Publikace (přehled)

Catalytic conversion of ethanol to acetaldehyde under oxidizing conditions over VOx/ZrO2 catalysts with various surface VOx densities has been investigated. Vanadium complexes anchored on the surface of zirconia oxide support are characterized in detail and their catalytic properties reported. The catalysts were prepared by incipient wetness impregnation from a peroxidic solution of ammonium metavanadate. The texture and crystallinity of the catalysts were investigated by N2 physisorption and XRD analysis. The speciation and redox properties of the vanadium complexes were studied by dispersive Raman spectroscopy and the temperature programmed reduction (TPR) method. The effects of vanadium species distribution and ZrO2 support crystallinity on the catalytic activity in the oxidative dehydrogenation of ethanol to acetaldehyde were analyzed and discussed in a broad context. A comparison of the catalytic results with details of the distribution of vanadium complexes has led to the conclusion that vanadium speciation has a great impact on catalytic behavior and that small oligomeric vanadium complexes dominate in the catalysts with vanadium content slightly above half of monolayer capacity, exhibiting the highest catalytic activity and very high selectivity to acetaldehyde (better than 93%). A comparison of the catalytic behavior of VOx supported on tetragonal and monoclinic ZrO2 phases has not revealed any differences in the activity or selectivity of the ethanol ODH reaction. Long-term catalytic experiments have shown good stability of the catalysts (stable conversion and selectivity for more than 600 h).