Chloromethoxyl and dichloromethoxyl formation on zeolite ZnY, an in situ NMR and flow reactor study

In situ13C and27Al MAS NMR and flow reactor studies were used to study the decomposition of dichloromethane and chloroform on zeolite ZnY. The initially formed products were framework-bound chloromethoxyl (from dichloromethane) and dichloromethoxyl (from chloroform) species, analogous to the non-halogenated alkoxyls observed in previous investigations. The principal components of the13C chemical shift tensors were: chloromethoxyl,δ11 = 116 ppm,δ22 = 79 ppm andδ33 = 37 ppm; dichloromethoxyl,δ11= 128 ppm,δ22= 91 ppm andδ33 = 65 ppm. Formation of both species occurred at 298 K, and each decomposed at 423 K. This decomposition formed HCl which dealuminated the zeolite (as monitored by27Al MAS NMR) causing deactivation (flow reactor studies). Further evidence for the destruction of the zeolite was the NMR observation of CO formation, implying incorporation of oxygen from zinc hydroxyl or framework sites. Although ZnY is shown to be unsuitable for catalytic chlorocarbon destruction, the observation of chloromethoxyl and dichloromethoxyl species is significant, and the formation of halogenated alkoxyl species should be considered in future investigations of halocarbon chemistry on oxides and molecular sieves.