Under neutral fluoride medium at 373 K, a facile strategy has been developed to synthesise a hierarchical ZSM-5 zeolite (M-ZSM-5) using a solid silica source in a dense system. The resulting material shows a hexagonal lamellar shape with b-oriented thinner dimension and bi-modal porosity containing MFI micropores and intracrystal mesopores. The effect of synthesis factors, such as NH₄F/SiO₂, H₂O/SiO₂, crystallization temperature and time, on the zeolite morphology and size is studied and its primary crystallization process is proposed. Through varying the synthesis parameters, the crystal size could be tuned with the aspect ratio at a range of 6.2–12. Typically, M-ZSM-5 with a thinner thickness (100 nm) and a high aspect ratio (AR = 12) shows a highly effective catalytic performance in methanol to propylene (MTP) reaction. Compared to the bulk C-ZSM-5 sample obtained from a hydroxyl system, M-ZSM-5 shows higher selectivity for propylene (45.1% vs. 38.1%) and butylene (27.2% vs. 21.3%), especially prolonged catalytic lifetime (224 h vs. 98 h). This enhanced performance could be contributed to the optimized acidity and superior diffusivity of M-ZSM-5 with lamellar morphology and bimodal porosity, which are crucial for suppressing secondary reactions and inhibiting coke deposition.

Two kinds of ZSM-5 zeolites with various SiO₂/Al₂O₃ ratios were synthesized using ethanol (EtOH) or tetrapropylammonium bromide (TPABr) as the template respectively and their physicochemical properties were investigated extensively. Different ZSM-5 morphologies were observed for each kind of sample, the former with coffin-shaped single crystals and the latter with aggregates assembled from nanocrystals. The desilication process occurred and intensified at a later period of crystallization for ZSM-5 by EtOH with increasing SiO₂/Al₂O₃ ratio and/or increasing alkalinity, due to its weaker pore-filling effect. Specifically, ZSM-5 zeolites by EtOH had a large amount of Brønsted acid sites (BAS) and a much less amount of Lewis acid sites (LAS), leading to an ultra-high B/L ratio (45–66); while those by TPA⁺ with comparable acidity possessed a usual B/L ratio (6–8). Owing to no octahedrally coordinated Al in both kinds of ZSM-5, the amount of LAS should be attributed to the tri-coordinated Al “defect” sites, in accordance with the extra silanols determined by OH-IR. Further, ZSM-5 by EtOH exhibited fewer internal defective Al sites, which was responsible for its small number of LAS. Applied to n-hexane cracking, the ZSM-5 zeolite by EtOH had high activity with twice the lifetime (60 vs. 35 h) compared to that by TPA⁺ with a similar SiO₂/Al₂O₃ ratio. The ratio of accumulated amount of coke to converted n-hexane was obtained as a measure of average coke selectivity (S_c). The ZSM-5 zeolites by EtOH displayed less than half the S_c value (0.45) in comparison with those by TPA⁺ (1.08), due to the big difference in LAS, regardless of their SiO₂/Al₂O₃ ratio, morphological structure and reaction conditions. Thus, for ZSM-5 possessing a high B/L ratio improves the catalytic activity and decreases coke deposit through suppressing the dehydrogenation process of the reaction intermediate to form coke precursor.

Hierarchical porous materials especially the silica-based ones are undergoing rapid development due to potential applications in the fields of catalysis, adsorption, separation, and biomedical processes. Although various synthesis methods involving emulsions, colloids, and surfactants have been reported, synthesis of hierarchical porous silicas (HPS) with complex mesophase transformations by using a four-component microemulsion (surfactant/cosurfactant/oil/water) templating approach is still challenging. Herein, we have successfully synthesized porous silica materials by introducing n-butanol (Bu) as the cosurfactant and 1,3,5-trimethylbenzene (TMB) as the oil component in a four-component P123–n-butanol–1,3,5-trimethylbenzene–water system. By simply increasing the molar ratio of Bu to TMB continuously while keeping a fixed mass of TMB in the mean time, mesophase transformations, progressing from mesocellular foam (MCF) via a vesicle-like structure to an ordered 2D hexagonal structure (SBA-15), can be observed. Moreover, an opposite phase transformation process was also proved by gradually increasing the molar ratio of TMB to Bu by maintaining a certain value for the Bu content in the initial system. All the mixed phase silica materials including hexagonal–vesicle, MCF–vesicle–hexagonal, and MCF–disordered-SBA-15-type show hierarchically porous structures. The mechanism for the mesophase transformation was proposed and a micelle/microemulsion method with bimodal templates was put forward to form hierarchical porous silicas with a mixed phase of the MCF–disordered-SBA-15-type structure. Furthermore, a series of Al-containing mesoporous silicas with different structures (hexagonal, vesicle, MCF, MCF–vesicle–hexagonal, and MCF–disordered-SBA-15-type) were used as catalyst supports for dibenzothiophene hydrodesulfurization. The NiMo/Al-hierarchical porous silica catalyst with pore structures of MCF–disordered-SBA-15-type displayed the best hydrodesulfurization performance among all the studied catalysts.

A facile and eco-friendly approach for the synthesis of mesopore-containing ZSM-5 zeolite with small crystal size was proposed by subtly making use of a coke-deposited spent zeolite catalyst. When used in the methanol to propylene reaction again, the refabricated ZSM-5 catalyst exhibited a much higher propylene selectivity and a longer catalytic lifetime.

Herein, a specific core–shell MFI zeolite was designed for the methanol to propylene (MTP) reaction. The core–shell structure of Al-ZSM-5@B-ZSM-5 and Al-ZSM-5@silicalite-1 were easily obtained via a two-step procedure, in which Al-ZSM-5 aggregate acted as the core and B-ZSM-5 or silicalite-1 as the shell. Their core–shell structures, acidity distribution and pore properties were characterized systemically, and new insights were gained into the synergetic effect of acid property and diffusion on the MTP reaction. The Al-ZSM-5@B-ZSM-5 zeolite exhibited a superior catalytic performance with a lifetime of 350 h (WHSV = 3 h⁻¹), propylene selectivity of 49% and high turnover number of 4.3 × 10⁶, while for the Al-ZSM-5 core, the corresponding values were 210 h, 43% and 5.2 × 10⁵, respectively. Al-ZSM-5@silicalite-1 displayed the second best performance with the values of 250 h, 45% and 2.9 × 10⁶, respectively. Gradient strong acid reduction from the core to the shell via the epitaxial growth of the silicalite-1 or B-ZSM-5 shell combined with an appropriate strong/weak acid ratio plays a vital role in inhibiting the hydrogen transfer reaction and thus gives a low consumption of propylene and low coke deposition. For the hydrogen transfer reaction of alkenes to form alkanes and aromatics, strong acid sites are required. Moreover, the acid sites originally existing on the external surface of the Al-ZSM-5 core were converted into internal acid sites due to the formation of an interface zone in the core–shell zeolite, possessing micropore characteristics, which in turn improve the shape selectivity and suppress coke deposition. Especially, the Al-ZSM-5@B-ZSM-5 zeolite displayed more weak acid sites and few strong acid sites on its shell surface, which are beneficial for the low formation of external coke and also account for the highest utilization of acid sites in the MTP reaction, high propylene selectivity and long lifetime.