Study On Selective Catalytic Oxidation Of Cyclohexene With High Activity Over Molybdenum-based Catalyst

Cyclohexene oxidation is an important catalytic reaction in industrial synthesis and its reaction products are widely used in many fields.Cyclohexene molecule has activeαhydrogen atom and carbon-carbon double bond.The special structure of cyclohexene leads to many paths and complex oxidation process,and the selectivity of target product needs to be improved.In addition,with the rapid economic development since the 21st century,the trend of green chemistry has become more and more obvious.The catalysts used in olefin oxidation reaction are mainly homogeneous catalysts,such as metal porphyrins and high transition metal complexes,but homogeneous catalysts are difficult to separate and recover from the system and did not meet the requirements of reusable green environmental protection.The multiphase catalysts currently studied have the disadvantages of low catalytic activity and low product selectivity.However,molybdenum base oxides are mostly solid substances and can be better separated from the system.They are environment-friendly catalysts and they can overcome the problems of complex operation,harsh conditions and environmental pollution in the traditional process.It has been reported that molybdenum catalysts are competent catalysts in selective oxidation and oxidative dehydrogenation of olefin due to their special crystal structure.However,their catalytic competencies in catalyst for selective oxidation of cyclohexene is rarely reported.The first part focuses on the hydrothermal synthesis method,using ammonium molybdate tetrahydrate,sodium molybdate dihydrate as different molybdenum sources,bismuth nitrate pentahydrate as bismuth source,cetyltrimethyl ammonium bromide,citric acid as additives,synthesis of bismuth molybdate catalyst.The catalysts were characterized by XRD,FT-IR,UV-vis,N₂ adsorption-desorption and water contact angle under scanning electron microscope and transmission electron microscope to explore the activity characteristics of the catalysts and the characteristics of cyclohexene oxidation under different reaction conditions.Experimental results showed that in four hydrated ammonium molybdate and five hydration bismuth nitrate as raw material preparation bismuth molybdate catalysts,hydrogen peroxide as oxidant,acetonitrile as the solvent,in 60℃temperature under two hours,preparation of epoxy cyclohexane oxidation of cyclohexene has more obvious results,one of cyclohexene conversion rate reached 77.0%,the selectivity of epoxy cyclohexane is 83.6%.In the second part,a mono-metal molybdenum oxide catalyst for cyclohexene catalytic oxidation was prepared by high temperature calcination with ammonium molybdate tetrahydrate as raw material.The catalysts were characterized by XRD,N₂ adsorption-desorption,SEM and FT-IR.The catalytic oxidation of cyclohexene to trans 1,2-cyclohexanediol by molybdenum oxide catalyst was investigated under different calcination temperatures,calcination time and calcination atmosphere.Experimental results show that Mo O₃ catalyst prepared by calcination of ammonium molybdate tetrahydrate at 550℃for 5 h has the best catalytic performance,with cyclohexene conversion of 91.6%and selectivity of 1,2-cyclohexanediol of 79.0%.The third part on the basis of the first part of the work,in order to reduce the cost of catalyst,inorganic polymer materials（TS-1,Si O₂,γ-Al₂O₃）as a carr1ier,using hydrothermal synthesis method to prepare a series of catalysts.XRD,N₂adsorption-desorption,scanning electron microscopy and other characterization techniques were used to analyze the catalysts.The influence of different support on the performance of the catalyst was studied.The catalytic activity of the catalyst for cyclohexene oxidation and the influence of different catalyst systems on the selectivity of oxidation products were tested.The results showed that the catalytic activity of Bi₂Mo O₆/TS-1 catalyst increased by 12.6%under the same conditions.Using Bi₂Mo O₆/Si O₂ as catalyst,the cyclohexene conversion increased by 27.3%,and the selectivity of cyclohexane oxide increased from 10.9%to 42.3%.Using Bi₂Mo O₆/γ-Al₂O₃ as catalyst,the cyclohexene conversion increased by 16.4%,and the selectivity of cyclohexene increased from 28.0% to 42.4%.