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

Abstract

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–CuOx 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–CuOx/SiO2 was evaluated under simulated lean exhaust conditions (CO, C3H6, NO, H2O, O2 and Ar). It was found that the oxidation of CO over the Au–CuOx/SiO2 catalyst was inhibited when C3H6 or NO was introduced into the reaction stream. Interestingly, a physical mixture of Au–CuOx/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–CuOx/SiO2 catalysts were also found to be thermally stable after being aged up to 700°C for 10h. The resistance to particle sintering can be attributed to the CuOx “anchoring” the Au particles to the silica support.