Full Compositional Flexibility in the Preparation of Mesoporous MFI Zeolites by Desilication

Abstract

We demonstrate that desilication in alkaline medium is a suitable post-synthetic method to introduce intracrystalline mesoporosity in MFI zeolites independent of the Si/Al ratio in the parent material. By systematic screening of the influence of both base concentration (0.1-1.8 M NaOH) and Si/Al ratio (10-1000) on the properties of the treated zeolites, we reveal that effective mesoporosity introduction Hierarchical ZSM-5 after acid washing stands as the most active sample, which stresses the relevance of the additional post-synthesis treatment step.

Catalytic cracking performance of alkaline-treated zeolite Beta in the terms of acid sites properties and their accessibility

“…controlled silicon extraction from the zeolite framework in alkaline aqueous solution has been developed as one of the most efficient methods to design microand mesoporous (hierarchical) zeolites [4,5]. The desired intracrystalline mesoporosity is ruled by the interplay of micro-and mesopores and is, however, influenced by the value of the framework Si/Al ratio [6,7]. It has been reported that aluminium atoms in framework positions play a crucial role in silicon extraction directing the mesopore formation process, as the AlO4 -tetrahedra are reported to protect Si atoms in the neighbourhood against OH -ions attack due to electrical repulsion [8].…”

The Role of Non-Framework Lewis Acidic Al Species of Alkali-Treated HZSM-5 in Methanol Aromatization

“…The improved hydride transfer and methylation/transalkylation activities were discovered on alkali-treated HZSM-5, whereas such an enhancement was absent in its amorphous Al-extracted counterpart. [22]. In order to extract non-framework Al, alkali-treated ZSM-5 was subjected to an acid treatment with 0.1 M aqueous HCl at 65 • C for 6 h [22].…”

“…[22]. In order to extract non-framework Al, alkali-treated ZSM-5 was subjected to an acid treatment with 0.1 M aqueous HCl at 65 • C for 6 h [22]. All catalysts were subsequently transformed into H + form via the ion exchange method [28] before any test.…”

“…A more than two-fold increase of Al(Oh) (from 10% to 23%) and a substantial decrease of Al(Td) (from 90% to 77%) were observed on HZ-D. This variation indicates the presence of alkaline-induced Lewis acidic Al species on the outer surface [22]. As for HZ-DA, Al(Td) seemed to grow back from 77% to 87% with Al(Oh) that decreased from 23% to 13%.…”

“…inspection showed that HZ-D had the mesopore size at 11.5 nm; HZ-DA, 18.7 nm. The difference in the mesopore size of HZ-D and HZ-DA is related to the removal of amorphous Al debris by acid wash [22], that can reopen partially occluded mesopores. Indeed, compared to HZ-D and parent HZSM-5 (HZ), higher mesoporosity of HZ-DA should have lower mass transport resistance.…”