Tuning the selectivity of MoOx supported catalysts for cyclohexane photo oxidehydrogenation

The photocatalytic properties of sulphated MoOx/gamma-Al2O3 catalysts in cyclohexane oxidative dehydrogenation have been determined in a two-dimensional fluidized bed photoreactor and compared to those of sulphated MoOx/TiO2 catalysts. Photocatalytic tests on MoOx/gamma-Al2O3 at 8 wt% MoO3 and various sulphate contents showed the selective (100%) formation of cyclohexene, without production of benzene, as instead found with MoOx/TiO2. These results show that the selectivity of photocatalytic cyclohexane oxydehydrogenation is dramatically influenced by the catalyst support. Maximum cyclohexane conversion and cyclohexene yield of 11% were obtained for SO4 content of 2.6 wt% at 120 degrees C. Physico-chemical characterisation of catalysts indicates the presence of both octahedral polymolybdate and sulphate species on alumina surface, as previously found for titania. Increasing sulphate load, thermogravimetry evidenced the presence of up to three sulphate species at different thermal stability. The lower activity observed at high sulphate content is likely due to polymolybdate decoration by sulphates. (c) 2007 Elsevier B.V. All rights reserved.