COADSORPTION OF TOLUENE AND METHANOL ON HZSM-5 ZEOLITES

Coadsorption of toluene and methanol on HZSM-5 at 308 and 473 K was studied to investigate adsorption complexes formed in the zeolite pores prior to alkylation reactions. Methanol is adsorbed in the form of methoxonium ions at the Si-O--Al groups of the zeolite, and toluene is hydrogen bonded to these methoxonium ions. The thermal stability of the coadsorption complex, however, is low, as concluded from temperature-programmed desorption (TPD) measurements. Toluene desorbs prior to methanol, dimethyl ether in minor amounts is the only reaction product detected in the gas phase during TPD.