Origin of Morphology Change and Effect of Crystallization Time and Si/Al Ratio during Synthesis of Zeolite ZSM‐5

Abstract

Hydrothermal synthesis of ZSM-5 is an often applied but incompletely understood procedure. In comparison to current research efforts that aim to produce complex micro-mesoporous catalysts for the conversion of biogenic and bulky hydrocarbons, this work focuses on the dependency between Si/Al ratio and zeolite morphology of microporous ZSM-5 to understand and to control the synthesis process. In two series of time dependent crystallization, kinetics were analyzed at Si/Al ratio 20 and 100 to optimize the crystallization time. Subsequently, zeolites with different Si/Al ratio were obtained and character-ized. The results show a transition from a slow dissolutionrecrystallization process to a fast solid-state-transformation with increasing Si/Al ratio. This is followed by a switching morphology from clusters of small agglomerates to bigger spherical particles. Respective acid site density and zeolite morphology determine local residence time, hydride transfer behavior and finally selectivity towards aromatics and higher hydrocarbons during methanol conversion. This background should provide control of even more complex syntheses of porous catalysts.

Low-Temperature Reforming of Biomass Tar over Ni/ZSM-5 Catalysts: Unraveling the H2-Rich Gas Production Pathways Using In Situ and Ex Situ Techniques

“…As displayed in Figure , the obtained Ni/Z catalysts (i.e., Ni/Z5, Ni/Z200, and Ni/Z80) exhibited a conventional spherical-shaped morphology . The particle size and uniformity of the three catalysts are significantly different, for example, large and agglomerated particles in Ni/Z5 gradually disappeared with the increase of the Si/Al ratio . The particles in Ni/Z200 are agglomerated into a layered structure (inconsistent with the N 2 physisorption analysis), which therefore decreased the metallic Ni surface area.…”

“…16 The particle size and uniformity of the three catalysts are significantly different, for example, large and agglomerated particles in Ni/Z5 gradually disappeared with the increase of the Si/Al ratio. 35 The particles in Ni/Z200 are agglomerated into a layered structure (inconsistent with the N 2 physisorption analysis), which therefore decreased the metallic Ni surface area. Thus, a more regular morphology and uniform particle size distribution in Ni/Z80 may show stable and efficient reactant adsorption and reaction.…”

Regulation of the Si/Al ratios and Al distributions of zeolites and their impact on properties

“…Compared to AAS, ICP-AES is especially suitable for refractory elements, such as Si and Al, which perform poorly by flame AAS. 52,112,164 However, analysis of Si and Al by AAS and ICP-AES requires the complete dissolution of zeolite samples into solution, which usually involves toxic hydrofluoric acid. This is the disadvantage of the AAS and ICP-AES.…”

“…For example, ZSM-5 (MFI-type) with Si/Al ratios ranging from 20 to 220 can be obtained by directly tuning the Si/Al ratios of the synthetic mixture in the presence of the OSDA tetrapropylammonium ions (TPA + ). 51,52 However, an unusually high concentration of Al or Si in the synthetic mixture can slow down the crystallization process, which oen requires a longer time to complete the crystallization. [53][54][55] For example, *BEA-type zeolites with Si/Al ratios from 25 to N can be synthesized from a synthetic mixture with the molar composition of 0.35Na 2 O : 4.5(TEA) 2 O : xAl 2 O 3 : 25SiO 2 : 295H 2 O, using a tetraethylammonium cation (TEA + ) as the template, where x is varied between 0 and 0.50.…”

Directing Highly a-Axis-Oriented ZSM-5 Nanosheets with Pre-estimated Bifunctional Imidazole Cations

“…The nanosheets were thickened and agglomerated at less aluminum contents, and when the Al/Si ratio was increased to more than 1/10, there was still the co-existing amorphous phase after the crystallization for 6 days. It is reasonable that large crystals were obtained in the synthetic gel with lower Al/Si ratios. , The a -oriented ZSM-5 crystals became larger and thicker with an F/Si ratio of >0.4, and when the F/Si ratio was decreased to less than 0.4, the amorphous phase was obtained as the product, emphasizing the role of fluoride as a mineralizer in adjusting the crystallization. , …”