Vanadium Phosphorus Oxide Catalyst Modified by Niobium Doping for Mild Oxidation of n-Butane to Maleic Anhydride

• DOI: 10.1006/jcat.2002.3562
• Publication Date: 2002-10-06T18:14:43Z
• Authors: Andréa M. Duarte ...; Wilma de A. Gonzalez; Paulo G. Pries de...; Jean-Guillaume Eon; Jean-Marie Herrmann; Mimoun Aouine; Stéphane Loridant; Jean-Claude Volta
• Keywords: Butane; Maleic anhydride; Niobium oxide

Abstract The interest of doping (VO) 2 P 2 O 7 with Nb 5+ ions has been studied for n -butane oxidation to maleic anhydride. Nb was solubilized as niobium (V) ethoxide into isobutanol and used as a reducing reagent to prepare the VOHPO 4 ·0.5H 2 O precursor. Under n -butane fuel-lean oxidation conditions, the VNbPO precursor was activated at a temperature 20°C lower than for undoped VPO because of a modification of its morphology. Electron microscopy showed that the activated VNbPO catalyst is more disorganized than the activated VPO. It contains more defects and concentrates Nb at the surface. Nb acts as an n -type dopant for the p -type (VO) 2 P 2 O 7 semiconductor, as observed in electrical conductivity measurements. 31 P NMR by spin-echo mapping and XPS spectroscopy provide evidence that the VNbPO catalyst is more oxidized, particularly at the surface. Doping with Nb creates defects, responsible for C–H n -butane activation, which have been observed to be associated with Lewis acid sites of low acidity. This is the reason for the enhancement of the n -butane conversion. Selectivity to maleic anhydride is not modified by Nb-doping while CO 2 /CO formation is increased due to the higher surface V 5+ /V 4+ ratio.