Effect of support material on the adsorption structures of furan and maleic anhydride on the surface of V 2O 5/P 2O 5 catalysts : II. Results of In Situ Infrared Spectroscopic Studies

Abstract

The structures of furan and maleic anhydride (MA) adsorbed on surfaces of Al 2O 3-supported and TiO 2-supported V 2O 5/P 2O 5 catalysts (V 2O 5/P 2O 5/support=5/5/90 mass-%) were investigated by IR spectroscopy. For furan four different adsorption structures could be observed at temperatures below 500 K: a cationic allyl complex, that interacted in 2-position with the catalyst, an oxyfuran complex, a 2-(5H)-furanone complex and an aldehyde maleate complex. Between 573 and 648 K adsorbed maleic anhydride and maleate complexes were observed additionally. Aldehyde maleate and maleate were favored on the surface of the Al 2O 3,-supported catalyst. At temperatures below 423 K maleic anhydride interacted with hydroxyl groups of the catalyst surface via hydrogen bonds; a maleate complex as well as a maleic acid complex and an acid maleate complex were identified. Maleate was favored on the Al 2O 3-supported catalyst when furan was adsorbed. Between 427 and 573 K the maleate complex was observed only on the surface of the Al 2O 3-supported catalyst. Ring opening facilitated by hydroxyl groups existing on the Al 2O 3 support is assumed to be responsible for the non-selective oxidation of furan and for the oxidative degradation of MA on the Al 2O 3-supported catalyst. The results have been confirmed by IR spectroscopic investigation of the structures of MA adsorbed on γ-Al 2O 3 and TiO 2 alone. MA adsorption was strongest on γ-Al 2O 3; also the formation of maleate structures were favoured on this support.