Preparation Of Two Kinds Of Solid Acid Catalysts And Their Catalytic Selective Oxidation Properties For Hydrocarbons

In the field of petrochemicals and fine chemicals,acid catalysts play a very important role.Liquid acids with high catalytic activity been widely used in industrial production,however,its shortcomings are obvious,such as polluting the environment,corroding equipment and separate products hardly.In order to overcome the shortcomings of liquid acid,researchers have introduced solid acids into the acid catalysis field to replace the liquid acids,which has become a hot spot in catalytic research in recent years.Solid acid has high catalytic activity,good selectivity,high reusability and low corrosion to equipment compared with traditional liquid acid.The advantages of solid acid are favored by researchers.The selective oxidation of hydrocarbons to the corresponding ketones(alcohols)or epoxides is considered to be one of the most basic organic reactions and an important route for the introduction of oxygen atoms.The products are widely used in the field of fine chemicals.In this paper,a composite metal oxide was prepared by sol-gel method and bimetallic phosphate solid acid catalysts were prepared by sol-gel and ion exchange method.They were used for the selective oxidation of the above-mentioned hydrocarbons and the epoxidation of olefins.The solid acid catalysts were carried out by X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FT-IR),X-ray photoelectron spectroscopy(XPS),transmission electron microscopy(TEM)and scanning electron microscopy(SEM).Characterization,the main contents are as follows:(1)In this work,amorphous copper-chromium catalysts with different Cu/Cr molar ratios have been prepared by a sol-gel method and were used in the oxidation of cyclohexane to KA-oil.XRD results confirmed that the formation of amorphous structure.The XPS and Raman results indicated that most of Cu species existed in well-dispersed tetrahedral coordination before calcination.After calcination,the tetrahedrally coordinated Cu ions are transformed into octahedral coordination and the activity of catalyst is significantly reduced.The results show that the tetrahedrally coordinated Cu ions play the synergistic catalytic role with Cr ions.Interestingly,oxidation of cyclohexane is more inclined to produce cyclohexanol with uncalcined catalyst due to the presence of the tetrahedrally coordinated Cu ions;however,the appearance of surface lattice oxygen makes the reaction more conducive to cyclohexanone after calcination.After optimizing conditions,Cu-Cr oxide catalyst with the molar ratio 1:1 shows the highest activity,which obtains 62.2%yield and 92.4%selectivity for KA-oil using H2O2 as oxygen source.(2)The chromium-zirconium phosphate catalysts with different Cr/Zr molar ratios have been prepared by a sol-gel method and were used in the oxidation of different hydrocarbons(such as cyclohexane,cyclohexene and ethylbenzene)under oxygen(O2),hydrogen peroxide(H2O2)and t-butyl hydroperoxide(TBHP)as oxygen source.The product is mainly the corresponding alcohol ketone.The results show that the chromium ions into the mesoporous zirconium phosphate framework leads to a decrease in the specific surface area of the catalyst,but the CrZr2P and CrZrP catalysts still retain the mesoporous structure and form a composite metal phosphate,while the Cr2ZrP mesoporous structure disappears.The change of phosphate structure not only changes the specific surface area,but also changes the ratio of strong acid(including medium strong acid)and total acid amount on the catalyst surface.The different acid sites are more uniformly dispersed in the mesoporous structure,and the reactants can efficiently contact the acid centers,so that the catalyst exhibits excellent activity in selective oxidation of hydrocarbons.In addition,a certain amount of hexavalent chromium ions exist in the mesoporous skeleton,which can effectively improve the selectivity of the C=O product.(3)Transition metal exchanged ?/?-ZrP catalyst prepared by ion exchange method,using molecular oxygen as oxygen source under normal pressure to epoxidize styrene to styrene oxide.By screening the catalyst,it was found that the catalytic effect of Co-y-ZrP was relatively good and the optimized reaction conditions could obtain 91.75%styrene conversion and 68.44%styrene oxide selectivity.By characterizing Co-y-ZrP(5%),we found that the layered spatial structure of the catalyst remained intact after the reaction,indicating that the thermal stability of the catalyst was excellent.Interestingly,according to the recovered Co-y-ZrP(5%),characterization data,it can be seen that the tetrahedral coordination cobalt ion content in the catalyst is significantly increased,which may be the conversion of cobalt ions into tetrahedral coordination cobalt ions in the environment of DMF as solvent.The tetrahedral coordination cobalt ions played an active center role in the reaction process.