Bibiana P. Barbero

XPS studies for vanadium pentoxide along the catalytic bed: oxidative dehydrogenation of propane

Abstract In this work, the effect of reaction conditions of oxidative dehydrogenation of propane on V 2 O 5 reducibility along the catalytic bed was studied. Extreme conditions of catalytic test (high temperature, P O 2 / P C 3 H 8 ratio =1) have been used. After the catalytic test, V 2 O 5 original orange color changed along the catalytic bed. Thus, three portions differentiated by their color were picked up separately and analyzed by XRD and XPS. The reduction of V 2 O 5 –V 2 O 3 along the catalytic bed was observed by XRD; while surface reduction from V 5+ to V 3+ was also detected by XPS. Assuming that V 5+ –V 4+ redox couple plays a key role in oxidative dehydrogenation reactions, it is concluded that the choice of reaction conditions is very important in order to avoid an excessive reduction of vanadium ions and obviously, to analyze the results properly.

Vanadium species: Sm-V-O catalytic system for oxidative dehydrogenation of propane

Abstract This work deals with the catalytic behavior of SmVO 4 impregnated with vanadium in the oxidative dehydrogenation of propane. SmVO 4 prepared by the citrate method was impregnated using NH 4 VO 3 as precursor of vanadium species. The vanadium contents have been selected to obtain surface coverages as follows: (a) below the theoretical monolayer; (b) slightly above the theoretical monolayer; and (c) equivalent to the double of the theoretical monolayer. Catalysts were investigated by several physicochemical characterization techniques, i.e. BET specific surface area (SSA), X-ray diffraction (XRD), temperature programmed reduction (TPR), Fourier transform infrared spectroscopy (FT-IR), laser Raman spectroscopy (LRS), and electron paramagnetic resonance (EPR). A slight excess of samarium on SmVO 4 was found and it was responsible for the direct combustion of propane. Part of the vanadium added by impregnation reacted with the excess of samarium towards to the formation of SmVO 4 . Then on the impregnated catalysts, the direct combustion of propane was controlled and higher selectivity to propene at low conversion levels was obtained. At vanadium loading below the theoretical monolayer, surface VO x species were formed. They were easily reducible and the bridging oxygen atoms (VOV) would increase the catalytic activity at low reaction temperature. At vanadium loading above the theoretical monolayer, the appearance of V 2 O 5 crystals was favored. The terminal oxygen atoms (VO) existing in V 2 O 5 cause the consecutive combustion of propene. From the Raman and EPR results on the catalysts before and after the catalytic test, the effect of the reaction on the surface definition of the catalysts can be inferred.

Evaluation and characterization of Sm-V-O catalytic system for propane oxydehydrogenation: Sm2O3-impregnated V2O5 catalysts

Abstract Sm-V-O based catalysts were prepared by impregnating V2O5 with different amounts of Sm2O3. These catalysts and the pure phases of reference (V2O5, Sm2O3, and SmVO4) were characterized by specific surface area measurements by the BET method, X-ray diffraction (XRD), temperature programmed reduction (TPR), laser Raman spectroscopy (LRS), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), transmission electron microscopy (TEM), and adsorption–desorption of CO2. Its catalytic performance was compared by using propane oxidative dehydrogenation reaction. The results of physico-chemical characterization indicated that the system evolves to SmVO4 formation by a reaction in the solid state, producing segregation of this new phase. However, due to the fact that the surface tends to become rich in vanadium, mainly in the V2O5 form, the catalytic behavior of V2O5 impregnated with Sm2O3 is not significantly different from that presented by the pure phase. This surface architecture would be achieved because V2O5 can easily migrate on the surface of other oxides when heated at high temperature. But, in the presence of the reaction atmosphere (propane/oxygen mixture), its migration would occur at lower temperatures.