The beneficial effect of the addition of base metal oxides to gold catalysts on reactions relevant to air pollution abatement

The present paper reviews some of our recent studies concerning reactions relevant to air pollution abatement over gold based catalysts. In particular, the following reactions will be discussed: 1. CO oxidation. 2. Total oxidation of hydrocarbons. 3. Reduction of NO. 4. Reduction of N2O. 5. Selective oxidation of CO in an atmosphere of hydrogen, in relation to the development of polymer electrolyte fuel cell technology. 6. Selective oxidation of NH3. Large synergistic effects have been found by combining Au/Al2O3 with a transition metal oxide (TMO) or ceria for all the reactions studied in our laboratory. One of the most efficient gold-based catalysts that we developed is based on alumina-supported combinations of Au, CeOx and Li2O. Our model is that most of the chemistry is taking place at the interface of gold and the partly reducible oxide CeOx. The cocatalyst CeOx can provide the O needed for oxidation reactions. The non-reducible alkali or alkali-earth metal oxide functions as a promoter. It enables the formation of small, highly dispersed and thermally stable gold particles on gamma-Al2O3. As a general conclusion, supported gold catalysts are highly active in both oxidation and reduction reactions. The selectivity can be steered into the desired direction by using the right additive. (C) 2004 Elsevier B.V. All rights reserved.