Study On Preparation And Catalytic Performance Of Supported Nanometer Gold Catalysts

The cyclohexane oxidation technology of great significancein the chemical production, for oxidation products cyclohexane,via cyclohexanol and cyclohexanone are important intermediate in the production of adipic acid and caprolactam However,the oxidation processes in the presence of the cyclohexane are energy intensive, have low conversion coefficients and total selectivity, generate environmentally hazaidous waste and byproducts. So is an urgent to receive low-cost, high conversion,selectivity simultaneously,stability and friendly environmentally by discovering a efficient cyclohexane oxidation catalyst.Based on the nano-gold catalyst with and structural stabiliyi of the characteristics,and the unique use of MCM-22 zeoite channels by using the shape-selecticity catalytic capacity,the nano-gold was supported on the moleculai sieve such as MCM-22, and preparation of surpported nano-gold catalyst with a good catalytic performance.Gold nanoparticles of the high activity of such catalysts require high temperature calcination to obtain the zero valent state, while the high temperature calcination causes the gold particles aggregation, sintering. This paper aimed to solve the problem and base on the photocatalytic properties of TiO2, nano-gold was deposited into the inner or outer of titania-modified MCM-22 by photodeposition method. Samples of the catalysts characterized by XRD, ICP, SEM.Cyclohexane oxidation reaction as a model reaction to evaluate the catalytic performance, and the use of MCM-22 zeolite carrier of the hydrophobic oleophilic tunnel effect and shape selective role to improve the conversion of the cyclohexane oxidation reaction rate and desired product selectivity.The catalytic performance of these samples for the cyloheane liquid-oxidation into cylohexanone and cyclohexanol by O2 in the agsence of solvents is investigaed. The following results and conclusion have been obtained:(1)MCM-22 is a good catalyst suport for the selective oxidation of cyclohexane. Sieves with specipal pore structure and shpa-selective performance have the ability to improve the conversion and selecticity of cyclohexane partial oxidation;Pure silica sieve MCM-22 has great specific surface area favoring the TiO2and Au,which can improve the catalyst activity.(2)Supported nano-gold catalyst Au/MCM-22 prepared by deposition precipitation.It is an effective catalyst for the cyclohexane oxidation to cyclohexanol and cyclohexanone. The conversion of cyclohexane was 10.43 and the total selectivity of desired products was92.07%under the conditions of Au/MCM-22(wt0.75%) 150℃,1.0Mpa,reaction time 1.0h.(3)The comlex catalyst Au@TiO2/MCM-22 was prepared by the photodeposition method. It is an more effective catalyst for the cyclohexane oxidation to cyclohexanol and cyclohexanone. The conversion of cyclohexane was 11.45% and the total selectivity of desired products was90.72% under the conditions of Au@TiO2/MCM-22 (wt0.5%)150℃,1.0Mpa,reaction time 1.0h.