Characterisation and long-term usage catalytic properties of (VO)2P2O7/γ-Al2O3 stainless steel coated catalyst in p-cymene oxidation

(VO)(2)P2O7/gamma-Al2O3 catalyst was coated onto a stainless steel plate in order to evaluate the long-term catalytic performance and the (VO)(2)P2O7 catalyst structure behaviour in liquid phase oxidation of p-cymene in a continuous simulated on-stream test. The stainless steel coated catalyst (containing 11 wt% loading) displayed a slow, yet significant deactivation over an extended reaction period of up to 250 h on-stream testing. Comparable results to the pure (VO)(2)P2O7 and (VO)(2)P2O7/gamma-Al2O3 supported catalysts with the stainless steel coated catalyst was obtained with tertiary cymene hydroperoxide (TCHP) selectivity in a range of 75-85% giving 20-30% yield at conversions between 25 and 40%. The activity of the stainless steel coated catalyst was only partially regenerated by calcination at 550 degrees C for 4 h, thereafter it showed a rapid activity drop in further catalytic testing. Powder XRD structural analysis of the used (VO)(2)P2O7 catalyst after continuous 75 h showed that the catalyst converted back to its precursor, VOHPO4 center dot 0.5H(2)O phase during oxidation reaction. The TGA-MS of the same used catalyst sample showed the loss of higher mass fragments (m/z) at decomposition temperatures of 350-800 degrees C indicating that considerable poisoning of the catalyst surface occurred during its continuous use. (C) 2009 Elsevier B.V. All rights reserved.