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Abstract: In this paper, we report the results of a study on the hydrogenation of hydrocinnamaldehyde (CA) carried out in ethanol under mild conditions (T =333K, ), on the Au/TiO2 reference catalyst, supplied by the World Gold Council. The reaction was carried out on the as received and on the catalyst reduced at 473K (LTR) and 773K (HTR). From the hydrogenation of cinnamaldehyde three main products were obtained: cinnamylalcohol (UA) and hydrocinnamaldehyde (HCA), formed from the hydrogenation of the conjugated Ce:glyph name="dbnd" />O bond, respectively, and the asymmetric ether 3-ethoxyprop-1-enylbenzene (C6H5CH;CH2–O–C2H5) or cinnamyl ethyl ether (CEE). The behavior of Au/TiO2 catalyst in the hydrogenation of cinnamaldehyde is of particular interest because it is the first time, as far as we know, that the formation of the allyl ether is observed during this reaction. The selectivity towards the formation of the CEE, measured at 50% of conversion, increases from 19%, on the as received catalysts, up to 33% on the catalysts reduced at 473K. A further increase of the reduction temperature does not influence the selectivity to CEE. The mechanism of the formation of the cinnamyl ethyl ether is proposed. [Copyright &y& Elsevier]

Following four different procedures many vanadium-based catalysts have been prepared by using the grafting technique and have been tested on the oxidative dehydrogenation of isobutane. The best results of selectivity have been obtained with catalysts prepared by grafting bimetallic vanadium–titanium alkoxides directly on silica. The alkoxide precursors have been obtained by partially hydrolysing titanium alkoxide, dissolved in isopropanol, with a stoichiometric amount of water and reacting then with vanadyl tri-isopropoxide, or alternatively by mixing the two mentioned alkoxides in isopropanol and submitting both to controlled partial hydrolysis. The bimetallic alkoxide grafted on silica show a prevalence of isolated V&z.sbnd;O&z.sbnd;Ti bonds with respect to polyvanadylic V&z.sbnd;O&z.sbnd;V bonds that are prevalent, on the contrary, when vanadyl tri-isopropoxide dissolved in n-hexane is grafted on a TiO2&z.sbnd;SiO2 support. Catalysts characterised by the prevalence of V&z.sbnd;O&z.sbnd;Ti bonds are slightly less active but two times more selective than catalysts in which V&z.sbnd;O&z.sbnd;V bonds prevail. The preparation of vanadium-based catalysts with a favourable TiO2 environment has been largely simplified by avoiding the use of a TiO2&z.sbnd;SiO2 support obtaining, in the meantime, a remarkable improvement in the selectivity. [Copyright &y& Elsevier]

The oxidative dehydrogenation (ODH) of isobutane has been investigated on Ca-doped chromium oxide catalysts supported on γ-Al2O3. The effect of Ca loading on the micro-structural properties of chromia catalysts was investigated by chemical analysis, X-ray diffraction (XRD), scanning electron microscopy with elemental mapping (SEM-EDX), UV-Vis diffuse reflectance spectroscopy (DRS), temperature programmed reduction (TPR), and micro-calorimetry of adsorbed NH3. Cr3+ and Cr6+ species dispersed on alumina, as well as α-Cr2O3 and CaCrO4 crystallites, were found on the catalysts surface. The relative amount of the chromium species depends on the Ca loading. The Cr3+/Cr6+ ratio decreases on increasing the Ca loading due to the preferred formation of bulk chromate species. The Ca loading affects the reducibility of the Cr6+ species and the acid sites strength distribution of the catalysts.The catalytic activity in the ODH reaction of isobutane is enhanced in the presence of amounts of calcium <2 wt.%, then it decreases with a further increase in the Ca content. The selectivity to isobutene follows the same trend showing a maximum (57% at 7% isobutane conversion) on the sample promoted with 2 wt.% of calcium. The reported data suggest that the activity and selectivity to isobutene are due to well-dispersed Cr6+ species on the alumina surface, whereas bulk chromates are less active and give mainly COx. On the basis of micro-structural and catalytic results we proposed that the alkali promoter plays different roles depending on the Ca/Cr ratio. Besides causing changes in surface acidity, calcium increases the amount of well-dispersed Cr6+ species in the range of low Ca/Cr ratios, enhancing the catalytic properties, whereas, at higher Ca/Cr ratios, it acts as a poison promoting the formation of the less active and selective bulk chromate species. [Copyright &y& Elsevier]