Applied Catalysis A: General, Vol.579, 30-43, 2019
Supported PtxPd1-x bimetallic nanoparticles on ionic liquid-functionalized SiO2@graphene oxide nanocomposite and its application as an effective multiphasic catalyst
In this work, PtxPd1-x (x = 0, 0.5, and 1) nanoparticles (NPs) were synthesized on the surface of SiO2@graphene oxide which covered by 1-butyl-3-methylimidazolium hexafluorophosphate ([bmitn] PF6) ionic liquid (IL) layer. FT-IR spectroscopy, zeta potential, CHN elemental analysis, XRD, XPS, SEM, EDX, TEM, TGA, BET, and ICP-AES techniques were applied for the characterization of the multiphasic catalyst. The as-prepared nanocomposite was used as an effective heterogeneous catalyst for the oxidation of cyclohexene by molecular oxygen, as a green oxidant. Different experimental conditions such as oxygen pressure, reaction time, reaction temperature and amount of catalyst were investigated in this reaction. The bimetallic NPs showed the best catalytic activity in this reaction. The conversion and selectivity of 2-cyclohexene-1-one as main product were obtained to be 65% and 93% respectively, when the reaction was carried at 80 degrees C for 8 h. In the as-made multiphasic catalyst, IL layer not only enhanced the stability of NPs on the surface of catalyst, but also increased the catalytic performance due to the stabilization of the reaction intermediates. Among the different solvathochromic parameters, the normalized polarity (E-T(N)) and the hydrogen-bond acceptor ability (beta) of IL are the most important properties which improve the role of the IL as a co-catalyst in this reaction. This multiphasic catalyst, which has the advantages of both homogeneous and heterogeneous catalytic systems, can be easily separated from the reaction media and reused for five consecutive runs without losing the catalytic performance.