Study On Preparation Of Modified Rice Straw Biochar Supported Platinum Catalyst And Properties In The Hydrosilylation Of Alkenes With Triethoxysilane

Alkyl silane synthesized by the reaction of terminal alkene and silane hydrosilane is a very important reactant in organosilication.It has high commercial application value and industrial production significance.Homogeneous platinum catalysts are the most important catalysts for this kind of reaction in industrial production.However,because the homogeneous platinum catalysts are difficult to be separated from the reactants,the recovery of the catalysts in industrial production is expensive and affects the product quality.In order to overcome this problem,this paper is devoted to the development of a porous activated carbon material as the support with high activity and high regional selectivity of heterogeneous platinum catalyst,and used in hydrosilylation of 1-hexene,1-octene,styrene with tertiary silane triethoxysilane(TES),the catalytic performance of the reaction was tested and kinetic study was carried out.The hybrid functional method B3 LYP was used to construct the reaction model and calculate the free energy of reaction activation.The main contents are as follows:1.Using agricultural waste rice straw as carbon source,porous biological activated carbon(RSAC)was prepared by proper carbonization and activation,and then used as a carrier for functional modification through reasonable oxidation(RSOC),adding appropriate ligand compounds vinyltriethoxysilane(VTES)and complexing platinum active components.A stable solid catalyst(Pt-VTES-RSOC)was successfully constructed on the surface of oxidized carbon of rice straw with a bivalent platinum vinyl complex as the active center.At the same time,control catalysts Pt-RSAC and Pt-RSOC were prepared with rice straw activated carbon(RSAC)and rice straw oxidized carbon(RSOC)respectively.The structures of these catalysts were characterized to study the effects of different support and coordination modification on the composition and structure of the active components of the catalysts.The results show that the average particle size of Pt particles in Pt-VTES-RSOC is only 1.36 nm,which has the characteristics of small particle size and high dispersion.However,Pt in Pt-RSAC and Pt-RSOC is mainly physically adsorbed in the pores on the surface of the carrier in the form of quadrivalent Pt ions,and the average particle size is large and easy to agglomerate.2.The catalytic performance of Pt-VTES-RSOC was tested,and the results showed that the catalyst had good catalytic performance for the hydrosilylation of different terminal olefins with TES.The β-product conversions of 1-hexene、1-octene and styrene reached 99.3 %、98.9 % and 97.8 %,respectively,at 50 ℃ for 3 h,and theβ-product selectivity was 98.4 %、96.6 % and 86.7 %,the catalytic activity was high,and the catalytic activity remained high after repeated use for 5 times.According to the kinetic study of the corresponding reaction,the apparent activation energy and reaction rate of 1-hexene and TES catalyzed by Pt-TES-RSOC were the lowest and the highest,and compared with the control catalyst,the apparent activation energy of the typical hydrosilylation was significantly reduced by the formation of the bivalent platinum vinyl complex on the surface of Pt-VTES-RSOC.3.The theoretical calculation results of Pt-VTES-RSOC catalytic main and side reactions of hydrosilylation on typical olefin systems show that the activation energy of α-addition byproduct transition state formed on the surface of Pt-VTES-RSOC is much higher than that of the main reaction,and the reaction rate constant under the calculated byproduct transition state is much lower than that of the main product.It can be seen that Pt-VTES-RSOC catalyzed the reaction is difficult to generate α-addition byproducts,so the selectivity of target products is high.However,in the aromatic olefin system,the activation energies of Pt-VTES-RSOC to form the transition states of main and byproducts on the surface are higher than those of straight-chain olefin,and the difference between the two is close,which leads to the poor selectivity of the target products when Pt-VTES-RSOC catalyzed the addition of styrene and TES.The above theoretical calculation results are in agreement with the experimental results,which shows the reliability of the theoretical calculation.