Amorphous aluminium fluoride as new matrix for vanadium-containing catalysts

Abstract

A new sol–gel technique was developed for preparing vanadium-containing aluminium fluoride catalysts for selective oxidation reactions. With this new synthesis, highly dispersed vanadium species can be obtained in the metal fluoride host lattice. The X-ray amorphous solids were investigated by conventional and advanced analytical methods such as for instance N₂ adsorption experiments, FTIR spectroscopy, pyridine adsorption and NH₃-TPD. The surface properties, acidity and catalytic performance were all dependent on the vanadium content of the samples. EDX, FTIR and Raman spectroscopy confirmed the high degree of dispersion of vanadium (oxidation state: III or IV or both) species in the aluminium fluoride matrix. The samples had relatively high BET surface areas and medium strength Lewis acid sites. Additional Brønsted acid sites were observed on samples with higher vanadium contents only. The catalytic performance of the vanadium-containing aluminium fluorides was investigated for the oxidative dehydrogenation (ODH) of propane. Depending on the vanadium content, the new catalyst system offers a surprisingly high catalytic activity and selectivity towards the desired product, propylene. The high degree of dispersion of the active vanadium species in the aluminium fluoride matrix and the type of the acid sites on the solid surface are crucial to the selectivity of the catalyst in the selective oxidation reaction.