Preparation Of High-efficiency Copper-based Catalysts And Exploration Of The Mechanism For Rochow Reaction Of Organosilicon Monomer Synthesis

Rochow reaction is the most important reaction in the industrial production of organosilicon monomer.Metal Si(also known as metallurgical silicon)can react with CH3Cl,HCl and alcohols to obtain different organosilicon monomers.Among them,trimethoxysilane(M3)is an important raw material for the synthesis of silane coupling agent,organosilicon terminated polyether,polypropionate sealant and adhesive in silicone industry.At present,the direct reaction of metal Si with CH3OH to prepare m3 by rochowreaction in the presence of Cu based catalyst is used in industry.However,there are still some problems,such as low selectivity of target product,unclear catalytic reaction mechanism and so on.Trichlorosilane(TCS)is the basic raw material for the production of solar polysilicon and electronic chip crystalline silicon.At present,it is prepared by the direct reaction of metal Si and HCl gas through non catalytic process in industry,which has the problems of high reaction temperature,high energy consumption and poor selectivity of target products.In order to solve these problems,based on rochowreaction,the following research work has been carried out in this paper:(1)In the "direct" synthesis of trimethoxysilane by the reaction of Si with methanol using the CuCl catalyst,there is the generation of a lot of HCl gas,thus causing severe reactor erosion and environmental pollution.In this work,to develop greener and more efficient composite catalysts to reduce the amount of CuCl,we employed three pretreatment methods to activate the contact mass consisting of Si powder and the composite catalyst of CuCl and Cu2O.It was found that the contact mass activated by argon(Ar),hydrogen argon(H2/Ar)and methyl chloride(CH3Cl),respectively,exhibited different catalytic performances:the highest Si conversion(34.1%)and M3 yield(24.0%)were obtained on the sample activated by CH3Cl.Notably,the M3 yield was increased 8-fold than that of the un-activated sample.The X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS)studies revealed that different activation methods led to the generation of different kinds of CuxSi phases such as Cu3Si and Cu4Si,both of which gradually transformed into Cu15Si4 during the reaction process.A clear dependency of M3 selectivity and yield on the amount of Cu15Si4 suggests that Cu15i4 is the active phase for selective synthesis of M3.Pretreatment of the contact mass with CH3Cl can promote the formation of CuxSi,which contributes to the generation of more Cu15Si4 active phase and thereby leads to superior catalytic performance.This work provides a new way to develop more efficient and greener catalysts in the "direct" synthesis process of M3.(2)Here we report the first synthesis of nearly pure-phased Cu3Si alloy that can be a highly efficient catalyst in the hydrochlorination of silicon reaction.This material was prepared by a high-temperature(1050℃)calcination method in which copper and silicon powders were used as the reactants.The X-ray photoelectron spectroscopy(XPS)study revealed that the Cu and Si atoms in the Cu3Si alloy carried part of positive and negative charge,respectively.When employed as the catalyst in the silicon hydrochlorination to TCS for the production of Si polycrystals for Solar cell,the sample Cu3Si exhibited excellent low-temperature catalytic performance:the Si conversion and TCS selectivity respectively achieved 41.1%and 96.1%at 250 ℃.Notably,its TCS yield at 250℃ was 1.2 times higher than that of the industrial catalyst-free system at 350℃.Detailed analysis of the reaction process showed that the positively charged Cu atoms and negatively charged Si atoms in Cu3Si alloy could cleave the H-Cl bond in the reactant HCl and make the combination of H and Cl atom with Si atoms easier.Meanwhile,the reaction between the remaining Cu atom and Si was accelerated,leading to the generation of more active Cu6.69Si and ultimately superior catalytic performance.This work deepens the fundamental understanding of the hydrochlorination of silicon reaction,and provides an avenue for the synthesis of Si-based alloy catalysts.