Catalytic cracking of CH3Cl on copper-based phases

Abstract

The methylchlorosilanes synthesis from Si and CH₃Cl, also called the direct synthesis suffers from a side-reaction during which the CH₃Cl reactant cracks and forms carbonaceous compounds, called coke. It leads to deactivation of the Cu₃Si active phase formed by reaction of Si and a Cu precursor. This paper deals with the CH₃Cl cracking on the copper-based phases CuCl and Cu, without and with Si (during the direct synthesis). In the former case, the two phases were supported either on carbon black or on silica. Both CuCl and Cu were shown to be active phases with similar reaction rate and the stoichiometry of the CH₃Cl cracking was determined from the selectivity values. Cu turns into CuCl by reacting with CH₃Cl. CuCl is stable on SiO₂ while it is reduced on carbon black support which is chlorinated during the cracking. This key result reveals an original effect of coke since it favours formation of metallic Cu inactive for the direct synthesis in addition to covering the active sites leading to deactivation.