Kinetics of photoconversion of cyclohexane and benzene by LnVO4 and LnMo0.15V0.85O4 (Ln = Ce, Pr and Nd)

The orthovanadates LnVO(4), and molybdovanadates LnMo(0.15)V(0.85)O(4) (Ln=Ce, Pr and Nd), were synthesized via solid-state method. The crystal structure and the band gap of these compounds were determined by powder X-ray diffraction and UV-visible spectroscopy, respectively. The photocatalytic activities of these materials towards the oxidation of cyclohexane to cyclohexanol and cyclohexanone and towards hydroxylation of benzene to phenol were investigated. A detailed free radical mechanism for the oxidation of cyclohexane has been proposed and the reaction rate coefficients were determined. The hydroxylation of benzene to phenol was modeled using a simple series reaction mechanism. The rate coefficients show that CeVO4 exhibited superior photocatalytic activity and selectivity for the oxidation of cyclohexane to cyclohexanone compared to all other catalysts. For the hydroxylation of benzene, PrMo0.15V0.85O4 yielded high amounts of phenol. The observed trends in photoactivity are in good agreement with the band structure of these compounds. (C) 2008 Elsevier B.V. All rights reserved