Effects of mechanochemical treatment to the vanadium phosphate catalysts derived from VOPO4·2H2O

Modification by using mechanochemical treatment of vanadium phosphate catalysts on the microstructure, morphology, oxygen nature and catalytic performance for n-butane oxidation is described and discussed. In this work, the precursor, VOHPO4·0.5H2O prepared by reduction of VOPO4·2H2O by isobutyl alcohol was subjected to a high energy planetary ball mill for 30, 60 and 120 min in ethanol. The ball milling process reduced the crystallite size of the catalysts and consequently increased their surface area. The morphologies of the milled catalysts are dependent on milling time. The highest reactivity and mobility of the lattice oxygen species has been achieved by the catalyst milled for 60 min with lower reduction peak temperature and higher amount of oxygen atoms removed. The oxygen species removed from the active V4+ phase was shown to be correlated with the rate of reaction. A good relationship was also found between the oxygen species associated with V5+ and maleic anhydride selectivity. However, a larger amount of this oxygen species will give a deleterious effect on the conversion rate. The present study demonstrate that the mechanochemical method (with an appropriate duration) effectively enhanced the catalytic activity by increasing the surface area and controlling the reactivity, and that the amount of oxygen species contributed to the partial oxidation of n-butane to maleic anhydride.

Graphical abstractMechanochemically treated vanadium phosphate catalysts. Figure optionsDownload full-size imageDownload as PowerPoint slide