Relationship between Acidity, Defective Sites, and Diffusion Properties of Nanosheet ZSM-5 and Its Catalytic Performance in the Methanol to Propylene Reaction

Abstract

A seed-induced preparation method was developed to synthesize ZSM-5 crystals, in which two different kinds of ZSM-5 crystals were used as seeds. The different preparation methods for seeds led to the difference in the morphology and Al distribution. The results showed that the synthesized zeolites showed nanosheet morphology regardless of the types of seeds. However, the different types of seed led to the difference of synthesized zeolites in the pore structure, acid properties, and defect sites. Catalytic activity for the methanol to propylene (MTP) reaction of sample synthesized from sheet-like seed was better than that synthesized from spherical seed. On the contrary, the further hydrothermal treated sample induced by spherical seed demonstrated much a longer lifetime and higher propene selectivity in the MTP reaction compared to that induced by sheet-like seed. Its excellent catalytic performance can be attributed to the proper acidity, faster diffusion rate, and fewer framework defects after hydrothermal treatment.

Structural Effects of HZSM‐5 Zeolite on Methanol‐to‐Propylene Reaction

“…3) showed that the prepared lamellar and nanosized samples have relatively more weak acid sites. Similar results have been reported by others confirming our findings [17,18]. The acidity results listed in Tab.…”

“…Xing et al reported that the catalytic lifetime of sheet-like HZSM-5 zeolite is lower than that synthesized from spherical seed which is consistent with our results [18]. By increasing the crystal size of the prepared zeolites, the diffusion path reduces and the rate of secondary reactions, such as the conversion of light olefins to aromatics, increases.…”

“…In the first step, the hydrocarbons are formed via two catalytic cycles, i.e., olefin-based and aromatic-based cycles, and the light olefins are generated by olefin conversion. According to the hydrocarbon pool theory, ethylene may be formed via the strong acid sites due to cracking of long-chain olefins and propylene and butylene formed by weaker acid sites close to the surface of HZSM-5 zeolite due to b-cleavage of carbonium ions [18,43].…”

“…Wu et al detected that the aggregation of nanosized ZSM-5 crystals decreased the defects in the zeolite structure and, as a result, the catalyst stability in MTP reaction was increased [17]. Xing et al reported that the nanosheet morphology of ZSM-5 shows excellent catalytic performance due to suitable acidity, rapid diffusion rate, and lower framework defects [18].…”

Influence of Hollow ZSM-5 Zeolites Prepared by Treatment with Different Alkalis on the Catalytic Conversion of Methanol to Aromatics

“…The acid sites, especially weak acid sites, were greatly related to defects. For zeolites, silicon hydroxyl, aluminum hydroxyl, and silanol nest were often referred to defective sites . The nature of hydroxyl groups was studied by FT-IR spectroscopy in Figure .…”