stoichiometrically with oxygen in absence of further reactants, likewise, reduction of NO with CO was examined. It was found that propene is a strong poison for CO oxidation, but the intensity of the poisoning effect depended on the support (Al2O3>La-Al2O3>TiO2>CeZrOx). The poisoning was strongest in dry feed but was partly alleviated in moist feed. NO was poorly converted both in the TWC mixture and in binary feed. In the model exhaust, NO conversion resulted in significant N2O formation at low temperatures, but selectivity to N2 increased with temperature. Despite poisoning by propene, Au/CeZrOx outperformed a commercial reference catalyst in CO and propene oxidation. Calcination in moist dilute air at 923K inflicted only moderate damage to the Au catalysts. Over Au/CeZrOx, CO oxidation in stoichiometric feed was not significantly affected at all, but the poisoning effect of propene became more severe in the TWC model feed. Analogous treatment at 1223K resulted in inacceptable damage to all reactions involved and on all supports.