Effect of simultaneous dealumination and metal incorporation of zeolite ZSM-5 on the catalytic performance in HTO process

Abstract

The hierarchical Metal Fluorinate ZSM-5 zeolites, known as M-F-Z (M: Ga, Fe, Zr, La, Ce), were modified and dealuminated through the post-synthesis method, using an NH4HF2 + metal salt mixture. The zeolites were utilized in the catalytic cracking of normal hexane to produce light olefins in high yield and propylene to ethylene ratio. A unique post-synthesis method was used in this study without any structural collapse in which a significant amount of the metal was incorporated into the zeolite framework to provide effective interactions with the acidic sites. The catalytic cracking and investigation of the performance of the prepared catalyst were carried out in a fixed-bed microreactor system. The effect of zeolite modification during the dealumination process; especially acidity changes and hierarchical factors, on the performance of the modified ZSM-5 zeolite was studied. The modified catalysts showed superior acidic properties and higher mesoporosity volume compared with the parent zeolite. XRD, ATR-FTIR, FESEM, AAS, UV–visible (DRS), BET, EDX Dot-Mapping, H2-TPR, NH3-TPD, and TGA analyses were used to determine the physicochemical properties of the modified zeolites. Based on the results, the modified Ga-F-Z zeolite, with the minimum strong to weak acidic site ratio (0.1) and the highest hierarchical factor (0.192), had the maximum light olefin production yield and propylene to ethylene ratio of 63.26% and 3.13, respectively, which is a significant improvement compared to the parent zeolite.