Mechanochemistry: the activation method of VPO catalysts for n-butane partial oxidation

Abstract

The paper describes the influence of the introduction of alkali and alkaline-earth metals into the VPO precursor and the effect of bismuth additive introduced into the VPO precursor by the mechanochemical treatment. XRD, XPS, DTA, TPD of NH 3 and determination of catalytic activity and selectivity in n-butane oxidation have been carried out. The preparations studied after mechanochemical treatment in a planetary mill were: (a) VPO, composed of VOHPO 4 · 0.5H 2O, (b) VPBiO, containing the bismuth additive introduced during synthesis, (c) VPO/Bi 2O 3 and VPO/BiPO 4, mechanical mixtures of the VPO precursor and Bi 2O 3 or BiPO 4, respectively. Introduction of alkali and alkaline-earth metals additives increases the basicity of surface oxygen in vanadium pyrophosphate, which entails increase in the rate of n-butane oxidation. The mechanochemical treatment of the preparations changed their morphology, favouring the formation of the vanadyl (001) plane in the phosphate precursor. The XRD peaks of bismuth phosphate appeared instead of those of bismuth oxide and the +0.8 eV chemical shift in the XPS Bi4f band was observed. The change in the chemical state of VPO/Bi 2O 3 are an evidence of the occurrence of chemical reaction. Mechanochemical treatment of VPO/BiPO 4 and VPO/Bi 2O 3 catalysts increases their activity in n-butane oxidation and the selectivity to maleic anhydride. Thus, mechanochemistry may be a promising method for introduction of promoting additives into the basic VPO composition.