Location and functions of Zn as a promoter element in the VPO catalysts for n-butane oxidation to maleic anhydride

Abstract

Location of zinc in the VP0 catalysts containing zinc was examined along the preparation process. The mixture of H 4(VO) 2P 20 9, (NH 4) 2ZnCl 4, and NH 4ZnPO 4 was formed, when an aqueous solution containing VO 2+, Zn 2+, and NH 30HCI was evaporated to dryness. TG-DTA results of the mixture revealed that (NH 4) 2 ZnCl 4 decomposed to ZnO at 470–570 K and water molecules were eliminated from H 4(VO) 2P 20 9 to give (VO)2P207 at 670–700 K, then the solid phase reaction between (VO) 2P 20 7 and ZnO took place at 790–810 K without any loss of the weight. Addition of 10 at.% of ZnO addition to (VO) 2P 20 7 by mechanical mixing brought about drastic increase in the oxidation rate of the catalyst to VOP0 4. This may be responsible for the increase in the rate of catalytic n-butane oxidation without significant changes in the product distribution observed over the Zn-promoted VP0 catalysts.