Reduced graphene oxide as an effective promoter to the layered manganese oxide-supported Ag catalysts for the oxidation of ethyl acetate and carbon monoxide

Abstract

The layered manganese oxide (δ-MnO2)-supported reduced graphene oxide (rGO)-promoted silver catalysts (xAg− yrGO/δ-MnO2; x and y are the Ag and rGO contents (wt%), respectively) were prepared via a polyvinyl alcohol-protected reduction route. Physicochemical properties of these materials were determined using the numerous techniques, and their catalytic activities were evaluated for the oxidation of CO and ethyl acetate. It is found that the loading of rGO as an electron transfer promoter could significantly strengthen the metal−support interaction (SMSI) between Ag and δ-MnO2 and increase specific surface area of the sample, hence improving catalytic performance of the sample. Activity evaluation reveals that 1Ag− 1.0rGO/δ-MnO2 showed the best catalytic activity and the lowest apparent activation energy (Ea), giving a T90% of 140 °C and an Ea of 42.7 kJ/mol for CO oxidation, and a T90% of 160 °C and an Ea of 39.8 kJ/mol for ethyl acetate oxidation at space velocity (SV) = 60,000 mL/(g h). The good performance of 1Ag− 1.0rGO/δ-MnO2 was associated with its high Mn3+/Mn4+ or Oads/Olatt molar ratio, good low-temperature reducibility, and strong SMSI between Ag and δ-MnO2. The in situ DRIFTS characterization demonstrates that the carbonate and acetate species were the main intermediate products in CO and ethyl acetate oxidation over 1Ag− 1.0rGO/δ-MnO2, respectively. The 1Ag− 1.0rGO/δ-MnO2 sample was not significantly altered in physicochemical property after 55 h of stability test, but its activity decreased in the presence of water vapor, especially such an effect on ethyl acetate oxidation was more obvious, which was possibly due to the competitive adsorption of water and reactants on the catalyst surface.