Synthesis, characterisation, and catalytic evaluation of hierarchical faujasite zeolites: milestones, challenges, and future directions

Abstract

Faujasite (X, Y, and USY) zeolites represent one of the most widely-applied and abundant catalysts and sorbents in the chemical industry. In the last 5 years substantial progress was made in the synthesis, characterisation, and catalytic exploitation of hierarchically-structured variants of these zeolites. Hererin, we provide an overview of these contributions, highlighting the main advancements regarding the evaluation of the nature and functionality of introduced secondary porosity. The novelty, efficiency, versatility, and sustainability of the reported bottom-up and (predominately) top-down strategies are discussed. The crucial role of the relative stability of faujasites in aqueous media is highlighted. The interplay between the physico-chemical properties of the hierarchical zeolites and their use in petrochemical and biomass-related catalytic processes is assessed.

Quantifying the Complex Pore Architecture of Hierarchical Faujasite Zeolites and the Impact on Diffusion

“…The moderate amount of mesopores developed in the steam-treated CBV500 comprises primarily (>90%) occluded or constricted. In line with additional TEM evidence ( Figure S4, Supporting information), it appears that the channel-like structures that develop within this sample are significantly blocked by the extraframework debris known to result from the treatment, [3,20] while the cavity-like mesopores can be envisaged to have constricted geometry. Mild acid treatment (CBV712) moderately enhances the fraction and amount of pyramidal mesopores, which have varying sizes (d meso = 3-20 nm, d win = 3-20 nm), as observed in the contour plot ( Figure 5).…”

“…[3] Pore volumes and average pore sizes are readily quantified by routinely available adsorption and porosimetry methods. On the other hand, the characterization of the mesopore distribution, encompassing the geometry, location, and connectivity, at the nanoscale presents many challenges.…”

Micro/Mesoporous Zeolitic Composites: Recent Developments in Synthesis and Catalytic Applications

“…3 and 4) is probably an artefact. It was outlined by Groen et al [25,26] that a peak with mean pore radius at around 10 Å , observed in pore radius distributions of ZSM-5 obtained from nitrogen isotherms by the BJH method [19], is caused by phase transition (solidification) of the nitrogen adsorbed in the ZSM-5 micropores and not by the presence of real mesopores. Fig.…”

“…In recent years, there has been a rapid development in synthesis and applications of hierarchical zeolitic materials. Many excellent reviews highlighting various aspects of the latest progress in this field have been published [6,[8][9][10]13,14,[16][17][18][19][20][21][22][23][24][25][26][27][28][29]. It should be noted that most of them have focused on hierarchical zeolites (HZs).…”

A Hierarchically Micro-Meso-Macroporous Zeolite CaA for Methanol Conversion to Dimethyl Ether

“…It is well-known that the incorporation of additional meso(macro)pores in zeolite can enhance the accessibility to the active sites, overcoming the steric limitations and shortening diffusion pathways. Hence, as the optimal solution, the synthesis of hierarchically structured zeolitic materials with two or three levels of porosities in zeolite has obtained intensive attention [7][8][9][10][11][12][13][14][15]. Compared with other zeolites, there are fewer reports on the synthesis of hierarchically structured zeolites LTA, either by using organosilane surfactants such as 3-(trimethoxysilyl)propyl hexadecyl dimethyl ammonium chloride (TPHAC) as a soft-template [16], by amino acid as a mesopore generating agent [17], or by using organofunctionalized silica as an Si-source, which was reported by our research group [18].…”