Performance and Stability of the Ru–Re/γ-Al2O3 Catalyst in the Total Oxidation of Propane: Influence of the Order of Impregnation

Abstract

Ru–Re/γ-Al2O3 catalysts were prepared by two sequential impregnation methods and their performances for the total oxidation of propane were investigated. TEM, XRD and H2 chemisorption data showed that the metal particle size was about 1.8 nm on both bimetallic catalysts. However, compared to the Ru/γ-Al2O3 catalyst with dispersion of 0.52, the Ru dispersion was improved by the presence of Re going from 0.64 for the catalyst with Re deposited on Ru/γ-Al2O3, to 0.70 for the sample with Ru deposited on Re/γ-Al2O3. The O2 adsorption data indicated that in the Re-modified catalysts the subsurface oxidation of Ru was suppressed, while in the Ru/γ-Al2O3 catalyst ruthenium was oxidized to a larger extent under oxidizing conditions at room temperature. The Ru deposited on Re/γ-Al2O3 exhibited a catalytic performance slightly better than the catalyst with Re impregnated on Ru/γ-Al2O3, but activity of Re-modified catalysts was not improved as compared to the Ru/γ-Al2O3 catalyst. On the other hand, bimetallic Ru–Re/γ-Al2O3 catalysts present better online stability and no deactivation was observed after the on-line tests for 30 h at temperature of 220 °C. TEM and XRD data showed that oxidized rhenium species strongly interacted with γ-alumina prevented large agglomeration of the Ru phase under O2-rich reaction conditions. The used monometallic Ru catalyst contained RuO2 oxide with crystallite size of 26 nm, while in the used bimetallic catalysts with size of 6–7 nm. Thus, in the consecutive catalytic tests Re-promoted Ru/γ-Al2O3 catalysts present higher activity and extended resistance to deactivation.