Control of Hierarchical Structure and Framework-Al Distribution of ZSM-5 via Adjusting Crystallization Temperature and Their Effects on Methanol Conversion

Abstract

Incorporating mesoporosity into zeolite catalysts has been regarded as an innovative technology that improves diffusivity and catalytic lifetime. Here, we propose a facile synthesis of the hierarchically structured ZSM-5 with accompanying intracrystalline mesopores, which was achieved by controlling the growth rate of the zeolite nanocrystals without using extra additives. As the crystallization temperature is strongly related to the formation of primary nanocrystals and their further growth, which fills gaps between those nanocrystals, the hierarchically structured ZSM-5 zeolite was synthesized at low crystallization temperatures (<140 °C). 27 Al MAS NMR and UV-vis-DRS analyses revealed that the hierarchically structured ZSM-5 prepared in the present study contained Al located in the straight channel at a higher proportion than the conventional microporous ZSM-5. The substitution of Al was calculated to be more difficult at the channel intersection than at other T-sites, supporting the experimental results. The hierarchically structured ZSM-5 exhibited excellent stability as well as selectivity for a methanol-to-olefin reaction. Reaction free energies calculated along the hydrocarbon pool mechanism pathway revealed that the Al located in the straight channel drives the reaction through the alkene-based cycle, which is responsible for the high olefin selectivity of the hierarchically structured ZSM-5.

Synthesis–Structure–Activity Relations in Fe-CHA for C–H Activation: Control of Al Distribution by Interzeolite Conversion

“…The divalent cation capacity (DCC) was determined by aqueous Co-exchange and ICP-AES, closely similar to the method of Dědeček et al 38 under ambient conditions to probe specific atomic configurations (proximate Al). This method, adapted by multiple authors 41,[46][47][48] studying Al distributions, uses a 0.05M Co(NO 3 ) 2 solution, starting from Na-SSZ-13. First, H + -(or partial Na + /H + )-SSZ-13 were converted to the Na +form via aqueous phase ion-exchange using 150 ml of an aqueous 0.5 M NaCl (>99% ,VWR) solution per g solids at ambient conditions under stirring.…”

Determining the Location of Co2+ in Zeolites by UV-Vis Diffuse Reflection Spectroscopy: A Critical View

“…The work of the Wichterlová group is highly recognized in the scientific community, and the developed approach to probe the Al distribution in the zeolite framework was also applied by other groups [21,22]. However, there are some doubts related to the nature of the Co sites created by ionic exchange and the assignment of the observed band triplet in the UV-Vis-DR spectra.…”

Novel One‐Step Process for the Production of Levulinic Acid from Furfural over Hierarchical Zeolites in a Microwave Reactor

“…[ 32 ] Furthermore, the Al sitting in the sinusoidal or straight channels of the ZSM‐5 significantly affects the catalytic activity. [ 33 ] Irrespective of type of pores (slit or ink bottle shaped) and extent mesoporosity, the yield of LA increased with the increase of B/L ratio ( Figure ). This indicates that the B/L ratio is a critical parameter which determines the overall activity of the catalyst.…”