Study On Cyclohexene Oxidation Over Supported Nano Gold Catalyst Under Mild Conditions

Many useful products can be abtained from cyclohexene oxidation, such as cyclohexene oxide (raw material of agricultural chemical propargite), cyclohexane-1,2-diol (used to produce pyrocatechol),2-cyclohexene-1-ol and 2-cyclohexene-1-one (pharmaceutical intermediates), etc.. These four products mentioned above are collectively calledΣC6.The demands ofΣC6 increase a lot with the development of fine chemistry. However, as there is a C=C bound and fourα-H atoms in the cyclohexene molecule, the oxidation of cyclohexene is often inefficient because various products could be obtained at a time with unsatisfactory conversion or selectivity. Therefore, the research of heterogeneous catalysts for cyclohexene oxidation with good catalytic performance under mild conditions attracts the academic and industrial world.This theme includes six chapters, mainly reports carbon-supported gold catalyst, OMS-2 supported gold catalyst, HNTs supported gold catalyst, and their preparation methods, characterization and catalytic performance in cyclohexene oxidation. The theme is list in detail as follows:Chapter 1 gives a review about the progress of catalysts for cyclohexene oxidation in the last decade, mainly focusing on the nano gold catalysts, which has good catalytic performance under mild conditions.Chapter 2 introduces the experimental materials, experimental equipments, and the method of catalyst characterization and catalyst test. PTFE-lined autoclave (Capacity=30 mL, pressure maximum 6 MPa) was choosen for cyclohexene oxidation, n-heptane was used as internal standard for product analysis and catalysts were characterized by inductively coupled plasma-atomic emission spectrometry (ICP-AES), X-ray-diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), energy dispersive X-ray analysis (EDX) and Brunauer-Emmet-Teller (BET).Chapter 3 is about cyclohexene oxidation on carbon-supported gold catalysts. Carbon-supported gold catalysts Au/C were prepared by an impregnation-reduction method and characterized by ICP-AES, XRD and TEM. Au/C catalysts were modified by AgNO3 and Co(NO3)2·6H2O to obtain bi-metallic catalysts Au-Ag/C and Au-Co/C. Their catalytic performance was tested in the oxidation of cyclohexene in an autoclave without any solvent. The results showed that Ag doping can significantly enhance the catalytic performance of carbon-supported gold catalyst. Au(1.0 wt.%)-Ag(1.0 wt.%)/C has been found to be an efficient catalyst for the oxidation of cyclohexene with a conversion 27.6% at 80℃and 0.4 MPa for 12 h while selectivity forΣC6 products exceeding 88.9%, especially the selectivity of cyclohexane-1,2-diol up to 47.6%.Chapter 4 deals with solvent-free oxidation of cyclohexene over catalysts Au/OMS-2 and Au/La-OMS-2 with molecular oxygen. The OMS-2 supported gold catalyst with low gold loading and La doping has shown high efficiency for cyclohexene oxidation to 2-cyclocyhexene-1-ol and 2-cyclocyhexene-l-one. Au/La-OMS-2(0.24) was found to be an efficient catalyst for the oxidation of cyclohexene with a high conversion (48.0%). More than 84% selectivity for 2-cyclohexene-1-ol and 2-cyclohexene-l-one was obtained. The high activity and good stability of catalyst Au/La-OMS-2 is ascribed to both the effect of gold and the structure and composition of La-OMS-2.Chapter 5 deals with halloysite nanotubes (HNTs) supported gold catalyst. The selective oxidation of cyclohexene to 2-cyclohexene-1-ol and 2-cyclohexene-l-one has been investigated over Au/HNTs with molecular oxygen in a solvent-free system. The results show that the catalytic performance of Au/HNTs is well and the catalytic activity over recycled catalyst remains well. Moreover, the nano-size effect of gold is found for cyclohexene oxidation.Chapter 6 summarizes the main contents of the dissertation, and several research suggestions about cyclohexene oxidation on nano gold catalysts are proposed.