Study On The Preparation Of Nano-sized Gold Complex Catalyst And Its Catalytic Performance For Cyclohexane Oxidation Under The Mild Condition

The oxidation of cyclohexane to cyclohexanol and cyclohexanone is a key process in the chemical industry,for the oxidation products of cyclohexane,via cyclohexanol and cyclohexanone,are important intermediates in the prodution of caprolactam and adipic acid which are used in the manufacture of nylon-6 and nylon-66 polymers.However,the current processes are energy intensive,have low conversion coefficients and total selectivity,generate environmentally hazardous waste and byproducts,so it continues to be a challenge to receive high conversion and selectivity simultaneously under mild conditions by discovering a novel and efficient catalyst.Based on the photocatalytic property of TiO₂ and the high catalytic actvity of nano-gold,aimed to solve the problem it is difficult for cyclohexane oxidation with high selectivity under mild conditions,nano-gold or nano-silver were deposited into the inner or outer surface of titania-modified MCM-41 by the photodeposition method.This complex catalyst can be used not only the excellent shape-selectivity performance and the hydrophobe quality of MCM-41,but the especial photocatalytic performance of TiO₂ and the synergistic effect between Au and TiO₂,which is to receive high conversion and selectivity simultaneously for cyclohexane oxidation.The catalytic performance of these samples for the cyclohexane liquid-oxidation into cyclohexanone and cyclohexanol by O₂ in the absence of solvents is investigated.The following results and conclusion have been obtained:(1) MCM-41 is a good catalyst support for the selective oxidation of cyclohexane. Sieves with special pore structure and shape-selective performance have the ability to improve the selectivity of cyclohexane partial oxidation;Pure silica sieve MCM-41 has great specific surface area favoring the TiO₂ and gold particles dispersion,which can improve the catalyst activity.(2) The complex catalyst Au@TiO₂/MCM-41 was prepared by the photodeposition method.It is an effective catalyst for the cyclohexane oxidation to cyclohexanol and cyclohexanone in mild conditions.The complex catalysts have low-temperature and high catalytic acticity,due to the synergistic effect of nano-sized gold and photocatalysis.The conversion of cyclohexane was 3.9%and the total selectivity of desired products was 90.2%under the condiotions of 373K,1.0MPa,illuminated by 250 W UV-lamp for 8h.(3) Based on perparing nano-gold catalyst,a series of Au-Ag bimetallic catalyst samples were synthesized by the photodeposition method two times.Their catalytic performance for cyclohexane oxidation was investigated.The results showed that bimetallic catalyst showed better catalysis preformance than monometallic catalysts,the Au-Ag bimetal system shows a strongly synergistic effect with the right Au/Ag molar ratios.The conversion of cyclohexanc was 4.9%and the total selectivity of desired products was 92.3%under the condiotions of 393K,1.0MPa,(mor)Ag/Au=3:1,illuminated by 250 W UV-lamp for 5.5h.