CHLOROMETHOXYL AND DICHLOROMETHOXYL FORMATION ON ZEOLITE ZNY, AN IN-SITU NMR AND FLOW REACTOR STUDY

In situ C-13 and Al-27 MAS NMR and flow reactor studies were used to s tudy the decomposition of dichloromethane and chloroform on zeolite Zn Y. The initially formed products were framework-bound chloromethoxyl ( from dichloromethane) and dichloromethoxyl (from chloroform) species, analogous to the non-halogenated alkoxyls observed in previous investi gations. The principal components of the C-13 chemical shift tensors w ere: chloromethoxyl, delta(11) = 116 ppm, delta(22) = 79 ppm and delta (33) = 37 ppm; dichloromethoxyl, delta(11) = 128 ppm, delta(22) = 91 p pm and delta(33) = 65 ppm. Formation of both species occurred at 298 K , and each decomposed at 423 K. This decomposition formed HCl which de aluminated the zeolite (as monitored by Al-27 MAS NMR) causing deactiv ation (flow reactor studies). Further evidence for the destruction of the zeolite was the NMR observation of CO formation, implying incorpor ation of oxygen from zinc hydroxyl or framework sites. Although ZnY is shown to be unsuitable for catalytic chlorocarbon destruction, the ob servation of chloromethoxyl and dichloromethoxyl species is significan t, and the formation of halogenated alkoxyl species should be consider ed in future investigations of halocarbon chemistry on oxides and mole cular sieves.