Preparation Of SiO₂ Supported Metal Oxide Catalysts And Its Application In Oxidation Of Cyclohexane

Cyclohexane oxidation is a very important reaction process in the chemicalindustry.The product KA oil(the mixture of cyclohexanone and cyclohexanol)is an important reaction intermediate in the production of nylon 6 and nylon 66,and KA oil is also an important solvent in organic synthesis reactions,and is widely used in medicine,coatings,fibers and other industries.At present,the process of cyclohexane oxidation on the market is mainly uncatalyzed oxidation,which has high energy consumption,low conversion rate,poor selectivity and high environmental treatment cost.Cobalt and boric acid are the most commonly used catalysts in catalytic oxidation process,but these catalysts can cause damage to reaction equipment and recycling of homogeneous catalysts is inevitable.In order to achieve high efficiency and high selectivity of cyclohexane conversion,the development of a heterogeneous catalyst with high activity is currently the focus of research.Mesoporous silica because of its good porosity,high specific surface area and good chemical stability under the attention of many researchers,so choose it as a catalyst carrier,after doping active component preparation for silica load metal oxide catalyst and applied to selective oxidation of cyclohexane.A series of Cr/SiO2 catalysts under different heat treatment temperatures were prepared by an in-situ coprecipitation method using TEOS as silicon source and Cr(NO3)3·9H2O as chromium source.The structure and composition of the catalysts were investigated by XRD,XPS,FT-IR,SEM,TEM,H2-TPR and N2 adsorption and desorption.Then take cyclohexane selective oxidation reaction as probe reaction,by changing various reaction conditions such as:reaction temperature,reaction time,catalyst dosage,oxidizer dosage,solvent,etc.,explore the most appropriate reaction conditions of the system.Under the most suitable reaction conditions,the catalyst Cr/SiO2-400 obtained at the calcination temperature of 400℃ has the best catalytic activity,which can obtain 54.59%cyclohexane conversion rate and 90.01%KA oil selectivity.The main active valence states of Cr active components were obtained by the combination of the catalyst characterization results and activity test data.Finally in the best reactions under conditions of circulation use of test,the results showed that the catalyst in the process of circulation,with the increase of cycling times,cyclohexane conversion rate will be down,but the selectivity of KA oil can inhibit the stay above 90%,and the catalyst after the circulation use four still can get 45%cyclohexane conversion rate.On the basis of single metal catalyst Cr/SiO2-400,a series of bimetallic catalysts were prepared by selecting four metal elements Ce,Cu,La and Co using the same in situ coprecipitation method.The structure and composition of these catalysts were characterized and analyzed by XRD,XPS,FT-IR and SEM.The catalytic activity of these bimetallic catalysts was tested in the selective oxidation of cyclohexane.The results showed that the interaction between the two metals significantly improved the activity of CrCu/SiO2 catalyst when Cu was doped,and finally 61.81%cyclohexane conversion and 92.85%KA oil selectivity were achieved.