Pd/γ-Al2O3–TiO2catalysts containing various compositions of titania and alumina were prepared by sol–gel and wet-impregnation methods in attempt to study the particle size, nature of phases, morphology and structure of the composite samples. The ethanol oxidation experiments, N2adsorption–desorption,FTIR, XRD and XPS were conducted, and the effects of Al2O3content on the surface area, phase transformation and structural properties of TiO2were investigated. The optimal value of ethanol conversion appeared on Pd/Al(0.05)–Ti and Pd/Al(0.90)–Ti catalysts irrespective of the ethanol oxidation temperature, and we call this as a double peaks phenomenon of catalytic activity. The XRD results reveal that the phase composition and crystallite size of the mixed oxides depend on Al2O3/TiO2ratio and calcination temperature. Al2O3can effectively prevent the agglomeration of TiO2and this can be ascribed to the formation of Al–O–Ti chemical bonds in Al2O3–TiO2crystals. Binding energy and Pd surface concentration of the catalysts were modified apparently, which may also lead to catalyst activity changes.
V-Pd/γ-Al2O3-TiO2 catalysts with different vanadium contents were prepared by a combined sol-gel and impregnation method. X-ray diffraction (XRD), N2 adsorption-desorption (BET), X-ray photoelectron spectroscopy (XPS) and catalytic removal of ethanol, acetaldehyde and nitrogen oxides at low temperature (〈300 ?C) were used to assess the properties of the catalysts. The results showed that the sample with 1wt% vanadium exhibited an excellent catalytic performance for simultaneous removal of ethanol, acetaldehyde and nitrogen oxides. The conversions of ethanol, acetaldehyde and nitrogen oxides at 250 ?C were 100%, 74.4% and 98.7%, respectively. V-Pd/γ-Al2O3-TiO2 catalyst with 1 wt% vanadium showed the largest surface area and higher dispersion of vanadium oxide on the catalyst surface, and possessed a larger mole fraction of V4+ species and unique PdO species on the surface, which can be attributed to the strong synergistic effect among palladium, vanadium and the carriers. The higher activity of V-Pd/γ-Al2O3-TiO2 catalyst is related to the V4+ and Pd2+ species on the surface, which might be favorable for the formation of active sites.
Zhe Li Jing Wang Kai He Xia An Wei Huang Kechang Xie