Catalytic activity and thermal stability of Au-CuO/SiO₂ catalysts for the low temperature oxidation of CO in the presence of propylene and NO

Oxidation catalysts in emissions control systems generally contain Pd/Pt and require exhaust temperatures above 200 °C to operate, but under low-temperature conditions, oxidation of CO and hydrocarbons are challenging. As engine efficiency improves and exhaust temperature decreases, there is an increasing demand for high emissions control performance at low temperatures. Therefore, it becomes imperative to design new catalysts that are active at low operating temperatures. Au-CuO_x catalysts, made through the oxidation of AuCu alloy nanoparticles, have been found to be highly active for the oxidation of CO at low reaction temperatures. The catalytic activity for the conversion of CO using Au-CuO_x/SiO₂ was evaluated under simulated lean exhaust conditions (CO, C₃H₆, NO, H ₂O, O₂ and Ar). It was found that the oxidation of CO over the Au-CuO_x/SiO₂ catalyst was inhibited when C ₃H₆ or NO was introduced into the reaction stream. Interestingly, a physical mixture of Au-CuO_x/SiO₂ and Pt/Al₂O₃ worked in synergy to enhance the oxidation of NO to NO₂ with 90% conversion near 300 °C in the presence of CO. This reactivity is on par with Pt/Al₂O₃ NO oxidation activity in the absence of CO. The Au-CuO_x/SiO₂ catalysts were also found to be thermally stable after being aged up to 700 °C for 10 h. The resistance to particle sintering can be attributed to the CuO_x "anchoring" the Au particles to the silica support.