Insights into NH4-SAPO-34 preparation procedure: Effect of the number of ammonium exchange times on catalytic performance of Zn-modified SAPO-34 zeolite for methanol to olefin reaction

Abstract

Abstract Zn-modified SAPO-34 zeolites via NH4-SAPO-34 intermediates were prepared, and the effect of the number of ammonium exchange times on their catalytic performance in methanol to olefin (MTO) reaction was comprehensively investigated. The physicochemical properties of parent and Zn-modified SAPO-34 zeolites were characterized by XRD, SEM, N2 adsorption-desorption, NH3-TPD, XRF, XPS and TGA. The reaction results show that the catalytic lifetime and product selectivity of Zn-modified SAPO-34 zeolites is closely related to the number of ammonium exchange times, and the samples with more than two times of ammonium exchange exhibit excellent catalytic performance in MTO reaction with ca. 50 C-% of ethene selectivity, ca. 75 C-% of light olefins selectivity and ca. 2.0 of ethene to propene ratio. Besides, the effect of the number of ammonium exchange times on the structural integrity and the location of the introduced Zn-related species of Zn-modified SAPO-34 zeolites is described.