A comparative study of zeolites SSZ-33 and MCM-68 for hydrocarbon trap applications

Zeolites SSZ-33 and MCM-68, both possessing 12- and 10-membered ring pores, have been evaluated for use as a hydrocarbon trap employing temperature-programmed desorption (TPD) of toluene as a model system. SSZ-33 possesses a 12 × 12 × 10 pore system with a Si/Al ratio of 20, while MCM-68 has a 12 × 10 × 10 pore structure and can be synthesized with a Si/Al ratio of 9. The total amount of toluene adsorbed on SSZ-33 is greater as compared with MCM-68, while the later material desorbs toluene at somewhat higher temperature. Metals exchange viz. Ag+, Ag+–Co2+ and Ag+–Mn2+ on SSZ-33 and MCM-68 does not result in the increase of the amount of toluene desorbed. Hydrothermal aging does result in a significant loss of toluene adsorption on H-MCM-68 probably due to dealumination, while the adsorption capacity is reduced to a lesser extent for the high-silica zeolite H-SSZ-33.