Abstract:
The direct functionalization of methane is very challenging due to the strong C-H bonds and its tetrahedral geometry. LaCl3 is a stable, active and selective catalyst for oxidative chlorination of methane with hydrogen chloride and oxygen to methyl chloride and water. In order to understand the reaction mechanism and to improve the selectivity, physico-chemical and kinetic studies were combined.
The reaction proceeds via transient surface OCl- species. In the postulated carbonium ion transition state, a hydrogen atom in methane is proposed to be substituted by Cl+. Methyl chloride is the primary product formed and can be further chlorinated or oxidized in sequential steps. In order to reach higher BET surface areas, the synthesis of the catalyst precursor, LaOCl, was improved by using organic bases for precipitation. The addition of other metal chlorides led to complex changes of the activity and selectivity without enhancing the properties of the catalysts essentially.