High-temperature interaction of solid Cu chlorides and Cu oxides in mixtures with H-forms of ZSM-5 and Y zeolites

Abstract

A high-temperature solid-state ion exchange between separate phases of solid Cu chlorides and hydrogen forms of ZSM-5 and Y zeolites occurs above 570 K and reaches substantial degrees at 770 and 670 K, respectively, i.e. at temperatures at which considerable self-dehydroxylation of the particular zeolite does not take place. The process has been followed using IR, EPR and MS techniques through the evolution of hydrochloric acid into the gaseous phase, the consumption of the bridging OH groups in the zeolite as well as by the formation of isolated Cu ions that exhibit strong electron-accepting properties. The exchange rate is very fast in the initial stage, being proportional to the amount of copper salt in the mixture, and levels off to zero after several hours. Owing to the more difficult deaggregation of Cu oxides compared to Cu chlorides, the interaction of Cu oxides with H-ZSM-5 and H-Y at 770 K and 670 K, respectively, results in a very limited consumption of the bridging OH groups as well as in a decreased formation of isolated Cu ions and electron-acceptor sites compared with the corresponding Cu chloride mixtures. Besides the ability of the copper phases (chlorides or oxides) to deaggregate, a further striking factor affecting the exchange reaction is the mobility of the zeolite protons and exchanged cations, which is controlled by the structure type of the zeolite and by the temperature. This is clearly reflected by the positive effect of the temperature on the exchange process and the higher degree of exchange (at a given temperature) found for H-Y zeolites compared with H-ZSM-5.