Synthesis and Characterization of New Oxide Hydrates Hx(VxMo1−x)O3·0.3H2O and H0.27(V0.27W0.73)O3·1/3H2O

Glycerol oxidehydration to acrylic acid on complex mixed-metal oxides

“…In both cases, exhaustive characterizations were carried out so as to assess the physical-chemical features of the W-V oxides obtained; as far as their structure is concerned, XRD patterns clearly indicated that the V-containing oxides are isostructural with h-WO x . In particular, the slight decrease in the cell parameters was attributed to the replacement of for the existence of extra-framework protons was clearly provided by TG-analysis [66,74]; indeed, water loss between around 100°C and 500°C exceeded the amount of crystallization water which was stable in the hydrated form at room temperature (molar ratio H 2 O/(W+V)= 0.33). Therefore it was assumed that some of the hydrogen ions in the channels and oxygen atoms from the oxide combined together to form the additional water detected.…”

“…It has been demonstrated that tungsten atoms belonging to the hexagonal framework can be (partially) replaced by other elements such as vanadium, molybdenum, and niobium [66][67][68][69].…”

“…<5 m 2 /g). Only starting from the 1980s have these issues been partially overcome with new "soft" chemical methods (chimie douce) that have paved the way for the synthesis of metastable compounds with high phase purity and significant surface area [66,70]; however, up to the present time, rational design (rather than serendipity) is still a great challenge even for soft methods such as the most common hydrothermal synthesis [71], making the preparation of substituted HTBs (i.e. metastable phases) not so straightforward in the end.…”

“…In order to do so, tungsten-atoms belonging to the oxide lattice can be partially substituted with different transition metals; given the well-known properties of vanadium in oxidation catalysis, the insertion of the latter element is an interesting option. In literature, the substitution of vanadium in the HTB structure has been reported on in recent decades, synthesized both through solid-state and precipitation methods [66,67,74]. In both cases, exhaustive characterizations were carried out so as to assess the physical-chemical features of the W-V oxides obtained; as far as their structure is concerned, XRD patterns clearly indicated that the V-containing oxides are isostructural with h-WO x .…”

“…More likely, an important role is played by contaminants such as Na + ions, which are always present when typical lab-glassware is used and also as impurities in starting materials (W-and V-salts). In fact, in one case, particular precautions were taken to avoid these contaminations [66,74], whereas a more common synthetic procedure was used for the [42][43][44], is good evidence that Brnsted acid sites are predominant in HTBs. In the results and discussion section, for W-Mo-V samples with HTB-structure it will also be reported a study on the presence of Brnsted and Lewis acid sites.…”