Selective oxidation of n-butane in the presence of vanadyl pyrophosphates synthesized by intercalation-exfoliation-reduction of layered VOPO4 • 2H2O in 2-butanol

Several vanadyl pyrophosphates ((VO)(2)P2O7) with a different microcrystallite structure have been synthesized by a unique process involving the intercalation, exfoliation, and reduction of VOPO4 . 2H(2)O. Stepwise thermal treatment of a suspension of VOPO4 . 2H(2)O crystallites in 2-butanol caused the subsequent processes (intercalation, exfoliation, and reduction) to form VOHPO4 . 0.5H(2)O phases. The resulting VOHPO4 . 0.5H(2)O phases were approximately 1-2 mum in lengths and roughly 0.1 mum 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 (similar to1 mum) 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 30 m(2) g(-1) after the reaction for 200 h), and the higher selectivity is probably attributable to the pure phase of (VO)(2)P2O7 because of the smaller dimensions of the crystallites and the preferential exposure of the basal plane of (VO)(2)P2O7 due to the leaf shape. (C) 2003 Elsevier Inc. All rights reserved.