Influence of post-synthetic modifications on the composition, acidity and textural properties of ZSM-22 zeolite

Abstract

In this work, an extensive investigation of the preparation of a large body of desilicated ZSM-22 zeolites and their basic characterization is presented. We investigate the effects of the properties of the starting zeolite, and we employ mixtures of NaOH with CTAB or TBAOH as well as subsequent acid washings to create mesoporous zeolites. Scanning and transmission microscopy and nitrogen adsorption revealed that the crystal morphology of the starting zeolite appears to be the dominant parameter which influences the mesopore generation. Mesopores were effectively created within the rodlike commercial crystallites, whereas the thinner dimensions of the needle-shaped particles of the in house prepared zeolite represent an obstacle for an intra-mesopore creation. The alkaline, surfactant-assisted or combined NaOH/TBAOH desilication methods resulted in mesopores with different shape and size from the commercial 2 zeolite. The sequential acid washing generally resulted in increased the micropore volume with respect to the desilicated samples. Elemental analysis showed that extraframework Al species were generated upon the desilication treatments, which are eventually removed by the acid treatment. The acidity studied by FTIR demonstrated that this occurs without a marked modification of the Brønsted acidity, whereas the concentration of surface silanol hydroxyl groups is increased. The comparison between the total Al concentration and the amount of Al in acidic sites shows that the acidity was recovered after the acid washing and suggests that original non-acidic Al species in the starting materials may have a role in the formation of both Lewis and extra-framework species upon desilication.

Tuning the material and catalytic properties of SUZ-4 zeolites for the conversion of methanol or methane

“…Note also the decreasing peak at 2.3 ppm corresponding to Al-OH groups, which can be explained by a decreased total quantity of EFAl (in accordance with the aluminum content by EDX) and/or condensation of EFAl Al-OH groups to the oxide. Both observations are in agreement with observations made for desilicated ZSM-22 zeolites [16,17]. FT-IR spectra of characteristic SUZ-4 catalysts are shown in Fig.…”

“…For S1Na, the overall ASD decreases significantly. A similar decrease in ASD is observed on other 1-dimensional 10-MR pore catalysts like ZSM-22 [16,17]. As on ZSM-22, this is on SUZ-4 accompanied by an increased amount of Si-OH groups and a higher water content as a result of the desilication.…”

“…As post-modifications, alkaline and/or acid treatment is applied in different severity to remove deposits and to dealuminate the zeolite. Similar techniques have led to reduced ASD for the comparable zeolite Ferrierite [14,15], and to significant improvements in the performance of unidimensional ZSM-22 catalysts [16,17].…”

State of the Art and Perspectives of Hierarchical Zeolites: Practical Overview of Synthesis Methods and Use in Catalysis

“…The Brønsted acidity of the zeolite did not seem to be modified because of desilication, although the amount of surface hydroxyls decreased. [40] The different hierarchical ZSM-22 zeolites of del Campo et al were tested in the MTH conversion. The obtained results indicated that the catalyst lifetime could be increased dramatically when using a hierarchical ZSM-22.…”

Hierarchical MTW zeolites in tetrahydropyranylation of alcohols: Comparison of bottom-up and top-down methods

“…This approach has been well investigated on one of the most commercially applied zeolite, MFI [16,18]. Unfortunately, the data for other zeolite topologies desilicated in the presence of TAA + are scarce [25,26]. Hence, our goal is to examine the influence of desilication with TAA + solutions on the MTW topology.…”