CATALYTIC TRANSFORMATION OF ETHANOL OVER MICROPOROUS VANADIUM SILICATE MOLECULAR-SIEVES WITH MEL STRUCTURE (VS-2)

The transformation of ethanol was carried out over vanadium silicate m olecular sieves with MEL topology (VS-2) with different Si/V atomic ra tios in the temperature range 523-623 K. The reaction was performed in a fixed-bed down-flow reactor at atmospheric pressure. Acetaldehyde, diethyl ether, and ethylene were the major products along with small a mounts of acetone, acetic acid, ethyl acetate, and carbon oxides, The conversion increased while the selectivity toward acetaldehyde decreas ed with increase in reaction temperature, The kinetics of the reaction (at 5% conversion) indicated a nearly fist-order dependence of the ra te of formation of the major products on ethanol. The formation of ace taldehyde is suggested to be mainly through the involvement of the van adyl species (V=O) while diethyl ether production is controlled by the simultaneous involvement of V=O and V-O-Si associated with vanadium i n the lattice, The intrinsic activity of vanadium incorporated into th e zeolite framework is nearly 10 times that of the vanadium present in the impregnated sample. The nature of the sites involved in the forma tion of the different products, as elucidated from spectroscopic techn iques (NMR and ESR), and the possible reaction mechanisms are proposed . (C) 1997 Academic Press.