“…Therefore mesopore development is highly attractive to improve their catalytic performance. However, only a few studies have been reported for mesoporous TON zeolites [54][55][56][57][58][59][60][61][62]. Verboekend et al [58] demonstrated that, by using adequate conditions, desilication with NaOH yields ZSM-22 zeolites with increased mesopore surface, attributed to the presence of both intra-and inter-crystalline mesopores.…”
Section: Introductionmentioning
confidence: 99%
“…For highly siliceous ZSM-5 zeolites, tetraalkylammonium (tetrabutylammonium and tetrapropylammonium, TBA and TPA) cations can play a dominant role as pore direction agent (PDA) resulting in mesopores of small diameter and narrow size distribution [72][73][74][75][76][77][78][79]. Recently, Liu et al reported mesopore formation for ZSM-22 by extending the dissolution and recrystallization process with CTAB to the TON topology [54].…”
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.
“…Therefore mesopore development is highly attractive to improve their catalytic performance. However, only a few studies have been reported for mesoporous TON zeolites [54][55][56][57][58][59][60][61][62]. Verboekend et al [58] demonstrated that, by using adequate conditions, desilication with NaOH yields ZSM-22 zeolites with increased mesopore surface, attributed to the presence of both intra-and inter-crystalline mesopores.…”
Section: Introductionmentioning
confidence: 99%
“…For highly siliceous ZSM-5 zeolites, tetraalkylammonium (tetrabutylammonium and tetrapropylammonium, TBA and TPA) cations can play a dominant role as pore direction agent (PDA) resulting in mesopores of small diameter and narrow size distribution [72][73][74][75][76][77][78][79]. Recently, Liu et al reported mesopore formation for ZSM-22 by extending the dissolution and recrystallization process with CTAB to the TON topology [54].…”
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.
“…An excellent example was given by Konnov et al [72] who studied the hydroisomerization of n-alkanes with different chain lengths over composite supported Pt catalysts (Pt/RMOR) ( Figure 17). n-alkanes with more than six carbon atoms due to their ability to improve the metal distribution and alleviate the diffusion constraints [28,40,59,72,[100][101][102]]. An excellent example was given by Konnov et al [72] who studied the hydroisomerization of n-alkanes with different chain lengths over composite supported Pt catalysts (Pt/RMOR) ( Figure 17).…”
Micro/mesoporous zeolitic composites (MZCs) represent an important class of hierarchical zeolitic materials that have attracted increasing attention in recent years. By introducing an additional mesoporous phase interconnected with the microporosity of zeolites, a hierarchical porous system of MZCs is formed which facilitates molecular transport while preserving the intrinsic catalytic properties of zeolites. Thus, these materials offer novel perspectives for catalytic applications. Over the years, numerous synthesis strategies toward the formation of MZCs have been realized and their catalytic applications have been reported. In this review, the three main synthesis routes, namely direct synthesis using zeolite precursors, recrystallization of zeolites, and zeolitization of preformed mesoporous materials are thoroughly discussed, with focus on prior works and the most recent developments along with prominent examples given from the literature. In addition, the significant improvement in the catalytic properties of MZCs in a wide range of industrially relevant reactions is presented through several representative cases. Some perspectives for the future development of MZCs are also given.
“…Zeolites are widely used as supports due to their large specific surface area and rich pore structure. However, pure silicon zeolite is easily corroded by water, resulting in poor stability, and because of the presence of strong acid sites, the chain growth capacity of silica–alumina zeolite is decreased, leading to an increased CH 4 selectivity . Therefore, titanium silicalite (TS) zeolite with good stability and no strong acid sites can be considered as a support for FTS.…”
Titanium silicalite (TS) and TiO2 nanocomposites were prepared by mixing TS and TiO2 with different ratios in ethanol. They were impregnated with 15 wt% Co loading to afford Co‐based catalysts. Fischer–Tropsch synthesis (FTS) performance of these TS–TiO2 nanocomposite‐supported Co‐based catalysts was studied in a fixed‐bed tubular reactor. The results reveal that the Co/TS–TiO2 catalysts have better catalytic performance than Co/TS or Co/TiO2 each with a single support, showing the synergistic effect of the binary TS–TiO2 support. Among the TS–TiO2 nanocomposite‐supported Co‐based catalysts, Co/TS–TiO2‐1 presents the highest activity. These catalysts were characterized using N2 adsorption–desorption measurements, X‐ray diffraction, X‐ray photoelectron spectroscopy, H2 temperature‐programmed reduction, H2 temperature‐programmed desorption and transmission electron microscopy. It was found that the position of the active component has a significant effect on the catalytic activity. In the TS–TiO2 nanocomposites, cobalt oxides located at the new pores developed between TS and TiO2 can exhibit better catalytic activity. Also, a positive relationship is observed between Co dispersion and FTS catalytic performance for all catalysts. The catalytic activity is improved on increasing the dispersion of Co.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.