Abstract: The acid properties of BEA/MOR (intergrowth of zeolite β and mordenite) samples with SiO2/Al2O3 molar ratio of 25 were characterized by temperature-programmed desorption of NH3 (NH3-TPD). There is a volcano-type relationship between the higher NH3-TPD peak temperature and the mordenite content of the BEA/MOR samples, and the NH3-TPD peak temperature reached the maximum at mordenite content of about 65%. In contrast, there is a linear relationship between the higher NH3-TPD peak temperature and the mordenite content of the mechanical mixtures of zeolite β and mordenite. No obvious difference in the acid strength existed between the BEA/MOR samples and the mechanical mixtures when the mordenite content was less than 50%. However, when the mordenite content exceeded 50%, the BEA/MOR samples possessed much higher acid strength than the mechanical mixtures. The BEA/MOR sample with 65% mordenite showed the highest acid strength, which was higher than that of the mordenite. The catalytic activity measurements of all the samples for methanol dehydration were carried out in a fixed-bed reactor under atmospheric pressure, temperature of 180 ℃, and methanol space velocity of 2 h-1. Dimethyl ether and water were the only products for each catalyst. No coke formation and catalyst deactivation were observed in the reaction of 6 h. There is a linear relationship between the methanol conversion and the mordenite content of the mechanical mixtures. The BEA/MOR samples with mordenite content higher than 40% showed higher catalytic activity than HM, and the BEA/MOR with 65% mordenite showed the highest methanol conversion. The catalytic activity of BEA/MOR also exhibited a volcano-type behavior. Compared with the mechanical mixtures, the BEA/MOR samples displayed higher catalytic activity. The HM with SiO2/Al2O3 molar ratio of 11 deactivated after 60 h reaction though it had high initial activity. The HBEA/MOR with SiO2/Al2O3 molar ratio of 53 showed relatively high catalytic activity and stability.

Key words: molecular sieve, zeolite β, mordenite, intergrowth, acidity, ammonia, temperature-programmed desorption, methanol dehydration, dimethyl ether