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Selective dehydration of glycerol to value-added acrolein is an interesting catalytic process not only owing to the increasing coproduction of glycerol in the biodiesel production but also due to the emerging perspectives to provide a sustainable route for acrolein production. The use of zeolites in glycerol dehydration is a very promising way with high performance, but these microporous catalysts are often severely constrained by the rapid catalyst deactivation due to coke formation. Although the introduction of hierarchical structure in microporous zeolite crystals is believed to be an effective approach to enhance their activity and lifetime, the relationship between the mesoporosity and catalytic performance is still controversial. In this paper, four kinds of typical hierarchical ZSM-5 catalysts with diverse mesoporosity and similar microporosity/acidity are prepared by the salt-aided seed-induced route. By systematically studying their catalytic performances, the effects of various mesopore types on the glycerol dehydration are declared, including pore size, amount, distribution, and connectivity. The sample with open and interconnected mesopore architecture display the high activity, long lifetime, and improved selectivity, while the worse behavior of closed and small mesopores is attributed to the mass transfer limitations and/or the in-pore condensation of reactant or its heavier derivatives. Moreover, the combined effect of acidity and hierarchical structure was also explored by changing the framework Si/Al ratio. The findings emphasize the necessity of reasonably designing the zeolite catalysts with proper hierarchical structure and acidity for maximal catalytic advantage.

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A highly stable MTP (methanol to propylene) catalyst, boronmodified hierarchical nanocrystalline ZSM-5 zeolite, has been constructed by a facile salt-aided seed-induced route. The cooperative effect of its hierarchical structure and modified acidity gives rise to a significantly stable activity (725 h) even at a high WHSV (weight hourly space velocity) of 4.0 h −1 .With the increasing demand for propylene and the decreasing stores of petroleum in a post-oil society, the methanol to propylene (MTP) process has drawn significant attention in the chemical industry. 1 Over the last two decades, much fundamental research has been conducted to develop effective catalysts with high selectivity and long lifetimes for the MTP process. 2 Recent studies have demonstrated that ZSM-5 zeolite with a high Si/Al molar ratio is one of the most promising catalysts for the MTP reaction owing to its characteristic MFI topology. 3 However, ZSM-5 zeolite still suffers from rapid/ severe deactivation associated with carbon depositions during the acid catalysed reaction process, which would result in the covering of the active sites or the blocking of the micropore channels of the catalyst, especially on the external surface. 4 In order to solve the problem of rapid/severe deactivation and develop a highly stable catalyst for the MTP reaction, abundant new strategies have been proposed. In terms of pore structure design, hierarchical structured zeolite is an ideal alternative because it possesses the advantages of both mesoporous materials and zeolite crystals with highlyimproved mass transport properties. 5 Nanocrystalline 6 and nanosheet 7 ZSM-5 with short inner diffusion paths have been adopted in several catalytic reactions to reduce the catalyst deactivation caused by pore blockage. Besides, the introduction of mesopores into the zeolite crystal during synthesis or post-synthesis modification, for example by soft templating, 8 hard templating, 9 or alkaline treatment, 10 can also slow down the deactivation of the catalysts in MTP due to their improved mass transfer properties and tolerance for a larger amount of coke. The impact of various mesopore types as well as hierarchical porosity in industrial catalysts has been proven in the recent literature. 11 Additionally, the modification of acidity and addition of some active components have also been developed with some promising results. For example, phosphorus-modified ZSM-5 has been reported with improved catalytic stability and propylene selectivity. 12 On the approach of boron isomorphous substitution, it is found that the enhanced catalytic stability can be attributed to the increase of weak acid sites. 13 The introduction of gold nanoparticles into ZSM-5 can considerably stabilize the dehydrogenation intermediates during the coking process to reinforce the catalytic stability. 14 By means of either pore structure engineering or acidity modification, the lifetime of the catalysts can be prolonged from dozens to hundreds of hours at a weight hourly space velocity (WHSV) of aroun...