Vanadyl hydrogenphosphate sesquihydrate VOHPO P 1.5H O was prepared by reduction of VOPO P 2H O suspended 4 2 4 2
Ε½ . in refluxed 1-butanol and activated at 4808C over 10 h on-stream to give VO P O , which revealed high specific activity 2 2 7 Ε½ . per unit surface area in the vapor-phase oxidation of n-butane. Cobalt-modified VO P O catalysts were prepared in the 2 2 7 present work by intercalating sesquihydrate precursor with cobaltous acetate employing 1-butanol as solvent. The catalysts prepared from cobalt-intercalated precursor showed high specific activity, but both selectivities to maleic anhydride and surface area decreased with increasing cobalt-contents. Presumably, intercalated cobalt species retarded topotactic dehydra-Ε½ . tion of layered precursor to afford crystalline active species VO P O , leading to an increase in unfavorable combustion 2 2 7 activity due to pentavalent b-VOPO species. The activity of catalysts prepared for reference by kneading vanadyl 4 hydrogenphosphate hydrates with an additive Co P O was interpreted as the variation in surface area, and cobalt has none 2 2 7 of positive effects in these catalysts.