Abstract
Lean-burn engine technology offers improved fuel economy; however, the reduction of NOx during lean-operation continues to be a major technical hurdle in the implementation of energy efficient technology. Recently reported passive NH3-SCR system (PASS)– a simple, low-cost, and urea-free system – has the potential to enable the implementation of lean-burn gasoline engines; however, the system suffers from CO slips during extended rich operations. The slipped CO can be easily oxidized with supplemental oxygen feed over platinum group metal (PGM)-based catalysts; however the PGM-based catalysts simultaneously oxidize the generated NH3. This work focuses on the preparation of catalysts that can preferentially oxidize CO in the presence of NH3.Highly active bimetallic Au-Ru/Al2O3 catalysts were prepared by the method of [AuCl4]− reduction by hydrogen preadsorbed on a parent monometallic Ru/Al2O3 catalyst serving as a carrier. The temperature-programmed reduction studies confirmed a strong interaction between the Au and Ru particles in the samples prepared by this redox method. The average size of crystallites was less than 7nm and 20nm for Au and Ru, respectively. The activity of the catalysts was studied in the reaction of oxidation of a mixture of CO with NH3. The catalytic activity in CO oxidation was found to be higher over the bimetallic Au-Ru/Al2O3 catalyst compared to the monometallic Ru/Al2O3 and Au/Al2O3 catalysts. On the contrary, in NH3 oxidation, the bimetallic Au-Ru/Al2O3 catalyst exhibited a decreased activity compared to the relevant monometallic catalysts. Preparation of Au-Ru/Al2O3 samples by the commonly used method of deposition-precipitation with urea resulted in the less catalytically active samples due to the formation of larger Au particles and their separate deposition from Ru.
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