Study On Synthesis And Performance Of New Promoters Uesd In Organosilicon Monomer Synthesis

Dimethyldichlorosilane(M2)is the most important monomer in the silicone industry.Industrial technology is constantly innovating to increase the M2 yield.Currently,the Direct Process(known as Rochow-Muller reaction)is widely used in industry to synthesis M2,that is,the reaction between methyl chloride(CH3Cl)and silicon powder(Si)in the presence of copper(Cu)-based catalysts.The Cu-based catalyst is composed of the main catalyst and promoters,and the promoters has a significant effect on improving the catalytic performance of the main catalyst.However,there has been very few reports on promoters and the mechanism is still unclear so far.The catalytic performance of Cu-based catalysts has encountered a further improved technical bottleneck,which affects the market competitiveness of China's silicone products.Thus,in this paper,we selected CuO as the main catalyst to study the performance of a new type of catalyst,which used atomically dispersed Sn/Zn and atomically dispersed Sn1Ox as promoter.The micro-morphology,electronic structure and coordination environment of the catalyst were analyzed,and the synergistic catalytic effect and adsorption mechanism of the promoters were also discussed.The performance of a new copper-based catalyst(Zn1-Sn1/CuO)consisting of atomically dispersed Sn and Zn co-promoter on CuO was studied.CuO,Zni-Sn1/CuO,Zn-NP,Sn-NP/CuO were synthesized and evaluated for Rochow-Muller reaction activity and stability.The results show that the M2 selectivity and Si conversion of CuO catalyst are 33.1%and 3.0%,respectively,and the M2 selectivity and Si conversion of 0.1Zni-Sn1/CuO catalyst are 88.7%and 41.6%,2.7 and 13.8 times higher than those of CuO respectively.By comparing and analyzing the micro-morphology and electronic structure of different catalyst systems,it was found that there was a synergistic catalysis effect between the atomically dispersed Sn and Zn co-promoter in Zni-Sni/CuO.The synergistic catalytic mechanism of the promoters Zn and Sn atoms in Zn1-Sni/CuO was revealed.It was found that on the Sn-doped CuO(110)surface,the formation energy was 0.78 eV lower than that on the clean CuO(110),which can anchor Zn stably by using experimental characterization and theoretical calculation.Moreover,when Zn and Sn additives exist in the form of atoms,the synergistic interaction between single-site Sn and Zn pair leads to the change in the electronic structure of CuO catalyst,which promotes the adsorption of reactant CH3Cl and formation of the CuxSi active phase,thereby leading to the enhanced catalytic performance.The effect of different additives precursors on the catalytic performance of copper oxide catalyst(Sn1Ox/CuO)with atomically dispersed Sn1Ox was studied.SnCl4·5H2O and(CH3)2SnCl2 were selected as precursors,and the Sn1Ox/CuO systems with different Sn contents were synthesized by impregnation.Since some Sn atoms are incorporated into the CuO lattice by using(CH3)2SnCl2,resulting in the more content of Sn,the more evenly distributed on the surface and inside of CuO,so the performance of 1%Sn1Ox/CuO-Me catalyst is better than SniOx/CuO-Me.After applying SnCl4·5H2O,Sn atoms were loaded on the surface of CuO n the form of Sn1Ox evenly.So the catalytic performance decreased in sequence with the increase of the content of Sn and the performance of Sn1Ox/CuO is the best.The mechanism of atomically dispersed Sn1Ox was revealed.Using Rochow-Muller reaction and silicon hydrochlorination reaction to test the performance of Sn1Ox/CuO and the catalyst system loaded with SnOx-NP.It was found that Sn1Ox/CuO has good catalytic performance.It is because when Sn atoms exist in the form of Sn1Ox,electron cloud density of Cu and O elements on the surface of CuO could be enhanced simultaneously.And finally changed the electronic structure of the catalyst.The density functional theory calculation further confirms that the change in the electronic structure of CuO is of benefit to enhance the interaction between the catalyst and the dissociated adsorbed CH3 and Cl species,which helps to improve the selectivity of methyl-containing and hydrogen-containing products.