Effect of Copper Catalyst Content and Zinc Promoter on Carbon Formation in the Direct Synthesis of Methylchlorosilanes

Abstract

Direct synthesis of methylchlorosilanes (MCS) is a complex solid–gas–solid reaction where solid silicon (Si) reacts with chloromethane (CH3Cl) in the presence of a copper (Cu)-based catalyst, and coke formation by cracking of CH3Cl is a severe problem for this process. In this study, the effects of the Cu/Si ratio and Zn promoter on the MCS catalytic performance have been investigated in a fluidized bed lab-scale reactor (semibatch mode). Pre- and postcharacterization (SEM, XRD, Raman and DRIFTS spectroscopy, and TGA/DCS/MS) were performed to gain insights into the structure and reactivity of the carbonaceous species, the formation of active (Cu3Si) and unselective/coke-promoting (CuxSiy, Cu0) phases. A higher content of the CuCl catalyst (5 × Cu) boosts the Si consumption and initial reactivity with little effect on dimethyldichlorosilane ((CH3)2SiCl2; “M2”) selectivity other than a slightly longer induction period relative to the standard Cu/Si ratio, but it also promotes formation of undesired phases and hence coke. The effect of Zn promotion (in conjunction with Sn) is difficult to discern with standard amounts of CuCl and Zn added to the contact mass, but with increased amounts, Zn clearly facilitates the formation of the active catalytic phase and also appears to render the amorphous carbonaceous species formed somewhat more structurally ordered and H-depleted. The work expands our understanding of the MCS synthesis since both the Cu/Si ratio and Zn promotion affect the mechanisms as well as the propensity to form coke.