Preparation of alumina-supported gold-ruthenium bimetallic catalysts by redox reactions and their activity in preferential CO oxidation
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 7 nm and 20 nm 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.
Graphical abstract.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Au0 nanoparticles were redox deposited on alumina-supported Ru0 nanoparticles. ► Au/Ru/θ-Al2O3 catalysts are more active in CO oxidation than Au/θ-Al2O3 and RuO2/θ-Al2O3; Au0–Ru0 interaction suppresses the NH3 oxidation.
Journal: Applied Catalysis B: Environmental - Volumes 134–135, 2 May 2013, Pages 123–129