Methanol to Olefin over Ca-Modified HZSM-5 Zeolites

A series of HZSM-5 zeolites modified with Various Ca loadings were prepared by ail incipient impregnation technique and characterized by Fourier transform infrared spectra of adsorbed pyridine and temperature-programmed desorption of NH3 and CO2. Methanol to olefin (MTO) over Ca-modified HZSM-5 zeolites was performed in I flow-type fixed bed reactor. The results indicated that Ca modification increased both the catalytic stability and the light olefin selectivity, However, in excess Ca loading resulted in in inferior catalytic performance. Hence, there was ail optimal Ca loading for a specific HZSM-5, and the thus prepared Ca/HZSM-5 had little free Bronsted acid sites and presented the best catalytic performance of MTO. A possible mechanism for MTO involving acid-base centers on Ca-modified HZSM-5 zeolites has been Suggested oil the basis of the results obtained.