Oxidation of butane and butadiene to furan over vanadia–silica mixed oxides

Abstract

Vanadia–silica mixed oxides (aerogels and xerogels), derived from the sol–gel preparation route, were tested in the partial oxidation of n-butane and 1,3-butadiene to furan. The dependence of the furan selectivity on morphological properties and vanadium dispersion in the silica matrix has been studied. The catalysts were characterized by N 2 and Ar physisorption, AAS, XPS and FTIR spectroscopy. Surface acidic centers of the materials were assessed by means of DRIFT-measurements of adsorbed NH 3 probe molecules. The structural properties, mainly influenced by the drying procedure of the sol–gel samples, had a major influence on the catalytic performance of the sol–gel materials. Aerogels were the most selective catalyst, converting butane to furan with only 3% selectivity. The maximum furan selectivity in butadiene transformation was about 25%, but considerable coke formation was also observed. Microporosity, found in conventionally dried sol–gel materials seems to be unfavorable for furan selectivity. The presence of Brønsted acidic sites was proved to be necessary for furan formation. Studies involving V 2O 5, SiO 2, and vanadia–silica low-temperature aerogels with 5–20% vanadia contents revealed that the selectivity to furan was diminished by silica due to its intrinsic high activity for total oxidation and cracking. A comparison to literature data indicated that vanadia–silica mixed oxides and vanadia grafted on silica are markedly less selective towards furan than VPO catalysts.