Abstract
The Na-ZSM-5 catalysts (SiO2/Al2O3 molar ratio = 20, 35, and 50) were prepared by rapid crystallization method to investigate their performance in butene cracking reaction. The XRD, XRF, NH3-TPD, FT-IR, TPO, UV–Vis, and 1H, 27Al, 29Si MAS NMR techniques were used to identify the physical and chemical properties of Na-ZSM-5 catalysts. The silanol group (Si–OH) was the main acid site of Na-ZSM-5, and it was proposed to be the active site for the butene cracking reaction. The butene conversion and coke formation were associated with the abundance of silanol groups over the Na-ZSM-5 catalyst. The dealumination, resulting in the deformation of tetrahedral framework aluminum species was a key factor for Na-ZSM-5 catalyst deactivation, because of the Si–O–Al bond breaking and formation of Si–O–Si bond. The stability of the Si–O–Al bond was linked to the molar number of sodium since the Na atom interacts with the Si–O–Al bond to form Si–ONa–Al structure, which enhances the stability of the silanol group. Therefore, the Si–ONa–Al in zeolite framework was an essential structure to retain the catalyst stability during the reaction. The Na-ZSM-5 with the lowest SiO2/Al2O3 molar ratio showed the best performance in this study resulting the highest propylene yield and catalyst stability.
Highlights
The Na-ZSM-5 catalysts (SiO2/Al2O3 molar ratio = 20, 35, and 50) were prepared by rapid crystallization method to investigate their performance in butene cracking reaction
The sodium content on the bulk of catalysts decreased with increasing the S iO2/Al2O3 molar ratio of Na-ZSM-5 catalyst
The acid strength and acidity number on Na-ZSM-5 catalysts with various S iO2/Al2O3 molar ratios are displayed in Fig. 1 and summarized in Supplement Table S2
Summary
The silanol group (Si–OH) was the main acid site of Na-ZSM-5, and it was proposed to be the active site for the butene cracking reaction. Previous research described the H-ZSM-5 catalyst deactivation due to coke formation during hydrocarbon cracking reaction, including coke location, coke species, and nature of coke deposition[14,15,16]. The 1H MAS NMR method is applied to identify the types of hydroxyl groups on solid catalysts, including Si–(OH)–Al, Si–OH, and Al–OH sites in z eolites[21]. The catalyst deactivation phenomena over Na-ZSM-5 (with different S iO2/Al2O3 molar ratio) during the catalytic cracking reaction of butene were studied, especially the nature of coke formation and aluminum migration over Na-ZSM-5. The nature of coke species, and coke content over the catalyst were investigated by UV–Vis, and TPO techniques, respectively
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