Location of zinc in the VP0 catalysts containing zinc was examined along the preparation process. The mixture of H4(VO)2P209, (NH4)2ZnCl4, and NH4ZnPO4 was formed, when an aqueous solution containing VO2+, Zn2+, and NH30HCI was evaporated to dryness. TG-DTA results of the mixture revealed that (NH4)2 ZnCl4 decomposed to ZnO at 470-570 K and water molecules were eliminated from H4(VO)2P209 to give (VO)2P207 at 670-700 K, then the solid phase reaction between (VO)2P207 and ZnO took place at 790-810 K without any loss of the weight. Addition of 10 at.% of ZnO addition to (VO)2P207 by mechanical mixing brought about drastic increase in the oxidation rate of the catalyst to VOP04. 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 VP0 catalysts.
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