The Effect of Acid Strength on the Conversion of Methanol to Olefins Over Acidic Microporous Catalysts with the CHA Topology

The present work addresses the influence of acid strength on the stability and product selectivity of microporous catalysts with CHA framework type. The two studied catalysts, H-SAPO-34 and H-SSZ-13, have the same topology, density of acid sites (approximately one acid site per cage), and crystal size (0.2-2 microns), but their acid strength differ due to the framework composition. The difference in acid strength was determined by infrared spectroscopy, using CO as probe molecule. Catalytic tests were performed in a fixed bed flow reactor at 300-425 A degrees C and WHSV = 6.0 h(-1). It was observed that the acid strength has significant influence on reaction rates, enhancing the production rate of olefins in the reactor effluent as well as aromatics retained in the catalyst pores and leading to a lower optimal temperature of operation for the more acidic H-SSZ-13 catalyst. The activation and deactivation patterns and the intermediates formed are very similar for the two materials. The ethene to propene ratio increases with temperature and time on stream for both catalysts, and is higher over the more acidic H-SSZ-13 catalyst at similar reaction conditions.