Selective oxidation of n -butane in the presence of vanadyl pyrophosphates synthesized by intercalation-exfoliation-reduction of layered VOPO 4·2H2O in 2-butanol

Abstract

Several vanadyl pyrophosphates ((VO)2P2O 7) with a different microcrystallite structure have been synthesized by a unique process involving the intercalation, exfoliation, and reduction of VOPO4·2H2O. Stepwise thermal treatment of a suspension of VOPO4·2H2O crystallites in 2-butanol caused the subsequent processes (intercalation, exfoliation, and reduction) to form VOHPO4·0.5H2O phases. The resulting VOHPO 4·0.5H2O phases were approximately 1-2 μm in lengths and roughly 0.1 μm in thickness with leaf-like shapes. The catalyst derived from the present novel processes was found to be more active and selective (78% selectivity at about 60% conversion at 663 K) than well-known rose-like crystallites (∼1μm) by the "organic solvent method" using iso-butanol and benzyl alcohol. The higher activity of the novel catalyst is attributed to the high surface area (approximately 30m2g -1 after the reaction for 200 h), and the higher selectivity is probably attributable to the pure phase of (VO)2P2O 7 because of the smaller dimensions of the crystallites and the preferential exposure of the basal plane of (VO)2P2O 7 due to the leaf shape. © 2003 Elsevier Inc. All rights reserved.