Generalized synthesis of core–shell structured nano-zeolite@ordered mesoporous silica composites

Gradient Hierarchically Porous Structure for Rapid Capillary-Assisted Catalysis

Synthesis of hierarchically porous structures with uniform spatial gradient and structure reinforcement effect still remains a great challenge. Herein, we report the synthesis of zeolite@mesoporous silica core-shell nanospheres (ZeoA@MesoS) with a gradient porous structure through a micellar dynamic assembly strategy. In this case, we find that the size of composite micelles can be dynamically changed with the increase of swelling agents, which in situ act as the building blocks for the modular assembly of gradient mesostructures. The ZeoA@MesoS nanospheres are highly dispersed in solvents with uniform micropores in the inner core and a gradient tubular mesopore shell. As a nanoreactor, such hierarchically gradient porous structures enable the capillary-directed fast mass transfer from the solutions to inner active sites. As a result, the ZeoA@MesoS catalysts deliver a fabulous catalytic yield of ∼75% on the esterification of long-chain carboxylic palmitic acids and high stability even toward water interference, which can be well trapped by the ZeoA core, pushing forward the chemical equilibrium. Moreover, a very remarkable catalytic conversion on the C-H arylation reaction of large N-methylindole is achieved (∼98%) by a Pd-immobilized ZeoA@MesoS catalyst. The water tolerance feature gives a notable enhancement of 26% in catalytic yield compared to the Pd-dendritic mesoporous silica without the zeolite core.

Zeolites and Related Materials as Catalyst Supports for Hydrocarbon Oxidation Reactions

Catalytic oxidation is a key technology for the conversion of petroleum-based feedstocks into useful chemicals (e.g., adipic acid, caprolactam, glycols, acrylates, and vinyl acetate) since this chemical transformation is always involved in synthesis processes. Millions of tons of these compounds are annually produced worldwide and find applications in all areas of chemical industries, ranging from pharmaceutical to large-scale commodities. The traditional industrial methods to produce large amounts of those compounds involve over-stoichiometric quantities of toxic inorganic reactants and homogeneous catalysts that operate at high temperature, originating large amounts of effluents, often leading to expensive downstream processes, along with nonrecovery of valuable catalysts that are loss within the reactant effluent. Due to the increasingly stringent environmental legislation nowadays, there is considerable pressure to replace these antiquate technologies, focusing on heterogeneous catalysts that can operate under mild reactions conditions, easily recovered, and reused. Parallelly, recent advances in the synthesis and characterization of metal complexes and metal clusters on support surfaces have brought new insights to catalysis and highlight ways to systematic catalysts design. This review aims to provide a comprehensive bibliographic examination over the last 10 years on the development of heterogeneous catalysts, i.e., organometallic complexes or metal clusters immobilized in distinct inorganic supports such as zeolites, hierarchical zeolites, silicas, and clays. The methodologies used to prepare and/or modify the supports are critically reviewed, as well as the methods used for the immobilization of the active species. The applications of the heterogenized catalysts are presented, and some case-studies are discussed in detail.

Effect of two-component amorphous silica-alumina (ASA) with different Si/Al molar ratios on hydrocracking reactions for increasing naphtha over NiW/USY-ASA

The combination of ASA-0.4 and ASA-2 produces new acidic OH groups by increasing the contact points between silicon and aluminum. These OH groups improve the density of acid sites and increases the area of the active adsorption area of the support.

Regulation mechanism of three key parameters on catalytic characterization of molybdenum modified bimetallic micro-mesoporous catalysts during catalytic fast pyrolysis of enzymatic hydrolysis lignin

Novel preparation of molybdenum modified bimetallic micro-mesoporous catalyst was proposed innovatively to conduct catalytic fast pyrolysis of enzymatic hydrolysis lignin. The optimal catalytic characterization of the prepared catalyst was attributed to appropriate porous structure, the interaction between zeolite support and metal species, and the synergetic and stable mechanism of bimetallic active sites. With the incorporation of metal species into micro-mesoporous catalyst, the distribution of active sites experienced a regulation, which contributed to MAHs production and cracking of oxygen-containing substances. NiMo/AZM catalyst exhibited the most obvious coke inhibition effect (8.47 wt% of mass yield) and converted more high-ordered graphite carbon to low-ordered one, so as to make it easier to remove and prolong the catalyst lifetime, and obtained the highest mass yield of MAHs (13.15 wt%) as well as the minimum selectivity of bulky oxygenates (3.82%), which was the joint contribution of three key parameters.

Tailoring hierarchical zeolite composites with two distinct frameworks for fine-tuning the product distribution in benzene alkylation with ethanol

A hierarchical zeolite composite, MOR@ZSM-5, with two distinct frameworks has been successfully fabricated via the repeated crystallization of ZSM-5 nanocrystals on mordenite surfaces. To avoid their phase separation, the surface of mordenite was pretreated with tetra(n-butyl)ammonium hydroxide (TBAOH) to induce the formation of the ZSM-5 nuclei, and it was subsequently modified by the continuous growth of nanocrystalline ZSM-5 on the entire area of the mordenite surfaces. Interestingly, the fully overgrown MOR@ZSM-5 composite exhibits a remarkable improvement in the ethylbenzene selectivity (>60%) obtained from the alkylation of benzene with ethanol with respect to isolated zeolites and their physical mixture due to the enhanced external surface area and hierarchical porosity as well as the reasonable acidity provided by the fully dispersed ZSM-5 nanocrystals on the mordenite surfaces. Moreover, coke species deposited on the designed composites are likely located at the external surfaces and do not considerably deteriorate the catalytic performance, whereas they are deposited predominantly in the micropores over the incompletely overgrown MOR@ZSM-5 composite. The present study illustrates the advantages of the overgrown zeolite composites of two incompatible frameworks in tailoring the hierarchical porosity, adjusting the acidic properties, and eventually controlling the product selectivity in acid-catalyzed reactions such as the alkylation of benzene with ethanol.

Rational Design of Yolk-Shell CuO/Silicalite-1@mSiO2 Composites for a High-Performance Nonenzymatic Glucose Biosensor

In this study, an interface coassembly strategy is employed to rationally synthesize a yolk-shell CuO/silicalite-1@void@mSiO₂ composite consisting of silicalite-1 supported CuO nanoparticles confined in the hollow space of mesoporous silica, and the obtained composite materials were used as a novel nonenzymatic biosensor for highly sensitive and selective detecting glucose with excellent anti-interference ability. The synthesis of CuO/silicalite-1@mSiO₂ includes four steps: coating silicalite-1 particles with resorcinol-formaldehyde polymer (RF), immobilization of copper species, interface deposition of a mesoporous silica layer, and final calcination in air to decompose RF and form CuO nanoparticles. The unique hierarchical porous structure with mesopores and micropores is beneficial to selectively enrich glucose for fast oxidation into gluconic acid. Besides, the mesopores in the silica shell can effectively inhibit the large interfering substances or biomacromolecules diffusing into the void as well as the loss of CuO nanoparticles. The hollow chamber inside serves as a nanoreactor for glucose oxidation catalyzed by the active CuO nanoparticles, which are spatially accessible for glucose molecules. The nonenzymatic glucose biosensors based on CuO/silicalite-1@mSiO₂ materials show excellent electrocatalytic sensing performance with a wide linear range (5-500 μM), high sensitivity (5.5 μA·mM^-1·cm^-2), low detection limit (0.17 μM), and high selectivity against interfering species. Furthermore, the unique sensors even display a good capability in the determination of glucose in real blood serum samples.

Hierarchy concepts: classification and preparation strategies for zeolite containing materials with hierarchical porosity

Starting from a basic classification of “hierarchical porosity” this review gives a broad overview of preparation routes towards hierarchically porous all-zeolite and zeolite containing composite materials.

Bulk and composite catalysts combining BEA topology and mesoporosity for the valorisation of furfural

Synthesis strategies to materials integrating BEA topology, Zr,Al-sites and mesoporosity, for furfural valorisation via integrated reduction/acid reactions in an alcohol medium.

Hierarchical ZSM-11 zeolite prepared by alkaline treatment with mixed solution of NaOH and CTAB: characterization and application for alkylation of benzene with dimethyl ether

The composite effects of NaOH and CTAB regulated the porosity and acidity of ZSM-11 samples, which affected the reaction stability.

Synthesis of core–shell ZSM-5@meso-SAPO-34 composite and its application in methanol to aromatics

A core/shell-structured ZSM-5@meso-SAPO-34 composite catalyst was hydrothermally synthesized through overgrowing SAPO-34 molecular sieve on the external surface of ZSM-5.

Enhanced performance in NOx reduction by NH3 over a mesoporous Ce–Ti–MoOx catalyst stabilized by a carbon template

The mesopore Ce–Ti–MoO_x catalyst stabilized by an in situ formed carbon template showed more than 90% NO_x conversion at 175–425 °C for SCR of NO_x with NH₃. Increasing temperature in the presence of carbon template contributed to the narrow mesoporous distribution and excellent low-temperature SCR activity.

Preparation of hierarchically structured Y zeolite with low Si/Al ratio and its applications in acetalization reactions

Hierarchically structured Y zeolites were prepared by a post-synthetic strategy, where the as-made NaY zeolite was sequentially treated by a lactic acid solution and an alkaline solution containing cetyltrimethyl ammonium bromide (CTAB).

Site-specific carbon deposition for hierarchically ordered core/shell-structured graphitic carbon with remarkable electrochemical performance

A fascinating core-shell-structured graphitic carbon material composed of ordered microporous core and uniform mesoporous shell is fabricated for the first time through a site-specific chemical vapor deposition process by using a nanozeolite@mesostructured silica composite molecular sieve as the template. The mesostructure-directing agent cetyltrimethylammonium bromide in the shell of the template can be either burned off or carbonized so that it is successfully utilized as a pore switch to turn the shell of the template "on" or "off" to allow selective carbon deposition. The preferred carbon deposition process can be performed only in the inner microporous zeolite cores or just within the outer mesoporous shells, resulting in a zeolite-like ordered microporous carbon or a hollow mesoporous carbon. Full carbon deposition in the template leads to the new core-shell-structured microporous@mesoporous carbon with a nanographene-constructed framework for fast electron transport, a microporous nanocore with large surface area for high-capacity storage of lithium ions, a mesoporous shell with highly opened mesopores as a transport layer for lithium ions and electron channels to access inner cores. The ordered micropores are protected by the mesoporous shell, avoiding pore blockage as the formation of solid electrolyte interphase layers. Such a unique core-shell-structured microporous@mesoporous carbon material represents a newly established lithium ion storage model, demonstrating high reversible energy storage, excellent rate capability, and long cyclic stability.