Study On The Photocatalytic Dehydrogenation Of Cyclohexane To Cyclohexene By Tungsten Trioxide

Cyclohexene is the intermediate for the synthesis of many important organic compounds.It is considered as the best raw material for the synthesis of cyclohexanol,cyclohexanone and adipic acid.The production of polyester and other fine chemical products has an extremely important industrial application prospect.With the increasing demand for nylon products in China,and the demand for nylon 6 and nylon 66 in the world is also very large.However,the annual production of cyclohexene in China is very low due to the limitation of production technology.The existing production methods of cyclohexene have high cost,low efficiency and serious pollution,so it is urgent to find a new way to produce cyclohexene.Based on the above research background,the photocatalytic dehydrogenation of cyclohexane to cyclohexene was investigated using tungsten trioxide as the model catalyst,The relationship between the surface oxygen defects of tungsten trioxide and the selective conversion of cyclohexane and the mechanism of the effect of tungsten trioxide{001} crystal plane on the dehydrogenation of cyclohexane were further studied.(1)It provides a new way of photocatalytic dehydrogenation of alkanes,specifically,a highly selective method of photocatalytic dehydrogenation of cyclohexane to cyclohexene.Cyclohexene is dehydrogenated from cyclohexane at room temperature and atmospheric pressure to form cyclohexene.The selectivity of cyclohexene is as high as 100,and no by-products are produced.The whole process can be carried out in simulated sunlight.At the same time,the photocatalyst has good stability and has no obvious attenuation for a long time.The reaction conditions are mild and the operation is simple.The problems of excessive dehydrogenation of cyclohexane to benzene-by-products and oxidation of ketone alcohols were solved.(2)The factors affecting the dehydrogenation of cyclohexane under photoreaction conditions and its mechanism were studied by various means.The results showed that the high catalytic activity of WO3-X was directly related to its rich oxygen vacancy concentration.The results of further theoretical calculations also show that the existence of oxygen vacancies reduces the adsorption energy of cyclohexane,which is conducive to the adsorption of cyclohexane and promotes the efficient conversion of cyclohexane.This also explains why the catalytic performance of WO3-X is better than that of WO3.The intermediate product of cyclohexane dehydrogenation is also detected on line by EPR and the reaction pathway is discussed.The results showed that the conversion of intermediate products was promoted by light,and the conversion of cyclohexane was realized.At the same time,the action of oxygen molecules in the reaction process was obtained by the experiments of activity and kinetics under the condition of no oxygen.Moreover,the action of oxygen molecule was proved again by oxygen 18 isotope labeled W18O3.Finally,the production and consumption of surface hydroxyl groups and the production of water were detected by in situ infrared method.The dehydrogenation pathway of cyclohexane was proved.First,cyclohexane adsorbs on WO3-X to form WO3-X*C6H12,then WO3-X surface oxygen attacks C6H12 adsorbed on the surface,and the first H atom removes to form OH*WO3-X*C6H11.The second H get C6H10,and two molecules form a molecule of water on the surface of the hydroxyl group.Finally,cyclohexene molecules are desorbed due to poor adsorption of cyclohexene on the WO3-X surface.