Bulk and surface properties of highly dispersed VOx/ZrO2, VOx/SiO2 and VOx/TiO2/SiO2 systems and their relevance for propane oxidation

Abstract

Highly dispersed vanadium-doped metal oxides such as VO x /ZrO 2 , VO x /SiO 2 and VO x /TiO 2 /SiO 2 with vanadium contents between 0 and 25 mole% were prepared by special bulk preparation methods (coprecipitation and sol-gel, followed by freeze-drying). Bulk and surface properties of the obtained mixed oxide solid solutions were thoroughly investigated by different analytical methods (Raman and FTIR spectroscopy, TPD, H 2 -TPR, oxygen isotope measurements etc.). Moreover, the catalytic behaviour of the oxides was studied for the example of the oxidative dehydrogenation (ODH) of propane to propylene. Independent of the preparation method, the catalytic behaviour of vanadium-doped ZrO 2 and TiO 2 phases is very similar. Both metal oxide solid solutions are very active in propane ODH whereas the catalytic activity of VO x /SiO 2 is relatively low. On the other hand, the reduction of the catalytic activity is accompanied by an improved selectivity for the formation of propylene. The correlation between the catalytic activity and the acidity of the oxide systems is discussed. Oxidation experiments with 18 O 2 clearly show that the ODH reaction occurs according to the Mars-van Krevelen mechanism. Experimental Sample preparationVanadium-doped metal oxides containing up to 25 mole% VO x were prepared by two different routes.

Oxidative dehydrogenation of propane over low-loaded vanadia catalysts: Impact of the support material on kinetics and selectivity

“…At Vanadium loadings below 2 V nm -2 , Broensted acid sites can be excluded referring to [46] and [19]. In these studies the presence of surface acid sites for V-ZrO 2 and VAl 2 O 3 was investigated.…”

Inorganic Cryogels

“…In their experiments, freezing and freeze-drying of wet gels were used to avoid pore collapse due to the extreme surface tension effects of water removal during atmospheric drying and to retain most of the tiny morphological features of gels in the dried state. As the term "cryogel" is most commonly used in papers on inorganic materials obtained by freeze-drying [4][5][6], it will be used here to be consistent with previous studies in this field. Therefore, the first studies on the synthesis of inorganic cryogels go back to the early 1970s [7][8][9], soon after the discovery of the freeze-drying synthesis of inorganic materials from frozen aqueous solutions by Landsberg and Campbell [10].…”

Application of infrared photoacoustic spectroscopy in catalysis

“…Kemnitz et al have applied FT-IR/PAS for pyridine adsorption [124] for the studies of surface acidity and the nature of acid sites in g-alumina [125], sulfated zirconia [126][127][128][129][130], WO 3 / ZrO 2 catalysts [131], modified zirconium and titanium dioxides [132], highly dispersed vanadium-doped metal oxides [133], chromia materials [134][135][136][137], various MgF 2 catalysts [138][139][140], and aluminium fluorides [141][142][143]. In the case of Vansant and co-workers IR/PAS is mostly a supplementary technique in the studies conducted with: silica and/or silicas surface and silica gel [144][145][146][147][148][149][150][151], MoO x layer on the surface of silica [152], adsorption of VO(acac) 2 or V(acac) 2 on silica and alumina [153][154][155], controlled deposition of iron oxide on the surface of zirconia [156], vanadium oxide deposited on thermally stable mesoporous titania [157].…”

“…The largest number of research papers which include FT-IR/ PAS catalytic investigations belongs two scientific groups chaired by Kemnitz [124][125][126][127][128][129][130][131][132][133][134][135][136][137][138][139][140][141][142][143] and Vansant [25,100,. Kemnitz et al have applied FT-IR/PAS for pyridine adsorption [124] for the studies of surface acidity and the nature of acid sites in g-alumina [125], sulfated zirconia [126][127][128][129][130], WO 3 / ZrO 2 catalysts [131], modified zirconium and titanium dioxides [132], highly dispersed vanadium-doped metal oxides [133], chromia materials [134][135][136][137], various MgF 2 catalysts [138][139][140], and aluminium fluorides [141][142][143].…”