Co/Sio₂ Catalysts Prepared By Electroless Deposition For The Catalytic Oxidation Of Cyclohexene

Oxidation of cyclohexene is a very important reaction in industrial production.In this project,the cobalt active component was deposited on SiO₂ as a catalyst by electroless deposition,and its catalytic activity for catalyzing the oxidation of cyclohexene was explored.?1?SiO₂-supported Co active center catalyst was prepared by electroless deposition,and the effects of substrate type,matrix pretreatment method,plating solution configuration,and plating solution pH on the catalytic activity of the prepared catalyst were investigated,when the nano-SiO₂ powder was used as the matrix,CoSO₄·7H₂O as main salt?0.6277g/L-11.927 g/L?,the NaH₂PO₂·H₂O as reducing agent?32 g/L?,the Na₃C₆H₅O₇?2H₂O as complexing agent?20 g/L?and the H₃BO3 as buffering agent?20 g/L?and Co/SiO₂-ELD-X catalysts with different cobalt contents can be prepared.?2?The catalysts were characterized by XRD,XPS,TEM,EDX and selected-area electron diffraction.It was found that the coating surface of all catalysts was mainly in the oxidation state of Co,Among them,in the Co/SiO₂-ELD-1 and Co/SiO₂-ELD-2 catalysts,the coating mainly contains amorphous Co,and the Co in the Co/SiO₂-ELD-3-5 catalysts coating is a hexagonal phase crystal structure,which indicates that the Co content in the Co/SiO₂-ELD-X catalyst has a direct influence on the amount of Co.when the Co content is small,the Co layer is an amorphous structure.When the Co content is large,the Co layer is transformed into a hexagonal phase crystal structure.?3?The catalytic activity of Co/SiO₂-ELD-X catalysts in the oxidation of cyclohexene was investigated at low temperatures using molecular oxygen as the oxygen source and without solvent.The Co/SiO₂-ELD-2 catalyst exhibits a higher catalytic activity.The main reason is that in the Co/SiO₂-ELD-X catalyst,the content of Co in the coating and the crystal structure determine the catalytic performance.When Co is in an amorphous state,its unique atomic arrangement may lead to enhanced catalytic performance of the active sites and uniform dispersion,so Co/SiO₂-ELD-2 catalyst can show high catalytic activity in cyclohexene oxidation.Using Co/SiO₂-ELD-2 as a catalyst,the effects of reaction temperature,time,amount of catalyst and oxygen pressure on the oxidation of cyclohexene were investigated.Under the optimal conditions,the reaction temperature was 329 K,the reaction time was 6 h,the amount of catalyst Co/SiO₂-ELD-2 was 14.5 mg,the oxygen pressure was 0.2 MPa,and the conversion of cyclohexene was as high as 49.8%,the total selectivity of the main product is 83.8%.The Co/SiO₂-ELD-2 catalyst has been subjected to a cyclic test,and its catalytic activity is not stable.There are two possible causes.One is that the catalyst loses the Co active component in the cyclohexene oxidation reaction,and the other is that during the recycling process,carbon deposits are generated and cover the active sites on the catalyst surface.