Akademik Veri Yönetim Sistemi
Arabian Journal for Science and Engineering, cilt.48, sa.12, ss.16123-16136, 2023 (SCI-Expanded)
In this study, the effects of different types of acid treatments (H3PO4, H2SO4, and HCl) on the physicochemical properties and catalytic activity of the microporous HZSM-5 catalyst were investigated in methanol to olefins (MTO) reaction. The synthesized catalysts were characterized by XRD, N2 adsorption/desorption, ICP-MS, SEM, TEM, and pyridine-adsorbed DRIFT techniques. The characterization analyses indicated that each acid treatment led to the removal of differently positioned Al atoms in the HZSM-5 framework. Consequently, these acid treatments tuned the physicochemical properties, enhanced mesoporosity, and adjusted the Lewis Acid Site/Brønsted Acid Site (LAS/BAS) ratio of the catalysts by increasing the Si/Al ratio based on the removed Al atoms positioned in the HZSM-5 structure. In the activity tests of the catalysts, acid-treated HZSM-5 catalysts showed more stable and higher average methanol conversion, ethylene, and propylene selectivity compared to the parent catalyst. Among the acid-treated catalysts, the highest total light olefin selectivity (53%) was obtained over phosphoric acid-treated HZSM-5 due to the formation of silicoaluminophosphate-like structures, the generation of mesopores, and the adjusted acidity caused by the altered Si/Al ratio. TOS results showed that the amount of total light olefin selectivity obtained from the parent HZSM-5 was increased by 33% after phosphoric acid treatment. Acid treatments decreased coke deposition over the catalyst from 9.5 to 1.3%. Thus, it is noteworthy to say that the use of phosphoric acid-treated HZSM-5 in the MTO reaction is recommendable.