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

Abstract

The post‐reaction structural characteristics of VO(PO3)2 and (VO)2P2O7 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)2P2O7 undergoes structural changes back to its precursor phase, VOHPO4⋅0.5 H2O, that affect its catalytic properties. The structure of the (VO)2P2O7 that has undergone phase changes is successfully restored by calcination under N2 flow at 750 °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)2P2O7 showing slight gradual deactivation. Taking into account the characterization and catalytic results obtained, the slight (VO)2P2O7 deactivation can probably be ascribed to the adsorption of organic compounds on the catalyst surface, which appears to initiate structural transformation of the (VO)2P2O7 catalyst under oxidation reaction conditions for extended reaction times. The VO(PO3)2 and (VO)2P2O7 catalysts showed to be effective for synthesis of the industrially important intermediate TCHP, a precursor to p‐cresol in liquid‐phase oxidation reactions.

Catalytic Activity and Structure Properties of Doped VOHPO<SUB>4</SUB>·0.5H<SUB>2</SUB>O with Nanosized Ru, Au, Fe and Mn in Benzene Hydroxylation

“…The short window period recyclability testing of nanosized doped-Au/VHP catalyst in the present study give only the rough estimation of its performance but not the true long-term performance deactivation that usually requires several hundred hours of on-stream testing. 22 This would require the use of a well-controlled reactor such as continuous-flow system (e.g., micro-channels or fixed-bed reactor) that will ensure uniform contact of reactants with the catalyst material for a prolonged usage period without the significant limitations imposed by the loss of the catalyst mass. Based on the succesfull application of nanosized dopedAu/VHP as effective hydroxylation catalyst for benzene reaction to phenol, we expanded the catalyst scope of application to other industrially important aromatics and cyclic ring hydrocarbons such as toluene, styrene and cyclohexane under the similar optimized reaction conditions.…”