Seed-Assisted Synthesis of ZSM-5 Aggregates Assembled from Regularly Stacked Nanosheets and Their Performance in n-Hexane Aromatization

Abstract

HZSM-5 crystals with short straight channels possess the advantages of easier diffusion and less coke formation in petrochemical processes. In this work, aggregated ZSM-5 zeolite assembled by regularly stacked nanosheet-like crystals with a b-axis thickness of 60 nm was synthesized using specially designed silicate-1 as seed. Silicate-1 (S-2) was synthesized using relatively lower cost silica sol as a silica source, tetrapropylammonium bromide (TPABr) as a structure-directing agent (SDA), and ethylamine as an assistant compared with traditional silicate-1 (S-1: tetraethyl orthosilicate (TEOS) as a silica source and tetrapropylammonium hydroxide (TPAOH) as an SDA). When S-2 seeds were added into the synthesis system, the seeds could limit the crystal growth along the b-axis direction under the assistance of ethylamine. Meanwhile, the adjacent ZSM-5 nanosheet crystals would spontaneously stack together. The catalyst Zn/S-2-1 exhibited relatively higher n-hexane conversion and selectivity of benzene, toluene, ethylbenzene, and xylene (BTEX) as well as catalytic stability in contrast to the catalyst synthesized using S-1 as seed when being used in the n-hexane aromatization reaction. This work opened up a new prospective for ZSM-5 aggregates assembled from the nanosheet catalyst design in the application of hydrocarbon aromatization.

Alcohol‐Assisted Synthesis of Sheet‐Like ZSM‐5 Zeolites with Controllable Aspect Ratios

“…On the one hand, the S‐ZSM‐5 with larger surface area could expose more active sites. Moreover, a faster diffusion of the reactants would promote their access to the active sites due to a thinner b‐axis [33–34] . In terms of product selectivity, as shown in Figure 8c and 8d, the S‐ZSM‐5 catalyst demonstrates the slightly higher ethylbenzene selectivity (ca.…”

Synthesis of Two-Dimensional Zeolite Nanosheets Applied to the Catalytic Cracking of a Waste Cooking Oil Model Compound to Produce Light Olefins

“…The mass loss throughout the range of 200–800 °C was attributed to the oxidation of deposited coke (specifically, to soft carbon in the range of 200–400 °C and hard carbon in the range of 400–800 °C). 45 , 46 The two catalysts evidently differed in coke content because the CZSM-5 zeolite showed a mass loss of 19.4% after removing all coke deposits, whereas the HNZSM-5 had a mass loss of 27.1%. More coke was deposited on the latter material because this specimen had more accessible acid sites, and the formation of carbonaceous species is promoted by the large number of acidic sites on the outer surfaces.…”

Anisotropic ZSM-5 nanorod assemblies: facile synthesis, epitaxial growth, and strikingly enhanced stability in benzene alkylation

“…It is widely reported that the number of strong acid sites plays a dominant role in some reactions including oligomerization, isomerization, cracking and aromatization. 18,[46][47][48][49][50][51]57,58 Hence, the density of acid sites on different samples is quantified and compared. As shown in Table 2, a decrease in the total acid sites can be obviously observed with the introduction of CTAB into the synthesis gel, which should be ascribed to the decrease in the Al content in NA-ZSM-5 x .…”