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

摘要

Ru-Re/gamma-Al2O3 catalysts were prepared by two sequential impregnation methods and their performances for the total oxidation of propane were investigated. TEM, XRD and H-2 chemisorption data showed that the metal particle size was about 1.8 nm on both bimetallic catalysts. However, compared to the Ru/gamma-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/gamma-Al2O3, to 0.70 for the sample with Ru deposited on Re/gamma-Al2O3. The O-2 adsorption data indicated that in the Re-modified catalysts the subsurface oxidation of Ru was suppressed, while in the Ru/gamma-Al2O3 catalyst ruthenium was oxidized to a larger extent under oxidizing conditions at room temperature. The Ru deposited on Re/gamma-Al2O3 exhibited a catalytic performance slightly better than the catalyst with Re impregnated on Ru/gamma-Al2O3, but activity of Re-modified catalysts was not improved as compared to the Ru/gamma-Al2O3 catalyst. On the other hand, bimetallic Ru-Re/gamma-Al2O3 catalysts present better online stability and no deactivation was observed after the on-line tests for 30 h at temperature of 220 degrees C. TEM and XRD data showed that oxidized rhenium species strongly interacted with gamma-alumina prevented large agglomeration of the Ru phase under O-2-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/gamma-Al2O3 catalysts present higher activity and extended resistance to deactivation.