Monique Rigole

Effect of the sequence of potassium introduction to V2O5/TiO2 catalysts on their physicochemical properties and catalytic performance in oxidative dehydrogenation of propane

Abstract Two series of K-promoted V 2 O 5 /TiO 2 catalysts were prepared by: (a) deposition of vanadia on K-doped TiO 2 support (TiK V preparations), and (b) deposition of K on vanadia-titania catalysts (TiV K preparation). They were characterized by 51 V NMR, XPS, surface potential (work function) techniques and isopropanol decomposition, a probe reaction for the acid-base properties, and tested in oxidative dehydrogenation of propane (ODH). It has been found that the sequence of the K introduction in the preparation step is preserved in the calcined preparations, with more potassium being present on the surface of TiV K than TiK V catalysts. The vanadium species on TiK V samples include V 2 O 5 and polymeric [VO x ] γ species. The TiV K sequence leads to the formation of potassium vanadates (KV 3 O 8 and possibly KVO 3 ), and to the decrease in the amount of V 2 O 5 . The TiV K catalysts are more active and selective in the ODH of propane, and more active in isopropanol dehydrogenation to the acetone (thus more basic) than the TiK V samples.

Effect of potassium addition to the TiO2 support on the structure of V2O5/TiO2 and its catalytic properties in the oxidative dehydrogenation of propane

Vanadium oxide has been deposited by a grafting technique onto TiO2 anatase, both pure and doped with potassium [(1.2 and 2.5) atoms nm–2]. The V content varied between 0.1 and 20 atoms nm–2[0.01–2 V2O5 monolayers (ML)]. The prepared samples were characterized by X-ray photoelectron spectroscopy (XPS), 51V magic-angle spinning (MAS) NMR and a surface potential (SP) technique and tested as catalysts in the oxidative dehydrogenation (ODH) of propane and propan-2-ol decomposition, a probe reaction for acid–base properties. From the XPS and SP data it has been inferred that VOx are located beside the K centres on the bare surface of TiO2 with the lower K content sample, whereas they cover the K-doped fraction of the surface for the sample with higher K content. Monomeric and polymeric VOx species and V2O5 were detected by 51V NMR on pure and K-doped catalysts. For the K-doped samples the polymeric species were observed only at high V content and new tetrahedral VOx species and traces of KVO3 appeared. It has been found that the presence of K on the TiO2 surface leads to (a) a decrease in the reducibility of the vanadia phase at low V content; (b) a decrease in the surface potential (electronic work function); (c) a decrease in acidity and increase in basicity and (d) a decrease in the total activity for ODH of propane. The pattern of the activity and selectivity changes with the total V content depends on the amount of K on the support surface: with K 1 ML) are required to obtain the same catalytic performance. Polymeric [VOx] species seem to be more active and selective in the ODH of propane than monomeric species or bulk V2O5.

Oxidative dehydrogenation of isobutyric acid on H4PVMo11O40, NaxH4-xPVMo11O40 and CUyH4-2yPVMo11O40 heteropolyacid catalysts supported on silica

Abstract The oxidative dehydrogenation of isobutyric acid (IBA) to methacrylic acid (MAA) was studied over the heteropolyacid H4VMo11O40 and the acidic salts NaxH4-xPVMo11O40 and CuyH4-2yPVMo11O4. supported on silica, as catalysts. The presence of copper as counter-cations in the heteropoly compounds increases the activity and the selectivity to MAA. This increase is probably due to the simultaneous presence in the solids of Bronsted acidity and oxygen vacancies with an adequate ratio. These latter sites can more easily be obtained in the presence of Cu2+ and V4+ than with Na+ counter-ions in the catalysts.

Synthesis of high surface area boria–alumina mixed oxides characterization by 11B- and 27Al-NMR

Abstract Boria–alumina mixed oxides were synthesized by the sol-gel method. MAS-NMR spectroscopy spectra exhibited two boron species, BO 3 and BO 4 , the former giving an important second order quadrupolar effect. Then, spectra were interpreted with a simulation software which permitted quantitative evaluation of boron species in both dried and calcined states. Tetrahedral Al species formed in the dried state appear to monitor BO 4 and BO 3 species formation in both dried and calcined states.