Structural Characteristics, Stability, and Activity of (VO)2P2O7 and VO(PO3)2 Catalysts in p-Cymene Liquid-Phase Oxidation

The post-reaction structural characteristics of VO(PO3)(2) and (VO)(2)P2O7 catalysts and their reusability in liquid-phase oxidation of p-cymene to tertiary cymene hydroperoxide (TCHP) are investigated and characterized. The VO(PO3)(2) structure remains unchanged after being used for extended reaction times, whereas (VO)(2)P2O7 undergoes structural changes back to its precursor phase, VOHPO4 center dot 0.5H(2)O, that affect its catalytic properties. The structure of the (VO)(2)P2O7 that has undergone phase changes is successfully restored by calcination under N-2 flow at 750 degrees C for 2 h. Fresh and used catalysts show different particle morphologies, indicating that the reaction medium influences the microstructure. Both catalysts show considerable reusability with (VO)(2)P2O7 showing slight gradual deactivation. Taking into account the characterization and catalytic results obtained, the slight (VO)(2)P2O7 deactivation can probably be ascribed to the adsorption of organic compounds on the catalyst surface, which appears to initiate structural transformation of the (VO)(2)P2O7 catalyst under oxidation reaction conditions for extended reaction times. The VO(PO3)(2) and (VO)(2)P2O7 catalysts showed to be effective for synthesis of the industrially important intermediate TCHP, a precursor to p-cresol in liquid-phase oxidation reactions.