No abstract

No abstract

VO x /SBA-15 catalysts with five different vanadium loadings were prepared by a modified wet impregnation method, characterized using N 2 adsorption, XRD, EDX, SEM, Raman and UV-vis spectroscopies and H 2 -TPR techniques, and tested in the oxidative dehydrogenation of propane in the temperature range 450-600 • C. For all the catalysts the propane conversion increases with both reaction temperature and vanadium loading, while the selectivity for propene decreases mainly to the benefit of carbon oxides. Several types of VO x species coexist on the catalyst surface, with monomeric and low-polymerized ones leading mainly to propene, while V 2 O 5 crystallites at high vanadium loadings producing more carbon oxides. Propene was determined to be the only primary product irrespective of the vanadium content.

No abstract

No abstract

No abstract

Copper ferrites dopped with molybdenum were studied in an oxidative coupling reaction between methanol and ethanol in the gas phase. The catalysts have been characterized by X-ray diffraction, where the presence of ferrite, magnetite, and tenorite phases was observed; scanning electron microscopy; UV-Vis spectroscopy; and Fourier-transform infrared spectroscopy, which highlighted the presence of octahedral coordination of isolated molybdena species. The catalyst with the highest activity in this reaction and with the highest selectivity to hydroxyacetone is the one that presents Lewis sites with weak acidity. The methyl and ethyl acetate selectivities are directly proportional to the Cu/Fe ratio. It has been observed that the presence of reduced copper sites is responsible for the selectivity in esters, while the presence of reduced iron and molybdenum sites is responsible for the acetol production.

Esterification of acetic acid with n-Butanol has been studied in a heterogeneous reaction system using two g-alumina-supported vanadium oxide catalysts with different V loadings, which were prepared by the impregnation of a precipitated alumina. The alumina support and the supported catalysts were characterized using X-ray diffraction, N 2 adsorption, EDX analysis and NH 3 -TPD techniques. The effects of the reaction time, of the molar ratio of the reactants, of the speed of agitation and of the mass fraction of the catalyst on the catalytic properties were studied. In the presence of the supported catalyst containing 10 wt % V 2 O 5 (10V-Al 2 O 3 sample) the conversion reached 87.7% after 210 min of reaction at 100 8C with an n-Butanol-to-acetic acid mole ratio equal to one. The conversion as well as the total acidity measured by TPD of NH 3 increased in the following order: Al 2 O 3 < 5V-Al 2 O 3 (5 wt % V 2 O 5 /Al 2 O 3 ) < 10V-Al 2 O 3 . In all cases the reaction was completely selective to n-butyl acetate. Nevertheless, a loss in catalytic activity after three reaction cycles with 10 V 2 O 5 -Al 2 O 3 catalyst was observed.