Catalytic Partial Oxidation of Cyclohexane by Bimetallic Ag/Pd Nanoparticles on Magnesium Oxide

5 years ago

Catalytic Partial Oxidation of Cyclohexane by Bimetallic Ag/Pd Nanoparticles on Magnesium Oxide

Graham J. Hutchings, Stuart H. Taylor, Keith Whiston, Qian He, David W. Knight, Xi Liu, Christopher J. Kiely, Marco Conte, Damien M. Murphy

The liquid-phase oxidation of cyclohexane to cyclohexanol and cyclohexanone was investigated by synthesizing and testing an array of heterogeneous catalysts comprising: monometallic Ag/MgO, monometallic Pd/MgO and a set of bimetallic AgPd/MgO catalysts. Interestingly, Ag/MgO was capable of a conversion comparable to current industrial routes of approximately 5 %, and with a high selectivity (up to 60 %) to cyclohexanol, thus making Ag/MgO an attractive system for the synthesis of intermediates for the manufacture of nylon fibres. Furthermore, following the doping of Ag nanoparticles with Pd, the conversion increased up to 10 % whilst simultaneously preserving a high selectivity to the alcohol. Scanning transmission electron microscopy and energy dispersive spectroscopy of the catalysts showed a systematic particle-size-composition variation with the smaller Ag–Pd nanoparticles being statistically richer in Pd. Analysis of the reaction mixture by electron paramagnetic resonance (EPR) spectroscopy coupled with the spin-trapping technique showed the presence of large amounts of alkoxy radicals, thus providing insights for a possible reaction mechanism. Trap my spin! AuPd/MgO nanoparticles were found to be active for the selective oxidation of cyclohexane to cyclohexanol and cyclohexanone. EPR spectroscopy study coupled with the spin-trapping technique showed the presence of large amounts of alkoxy radicals, thus providing insights for a possible reaction mechanism (see figure).

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201605941