Oxidative dehydrogenation of propane over (Mo)-Sm-V-O catalytic system. Role of the different phases

The (Mo)-Sm-V-O catalytic system has been exhaustively studied in the propane oxidative dehydrogenation reaction. In order to obtain different surface arrangements, simple oxides (V2O5, SM2O3 and MoO3), SMV mixed oxides with different Sm/V molar ratio and SMVO4 impregnated with vanadium, samarium or molybdenum were prepared. The function that the possible arrangements play has been identified. A slight samarium excess favors total combustion causing a strong drop of selectivity, therefore, it is necessary to avoid it. On the other hand, vanadium excess constituting surface vanadium oxide species (VOx) notably increases the catalytic activity while a higher vanadium amount leads to crystalline V2O5 formation and the catalyst behavior tends to that of bulk V2O5, Molybdenum at low concentrations constitutes surface molybdenum oxide species (MoO.) which showed to be highly selective in propane ODH. High contents of molybdenum favor the formation of crystalline MoO3, thus, causing an important catalyst deactivation. Finally, a comparison with other known efficient vanadium based catalysts is made and hence, the potentiality of (Mo)-Sm-V-O catalysts is shown

Solid-state reactivity of iron molybdate artificially contaminated by antimony ions and its relation with catalytic activity in the selective oxidation of isobutene to methacrolein

Catalysts were prepared by impregnation of Fe-2(MoO4)(3) with different quantities of antimony butoxide. BET surface area measurement, XRD, Mossbauer spectroscopy, CTEM-AEM, XPS and ISS were used to characterize phase and surface architectures and their changes after calcination and catalytic reaction. Before calcination, antimony was present as pure oxide or hydroxide, partly as particles and partly as an incomplete monolayer on the surface of Fe-2(MoO4)(3). After calcination at 400 degrees C, antimony got detached from the Fe-2(MoO4)(3) surface and aggregated very intensively, partly as Sb2O4 and partly, through reaction with the iron molybdate, as a mixture of distorted FeSbO4 and MoO3. After reaction or calcination at 500 degrees C, more distorted FeSbO4 and MoO3 are formed, separated from Fe-2(MoO4)(3). Selective oxidation of isobutene to methacrolein was carried out on the calcined material. Impregnated catalysts show considerably improved catalytic performances compared to the pure Fe-2(MoO4)(3) phase or mechanical mixtures of it with alpha-Sb2O4. The catalytic performances are explained by several catalytic cooperations via spillover oxygen. These cooperative effects involve all the oxide phases present in the material having worked as catalyst: Fe-2(MoO4)(3) (pure or possibly contaminated by small amounts of antimony oxide), FeSbO4, MoO3 and SbyOx

Solid-state Reaction in the Iron-molybdenum-antimony Oxide System

This work deals with the evolution of a mechanical mixture of Fe2(MoO4)3 and alpha-Sb2O4 (prepared separately) during calcination in air at 500-degrees-C over a period of six days. The samples were studied by X-ray diffraction, X-ray photoelectron spectroscopy, BET surface area, CTEM, analytical electron microscopy and selected area electron diffraction. A reaction occurs between the two phases, leading to a mixture of Fe2 (MoO4)3, Sb2O4, FeSbO4 and MoO3 with a significant increase of the surface area. Taking into account previous results, the present work suggests that the ability of alpha-Sb2O4 to produce oxygen spillover facilitates the oxidation of Sb3+ to Sb5+ allowing the solid state transformation to FeSbO4 to take place