Abstract
Zeolites are promising catalysts that are widely used in petrochemical, oil, and gas industries due to their unique characteristics, such as ordered microporous networks, good hydrothermal stability, large surface area, tunable acidity, and shape-selectivity. Nevertheless, the sole presence of microporous channels in zeolites inevitably restricts the diffusion of bulky reactants and products into and out of the microporous networks, leading to retarded reaction rates or catalyst deactivation. This problem can be overcome by developing hierarchical zeolites which involve mesoporous and macroporous networks. The meso- and macro-porosities can enhance the mass transport of molecules and simultaneously maintain the intrinsic shape selectivity of zeolite microporosity. Hierarchical zeolites are mainly developed through post-synthesis and pre-synthesis or in situ modification of zeolites. In this review, we evaluated both pre-synthesis and post-synthesis modification strategies with more focus on post-synthesis modification strategies. The role of various synthesis strategies on the intrinsic properties of hierarchical zeolites is discussed. The catalytic performance of hierarchical zeolites in important biomass reactions, such as catalytic pyrolysis of biomass feedstock and upgradation of bio-oil, has been summarized. The utilization of hierarchical zeolites tends to give a higher aromatic yield than conventional zeolites with microporosity solely.
Highlights
Zeolites are hydrated aluminosilicates with an ordered framework, which offers mechanical and thermal stability to zeolites [1]
Biomass conversion via catalytic pyrolysis and bio-oil upgradation using zeolite catalysts are among the emerging processes that have attracted significant interest in recent years
The secondary porosity introduced in hierarchical zeolites offers improved catalytic performance, which is mainly attributed to diffusion with no impediment, of large compounds into the active sites present inside the channels
Summary
Zeolites are hydrated aluminosilicates with an ordered framework, which offers mechanical and thermal stability to zeolites [1]. A review on hierarchical zeolites and its catalytic applications has of hierarchical zeolites as a whole or on specific aspects, such as using hierarchical zeolites as catalysts been published by Feliczak-Guzik [12] All these articles mainly discuss the significance of hierarchical for certain reactions. Been published by Feliczak-Guzik [12] All these articles mainly discuss the significance of reviewed the synthesis strategies and later discussed the application of hierarchical zeolites for two hierarchical zeolites from various perspectives. Considering catalytic biomass conversion is an emerging research area and its significance has attracted enormous interest from industry, this review article aims at exploring the methods of preparing hierarchical zeolites and their potential applications in catalytic pyrolysis and bio-oil upgradation
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