Effect of surface functionalization of cerium-doped MCM-48 on its catalytic performance for liquid-phase free-solvent oxidation of cyclohexane with molecular oxygen

Ce-doped MCM-48 (Ce-MCM-48) mesoporous molecular sieve was prepared hydrothermally and its surface was modified with organic groups or fluorine, and their physicochemical properties were characterized by XRD, low-temperature N-2 adsorption, TEM, UV-visible and FT-IR spectroscopies, XPS and contact angle measurement. The results indicated that Ce species were highly dispersed on the MCM-48 materials as Ce3+ and Ce4+. After post-functionalization of Ce-MCM-48, the organic groups or fluorine species have been immobilized on the surface of Ce-MCM-48, but the chemical status of Ce species were hardly changed, and the post-functionalization improved the surface hydrophobicity of the Ce-MCM-48 sample. The catalytic activity testing for the oxidation of cyclohexane with molecular oxygen showed that, Ce-MCM-48 after post-functionalization exhibited the higher cyclohexane conversion and selectivity to cyclohexanol and cyclohexanone, 8.9% cyclohexane conversion with 91.2% selectivity to cyclohexanone and cyclohexanol could be achieved over the Ce-MCM-48 with F-modified catalyst, which was attributed to the proper modification of their surface properties including hydrophobicity and polarity. The F-modified catalyst also showed excellent reusability, and its catalytic performance has no obvious deterioration after being repeatedly used five times. (C) 2015 Elsevier Inc. All rights reserved.