Intercrystalline Mesopores Research Articles

Efficient synthesis of durene from syngas utilizing composite catalyst of Zr/Al activity-regulated CuZn oxides and alkali-treated HZSM-5-PEG

The one-step syngas conversion process for high-value aromatics represents a promising avenue for transforming non-petroleum resources into valuable chemicals. The utilization of Cu-based catalyst coupled with HZSM-5 enables a highly selective conversion of 1,2,4,5-tetramethylbenzene (durene). The adjustment of structure promoter Zr-Al in CuZn oxide impaired excessive hydrogenation, which solved the temperature mismatch of methanol intermediate synthesis on metal oxides and the aromatization on HZSM-5 zeolites. Multiple characterizations such as N2 adsorption and desorption, XRD, TPR/TPD, SEM-(EDS) proved that high proportion doping of zirconium greatly affected the crystal structure and morphology, which passivated the interaction of CuO/Cu with hydrogen. In addition, Polyethylene glycol modified HZSM-5 with more inter-crystalline mesopores had better diffusion performance to obtain heavy aromatics and prevent the accumulation of carbon deposits. Alkali treatment modulated the ratio of Brønsted and Lewis acids, which was favorable to specific selective alkylation for durene. The relationship between methanol space time yield and aromatic distribution was confirmed and the preferred CuZnZrAl/HZSM-5-PEG obtained CO conversion of 74.4 % with 40.6 % 1,2,4,5-tetramethylbenzene selectivity at 320 ℃ and 4.0 MPa.

Nanosized “rice ball” like hierarchical beta zeolites with inter-crystalline mesopores for efficient catalytic synthesis of lactide

A series of nanosized “rice ball” like hierarchical beta zeolite aggregates (RBZxAy, x = 6, 9, 12 or 15; y = 2, 4 or 6) with hierarchical structures are successfully synthesized via gel aging and hydrothermal method without mesoporous template. The as-prepared RBZxAy zeolites possess two ranges of inter-crystalline mesoporous that formed by zeolite nanoparticles aggregation compared to the non-aged samples (B12Z4). The effects of Si/Al ratio and crystallization time on the morphology, structure and surface acidic properties of RBZxAy were systematically investigated. Meanwhile, RBZxAy as catalysts were applied in the conversion of lactic acid (LA) to lactide (LT) to investigate their catalytic performance. Benefitting from smaller crystal size, hierarchical structures and higher acid content, the representative catalyst (RBZ12A4) exhibited outstanding catalytic activity that the LA conversion was high to 98 % and the LT yield up to 94 %. In addition, RBZ12A4 presented perfect regeneration ability after 10 times recycles. This work provides an effective and facile route to directly synthesis nanocrystals aluminosilicate zeolite with hierarchal structure, and constructs an approach for efficiently converting LA to LT, it has greatly significance for the development of polylactic acid industry.

Synthesis of hierarchical ZSM-11 and its catalytic performances during methanol to propylene

To solve the easy deactivation of zeolite catalyst in methanol to propylene (MTP) reaction, hierarchical ZSM-11 zeolite composed of loosely aggregating ultra-small nanocrystals (∼10 nm) were prepared using vinyltrimethoxysilane-methyl methacrylate (VTMS-MMA) copolymer latex as a “bond blocker”. The structure and texture properties of the as-synthesized zeolite were systematically characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption desorption, NH3-TPD, and thermogravimetric analysis (TG). The results showed that as compared with the parent ZSM-11-0 without adding the latex, the hierarchically porous ZSM-11-x (1 ≤ x ≤ 3) zeolite synthesized with VTMS-MMA copolymer latex had a higher surface area, mesopore volume, and moderate acidity. Due to the nanocrystallization of the primary grain in the polycrystalline aggregates, the micropores channels in the as-synthesized ZSM-11-x (1 ≤ x ≤ 3) were effectively shortened and abundant intercrystalline mesopores resulted from loosely aggregating of the ultrasmall primary crystals were therefore introduced, which offered the optimized ZSM-11-1 catalysts with a longer catalyst life (46 h) and a higher propylene yield (∼40.5 %) in MTP.

Fabrication of gold nanoparticles supported on hollow microsphere of nanosized TS-1 for the epoxidation of propylene with H2 and O2

The TS-1 microsphere was facilely prepared via a direct spray drying of the mixture containing the nanocrystal TS-1 and mother liquor. The calcined TS-1 zeolites possess a hollow structure and numerous intercrystalline mesopores, which may facilitate the diffusion properties. Au nanoparticles were loaded on TS-1 support by utilizing a deposition–precipitation process to prepare the Au/TS-1-M catalysts for propylene epoxidation in the presence of H2 and O2 conditions. The effects of the Ti and Au loadings on the structure, porosity, morphology, and catalytic performances of the Au/TS-1 catalysts have been investigated by various techniques. Under the optimized synthesis conditions (Si/Ti molar ratio = 57, 0.49 wt% Au), a propylene conversion of 6.1 % and a PO selectivity of 91.7 % were obtained on the Au/TS-1 catalyst. A PO formation rate of 186.8 gPO·kgcat.−1·h−1 was achieved at the 20th hour.

Mesoporous configuration effects on the physicochemical features of hierarchical ZSM-5 supported cobalt oxide as catalysts in methane partial oxidation

Hierarchical porous system has become a prevalent method to overcome the diffusion limitation of conventional zeolites. Two types of mesopores characterized as intra-crystalline (mesopores in the zeolite pore wall) and inter-crystalline mesopores (meso-sized voids between nano-zeolite aggregates) could be formed in the synthesis of hierarchical zeolites. In an attempt to investigate the influence of mesopores structure on the physicochemical properties of hierarchical ZSM-5, specifically cobalt oxide impregnated ZSM-5 zeolite samples with intra- and inter-crystalline mesopores were synthesized through two different synthesis strategies. Analysis of the physicochemical properties of the as-modified hierarchical ZSM-5 catalysts were carried out using SEM, TEM, XPS, and H2-TPR which showed distinct features given by the two mesopores configurations. Co-oxide impregnated on ZSM-5 with inter-crystalline mesopores was dominated by Co(II) species, while Co-oxide/ZSM-5 showed a fair amount of Co(III) and Co(II). Furthermore, analysis of the catalytic activity was conducted using methane partial oxidation as a model reaction. With a variation in reaction time, various types of oxygenated products, i.e. methanol, formaldehyde, formic acid, and a small trace of carbon dioxide were observed. Catalytic results suggested that the Co-oxide/ZSM-5 material with inter-crystalline mesopores configuration is more active for the methane partial oxidation reaction compared to the Co-oxide/ZSM-5 with intracrystalline mesopores. This was confirmed by the formation of formaldehyde rather than methanol as the major product in the brief reaction time of 30 min.

Facile synthesis of hierarchical NaX zeolite from natural kaolinite for efficient Knoevenagel condensation

Zeolite catalysts have found extensive applications in the synthesis of various fine chemicals. However, the micropores of zeolites impose diffusion limitations on bulky molecules, greatly reducing the catalytic efficiency. Herein, we explore an economic and environmentally friendly method for synthesizing hierarchical NaX zeolite that exhibits improved catalytic performance in the Knoevenagel condensation reaction for producing the useful fine chemical 2-cyano-3-phenylacrylate. The synthesis was achieved via a low-temperature activation of kaolinite and subsequent in-situ transformation strategy without any template or seed. Systematic characterizations reveal that the synthesized NaX zeolite has both inter-crystalline and intra-crystalline mesopores, smaller crystal size, and larger external specific surface area compared to commercial NaX zeolite. Detailed mechanism investigations show that the inter-crystalline mesopores are generated by stacking smaller crystals formed from in-situ crystallization of the depolymerized kaolinite, and the intra-crystalline mesopores are inherited from the pores in the depolymerized kaolinite. This synthesis strategy provides an energy-saving and effective way to construct hierarchical zeolites, which may gain wide applications in fine chemical manufacturing.

Acid-driven architecture of hierarchical porous ZSM–5 with high acidic quantity and its catalytic cracking performance

Controllable synthesis of ZSM–5 zeolites with hierarchical pores and high acidities is an efficient way for cracking of naphtha to produce light olefins. Here, nanocrystalline ZSM-5 aggregates (NCs) with n(Si)/n(Al) of ∼18 were hydrothermally synthesized via acid hydrolysis of a silicon source for the cracking of n–pentane. Compared with conventional microporous ZSM–5 zeolite, NCs catalysts with preserved micropores and newly generated intercrystalline mesopores promote cracking conversion as well as selectivity of light olefins. Moreover, enhanced acidities with high Al concentration in zeolite benefit the conversion of n–pentane. Interestingly, it is found that with moderate amount of framework Fe, the strength of the Brønsted acid sites of the catalysts increases and Lewis acid sites are formed in zeolite, while maintaining the total acidities. Owing to the restricted bimolecular reaction of the olefins on the adjacent acid sites, the catalysts with an Al–Fe co–framework (NC–5Al–1Fe) affords increased yield of light olefins (ethylene and propylene) up to ∼40 wt% with enhanced catalytic stability after 16 h reaction at 600 °C.

Low-temperature synthesis of three-pore system hierarchical ZSM-5 zeolite for converting palm oil to high octane green gasoline

Microporous zeolite commonly suffers from a slow diffusion rate due to its restricted micropore channel, especially for bulky molecules. In this case, hierarchical zeolite has emerged as an essential functional material because of its excellence in alleviating the diffusion issue and improving the catalytic performances. In this research, hierarchical ZSM-5 zeolite with a three-interconnected-pore system (3 PS, micro-meso-macro) has been synthesized at a low temperature (90 °C) in the presence of CaCO3 nanoparticles. The low-temperature condition leads to the formation of the highly crystalline ZSM-5 particles with intercrystalline mesopores having a pore size distribution ranging from 3 to 6 nm. Moreover, the resulting zeolites also exhibit void spaces in a macroscale (20 nm–80 nm) created from the removal of CaCO3 nanoparticles. Moreover, the catalytic tests on the catalytic cracking of palm oil demonstrate the superior activity of the trimodal porous ZSM-5 in producing high octane gasoline compared to the ZSM-5 with two pore system (2 PS), and one-pore system (1 PS). A three-interconnected-pore system enhances the accessibility of reactant molecules to and the product molecules out of the active sites within the ZSM-5 crystals. As a result, the 3 PS catalyst produces a remarkable gasoline yield (25–26%) with exceptional aromatic content (>90%) and a research octane number (RON) of 114 with a less amount of cokes deposited during the reaction. Ultimately, the 3 PS catalyst also possesses the highest stability as it can maintain the catalytic performance up to the third cycle.

Branched-chain biofuels derived from hydroisomerization of palm olein using Ni/modified beta zeolite catalysts for biojet fuel production

To overcome mass transfer limitation and adjust zeolite's acidity, the modification of beta zeolite via etching with hydrofluoric acid/ammonium fluoride (HF/NH4F) solution was revealed and the modified beta zeolite was then applied as a support of nickel (Ni) catalysts used for hydroisomerization of palm olein. HF/NH4F solution containing 0.25 M HF concentration was appropriate to enlarge original existing intercrystalline mesopores of beta zeolite (beta-0.25), which resulted to the higher pore volume. The Ni/beta-0.25 catalyst also exhibited the better Ni dispersion and lower acidity. These features suppressed overcracking and provided 43.4 wt% bio-jet fuel yield with 22.1 wt% iso-alkanes fraction when hydroisomerization was operated under 40 bar initial hydrogen (H2) pressure at 340 °C for 5 h. At 0.75 M HF concentration, the excessive leaching of aluminum species out of the zeolite framework provided beta-0.75 with very low acidity, which was ineffective to convert molecules of palm olein to bio-jet fuel range. Initial H2 pressure at 40 bar was sufficient to activate the hydroisomerization of palm olein over Ni/beta-0.25 catalyst to produce liquid biofuel containing iso−/n-alkane ratio of 2.61. The liquid biofuel/Jet A-1 blend at 50% (v/v) had freezing point and gross heating value of −58.9 °C and 43.7 MJ/kg, respectively.

Effect of Metal Complexing on Mn–Fe/TS-1 Catalysts for Selective Catalytic Reduction of NO with NH3

TS-1 zeolite with desirable pore structure, an abundance of acidic sites, and good thermal stability promising as a support for the selective catalytic reduction of NO with NH3 (NH3-SCR). Herein, a series of Mn-Fe/TS-1 catalysts have been synthesized, adopting tetraethylenepentamine (TEPA) as a metal complexing agent using the one-pot hydrothermal method. The introduced TEPA can not only increase the loading of active components but also prompts the formation of a hierarchical structure through decreasing the size of TS-1 nanocrystals to produce intercrystalline mesopores during the hydrothermal crystallization process. The optimized Mn-Fe/TS-1(R-2) catalyst shows remarkable NH3-SCR performance. Moreover, it exhibits excellent resistance to H2O and SO2 at low temperatures. The characterization results indicate that Mn-Fe/TS-1(R-2) possesses abundant surface Mn4+ and Fe2+ and chemisorbed oxygen, strong reducibility, and a high Brønsted acid amount. For comparison, Mn-Fe/TiO2 displays a narrower active temperature window due to its poor thermostability.

Aromatic compounds‐mediated synthesis of anatase‐free hierarchical TS‐1 zeolite: Exploring design strategies via machine learning and enhanced catalytic performance

AbstractSimultaneous achievement of constructing mesopores and eliminating anatase is a long‐term pursuit for enhancing the catalytic performance of TS‐1. Here, we developed an aromatic compounds‐mediated synthesis method to prepare anatase‐free and hierarchical TS‐1 for olefin epoxidation. A series of hierarchical TS‐1 zeolites were prepared by introducing aromatic compounds containing different functional groups via the crystallization process. The formation of intercrystalline mesopores and insertion of titanium into framework were facilitated at different extent. The synergistic coordination of carboxyl and hydroxyl in aromatic compounds with Ti(OH)4 realizes the uniform distribution of titanium species and eliminates the generation of anatase. Noteworthily, eight machine learning models were trained to reveal the mechanism of additive functional groups and preparation conditions on anatase formation and microstructure optimization. The prediction accuracy of most models can reach more than 80%. Benefiting from the larger mesopore volumes (0.37 cm3·g−1) and higher content of framework Ti species, TS‐DHBDC‐48h samples exhibit a higher catalytic performance than other zeolites, giving 1‐hexene conversion of 49.3% and 1,2‐epoxyhenane selectivity of 99.9%. The paper provides a facile aromatic compounds‐mediated synthesis strategy and promotes the application of machine learning toward the design and optimization of new zeolites.

Crystal Growth Blocking Strategy Enabling Efficient Solvent-Free Synthesis of Hierarchical UiO-66 for Large-Molecule Catalysis

Metal–organic frameworks (MOFs) with rich hierarchical structures have attracted great attention in processes with large molecules, such as catalysis and adsorption. However, efficiently and cost-effectively fabricating hierarchical MOFs with robust stability remains challenging. Herein, we report a crystal growth blocking strategy to prepare hierarchical UiO-66 by a solvent-free method. The addition of FeCl3 to the synthetic system blocks the overgrowth of UiO-66 crystals and limits the particle size to around just 12 nm. After the removal of Fe by ethanol treatment, these small particles loosely aggregate and gain intercrystalline mesopores. The optimal sample Mes-UiO-66 exhibits a well-developed hierarchical structure, the BET surface area reaches 1161.9 m2 g–1, and the mesopore volume attains a state-of-the-art 1.21 cm3 g–1. The superior catalytic performance and the robust stability of Mes-UiO-66 are demonstrated by the oxidation of DBT, in which the DBT conversion surpasses 99% and shows a slight decrease after five cycles. Our finding may provide a novel platform for efficiently fabricating hierarchical MOFs for large-molecule catalysis.

High accessibility to active sites of hierarchical nanocrystalline Zr-β zeolite in ethanol–acetaldehyde conversion to 1,3-butadiene

Hierarchiral β zeolites with abundant intercrystalline mesopores for improved accessibility to active sites via Silanization-based Crystallization.

A novel MOFs-induced strategy for preparing anatase-free hierarchical TS-1 zeolite:synthesis routes, growth mechanisms and enhanced catalytic performance

Titanosilicate-1 zeolites (TS-1) as one of the most commonly used catalysts for alkene epoxidation, construction of hierarchical pores as well as elimination of anatase to promote mass transportation and avoid invalid decomposition of hydrogen peroxide are always desirable yet challenging goals. Here, a novel and unique Ti-based metal organic frameworks (MOFs)-induced synthetic strategy for fabricating anatase-free hierarchical TS-1 was first proposed. All the components of MOFs perform different functions: the uniformly distributed Ti nodes replace conventional tetrabutyl titanate (TBOT) to serve as sole Ti source for constructing zeolite crystal; the separated ligands can be embedded in the zeolite framework and act as template to in situ build hierarchical pore structure; the coordination interaction between Ti nodes and ligands can efficiently avoid the anatase generation by balancing the forming rates of Ti-OH and Si-OH. This synthetic strategy is of general applicability, and two different synthetic routes including traditional hydrothermal process and steam assisted crystallization (SAC) procedure are successfully adopted. The obtained hydrothermal TS-1 and SAC anatase-free samples all possess abundant intercrystalline mesopores of 20–50 nm and even macropores between 50 and 150 nm, improving the conversion over 25 % for 1‑hexene epoxidation than TS-1 sample prepared by conventional route. The influences of the amount of Ti MOFs precursor and the crystallization process are studied in detail, and possible synthesis mechanisms are proposed. This MOFs-induced strategy might open up an avenue for the rational design of ideal and hierarchical zeolite to boost the catalytic efficiency.

Efficient conversion of glycerol to aromatics over stable nanosized x-ZF/ZM-y catalysts using ZIF-8 as a template

A series of novel nanosized x-ZF/ZM-y zeolites for glycerol to aromatics (GTA) were synthesized by using ZIF-8 as a template. The crystallization time and ZIF-8 dosage were systematically studied to clarify the crystallization process, structural characteristics and physicochemical properties of the prepared x-ZF/ZM-y. The results indicated that the growth of x-ZF/ZM-y zeolites involved two stages: attachment-impregnation and crystallization. The addition of ZIF-8 could introduce the active Zn species (ZnOH+) and induce the formation of smaller HZSM-5 nanocrystals in x-ZF/ZM-y, which could effectively facilitate the dehydrogenation-aromatization and aldol condensation steps in GTA and enhance the coke resistance. Furthermore, the ZIF-8 dosage had important influences on the catalytic performances of x-ZF/ZM-y. In particular, the 0.45-ZF/ZM-48 with 0.45 g ZIF-8 dosage and 48 h crystallization time all existed as nanocrystals of 20–40 nm, and possessed a proper redistribution of acid sites, resulting in 59.5% total aromatics yield and 11 h catalyst lifetime over 0.45-ZF/ZM-48 owing to the synergistic effect among the ZnOH+, inter-crystalline mesopores and HZSM-5 nanocrystals.

Nanosponge hierarchical micro-mesoporous MFI zeolites as a high-performance catalyst for the hydroamination of methyl acrylate with aniline

Zeolites catalyze the hydroamination of alkenes, alkynes and dienes, yielding valuable amines, enamines and imines with high efficiency and chemoselectivity (i.e., Markovnikov or anti-Markovnikov products) thanks to the architecture of their pore system and tunable acidity. However, their micropores may impose mass-transfer constraints on reaction rates. Nevertheless, the high external surface area of hierarchical micro-mesoporous zeolites should enable them to outperform conventional zeolites. To test our hypothesis, we compared the activity of hierarchical MFI zeolites of different crystal morphologies (i.e., nanosponge, nanosheet and microcrystalline desilicated samples) with that of conventional medium- (MFI) and large-pore (MOR and Beta) zeolites in the hydroamination of methyl acrylate with aniline. The results showed that nanosponge MFI had the highest activity (TOF = 32.9 h−1), reaching 57% yield of the anti-Markovnikov product N-[2-(methoxycarbonyl)ethyl]aniline. Furthermore, our kinetic study revealed a pseudo-second-order rate law with respect to aniline over the most active nanosponge MFI catalyst, with an apparent activation energy of 68.9 kJ/mol. The high external surface of this catalyst (371 m2/g) and its developed inter-crystalline mesopores (4.8 nm) suggest a kinetic-driven hydroamination reaction. Therefore, hierarchical nanosponge aluminosilicate MFI zeolites stand out as promising heterogeneous catalysts of hydroamination reactions involving bulky substrates.

Beneficial effect of steam on synthesis of hierarchically porous zeolite‐templated carbons

AbstractHierarchically meso‐/microporous carbons were synthesized using nanocrystalline beta zeolite as a sacrificial template. The zeolite template possessed intercrystalline mesopores in addition to ordered micropores of the nanocrystals. Various amounts of steam were used with a carbon source, such as ethylene, propylene or acetonitrile, to generate a carbon structure inside the template. The synthesis results showed that adding a suitable amount of steam gave rise to faithful replication of the ordered microporous structure, while the intercrystalline mesopores were retained. That is, the carbon structure was formed selectively inside nanocrystalline zeolites rather than at the exterior by the steam addition. Microscopic observation and thermogravimetric analysis revealed that steam oxidized the carbon species deposited at the external surface of zeolite nanocrystals, and hence inhibited the undesirable carbon deposition. Furthermore, such a beneficial effect of steam could be applied for the carbon synthesis using other type zeolite templates.

Transition Metal Hexacyanoferrate(II) Complexes as Catalysts in the Ring-Opening Copolymerization of CO2 and Propylene Oxide

The catalytic activity of four transition metal hexacyanoferrate(II) complexes (Ni2[Fe(CN)6], Co2[Fe(CN)6], KFe[Fe(CN)6] and Zn2[Fe(CN)6]) in the ring-opening copolymerization (ROCOP) of CO2 and propylene oxide (PO) is reported here for the first time and compared with that of other hexacyanometallate compounds. Complexes were prepared by coprecipitation employing tert-butanol as complexing agent. X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetric analysis, elemental analysis, X-ray fluorescence, scanning electron microscopy, transmission electron microscopy and N2 physisorption were used to confirm the identity of the obtained materials. Except for Zn2[Fe(CN)6], which showed an amorphous nature, the complexes were constituted by aggregates of cubic nanocrystals with intra-crystalline micropores and inter-crystalline mesopores. Gas–solid phase titration with NH3 revealed the high potential of hexacyanoferrates as Lewis acid catalysts. In the case of Zn2[Fe(CN)6], the lack of structural organization led to an extremely high density of acid sites (43 μmol m−2). The resulting copolymers were analyzed via nuclear magnetic resonance spectroscopy and gel permeation chromatography. The studied transition metal hexacyanoferrate(II) catalysts showed mild activity in the target reaction, giving rise to polyethercarbonates with moderate CO2 content (9.3–18.1 wt%), random configuration (67.0–92.4% of polyethercarbonate linkages), modest molecular weights (MW, g mol−1 = 3400–20,200) and high dispersity (ĐM = 4.0–5.4). Cyclic propylene carbonate (PC) was also produced (1.4–19.8 wt%). Among all, the Co2[Fe(CN)6] complex stands as a potential catalyst for CO2/PO ROCOP due to its high CO2 uptake, selectivity and molecular weight of the obtained copolymer.

Preparation of nanocrystalline ZSM-5 and its catalytic performance in fast pyrolysis of cellulose to produce aromatic hydrocarbons

A series of nanocrystalline ZSM-5 zeolites with abundant intercrystalline mesopores was fabricated by a hydrothermal crystallization method without any mesopore template. The ZSM-5 zeolite was characterized by XRD, XRF, N2 adsorption, NMR, SEM, TEM and NH3-TPD and used for the catalytic fast pyrolysis (CFP) of cellulose. The external surface area of the nanocrystalline ZSM-5 zeolite reached 146.6 m2/g, larger than the external surface area of conventional ZSM-5 (57.9 m2/g). The product yields of the CFP reaction were studied over different Si/Al ratios of nanocrystalline ZSM-5, and the aromatic yield of nanocrystalline ZSM-5 was generally higher than the aromatic yield of conventional ZSM-5. The relationship between the surface area, acid amounts and product yields was established by drawing a linear fitting curve. The results show that both pore structure and acidity have important effects on aromatic yield and coke yield. Aromatics are generated in micropores, and the increase in external surface area caused by reducing the particle size improves the pyrolysis of cellulose to generate bio-oil vapours, which further diffuse into micropores to generate aromatics.

Hierarchical Zeolites-confined Metal Catalysts and Their Enhanced Catalytic Performances.

The confinement of metal species within hierarchical zeolites combines the acidic/basic sites of zeolites, the enhanced mass transfer of mesoporous system, and the inside active metal sites, leading to high activity, unique selectivity, and superior stability in chemicals synthesis, energy and environment catalysis. To date, review on this emerging topic is rarely reported. Herein, we classify five metals-hierarchical zeolites composite (metal@hierarchical zeolites) according to the location of metals on hierarchical structure, including metals located on micropores, intercrystalline mesopores, intracrystalline mesopores, hollow nanobox and mesoporous shells. The synthesis and catalysis applications of metal@hierarchical zeolites composite are provided, highlighting the rational design of catalyst preparation, the improved catalytic efficiency and stability of metal species. Finally, we discuss the current limitations and future opportunities for this emerging field. This Review is expected to inspire more developments and applications of metal@hierarchical zeolites.