Interconnected Mesopores Research Articles

Effect of weak base modification on ZSM‐5 catalyst for methanol to aromatics

The effect of weak base modification on the catalytic performance of ZSM‐5 catalyst for conversion of methanol to aromatics was investigated. The catalysts were characterized using X‐ray diffraction, X‐ray fluorescence, N2 adsorption–desorption, NH3 temperature‐programmed desorption, Fourier transform infrared spectroscopy, scanning electron microscopy and thermogravimetry. The results showed that catalysts treated with weak base (NaHCO3, Na2CO3 and NH3⋅H2O) exhibited a pore structure with interconnected micropores and mesopores. The existence of mesopores was beneficial for improving the diffusion of reactants and products, and the coke deposition resistance capacity of treated catalysts was enhanced greatly. Meanwhile, compared to traditional ZSM‐5 zeolite, the ratio of Brønsted to Lewis (B/L) acid sites of ZSM‐5/NH3⋅H2O (B/L = 7.35) zeolite slightly increased but the amount of acid sites reduced, while those of ZSM‐5/NaHCO3 (B/L = 0.127) and ZSM‐5/Na2CO3 (B/L = 0.107) significantly reduced. Further, the catalyst treated with NH3⋅H2O solution was evaluated in the methanol to aromatics reaction and led to an enhanced aromatization reaction rate. The liquid hydrocarbons product distribution exhibited higher aromatic hydrocarbons yield (56.12%) and selectivity (40.28%) of benzene, toluene and xylene (BTX) with isoparaffin content reducing to 26.17%, which could be explained by appropriate B/L acid sites ratio, higher pore volumes and higher surface area.

Sponge-Like Porous Manganese(II,III) Oxide as a Highly Efficient Cathode Material for Rechargeable Magnesium Ion Batteries

Here, we are the first to report a spinel type Mn3O4 as cathode material for Mg-ion battery (MIB) with graphite foil (Gif) as current collector. High Coulombic efficiency and good cyclic stability of Mn3O4 are demonstrated, and the process is enhanced by using Mn3O4 nanoparticles with a sponge-like morphology. The powder exhibits a network of interconnected mesopores with well-dispersed nanoparticles (∼10 nm) and large specific surface area (102 m2 g–1). This structural configuration provides easy access for electrolyte penetration which markedly enhances the utilization of electroactive material, generates high ion flux across the electrode–electrolyte interface and provides more active sites for electrochemical reactions to occur. This study can possibly open the way for exploring other similar compounds with a spinel type structure for MIB.

Super-adsorbent material based on functional polymer particles with a multilevel porous structure

Porous polymer particles with multilevel structures consisting of submicron-sized hollow cavities and interconnected mesopores within the crosslinked shell were designed and prepared. An extremely high density of anhydride groups in the crosslinked shell can be conveniently converted into versatile functional groups for the adsorption of hazardous pollutants. As a proof of concept, we utilized carboxylate-functionalized hollow particles as a selective adsorbent for the removal of the basic dye methylene blue and found that these particles exhibited a very high adsorption capacity (1603 mg g−1). Furthermore, the hollow structure, highly interconnected mesopores and rigid shell of the particles not only endow the adsorbent with fast adsorption/desorption rates but also facilitate their facile separation and easy regeneration. We believe that these porous polymer particles have great potential for applications in many fields, including as adsorbents, catalyst supports and matrices for the binding of sensitive materials. Submicron porous polymer particles with a multilevel structure can adsorb more than 1.5 times their own weight of dye. Super-adsorbent materials are needed for removing pollutants from contaminated water among other applications. Now, Wantai Yang of Beijing University of Chemical Technology in China and co-workers have produced particles that have hollow cores, a network of pores in their shells, and three-dimensional networks formed by cross-linking. The combination of this multilevel structure and their extremely high density of anhydride groups make the particles ideal for mopping up pollutants. The researchers demonstrated the particles' potential by achieving an adsorption capacity of 1,603 milligrams per gram for the dye methylene blue. As well as finding application as adsorbents for heavy-metal ions, these particles could be used as a catalyst support and a matrix for binding sensitive materials. Multilevel structured porous polymer particles, consisting of submicron hollow cavities and crosslinked shell with interconnected mesopores, are specially designed, prepared and served as super-adsorbent materials. As a proof of concept, we applied the carboxylate-functionalized hollow particles as selective adsorbent for the removal of basic dye methylene blue. Because of their extremely high functional group density and unique strucutre, the as-designed particles show super adsorption capacity (1603 mg g−1 for methylene blue), ultra fast adsorption/desorption rates, facile separation and easy regeneration.

Importance of Micropore-Mesopore Interfaces in Carbon Dioxide Capture by Carbon-Based Materials.

Mesoporous carbonaceous materials (Starbons®) derived from low-value/waste bio-resources separate CO2 from CO2 /N2 mixtures. Compared to Norit activated charcoal (AC), Starbons® have much lower microporosities (8-32 % versus 73 %) yet adsorb up to 65 % more CO2 . The presence of interconnected micropores and mesopores is responsible for the enhanced CO2 adsorption. The Starbons® also showed three-four times higher selectivity for CO2 adsorption rather than N2 adsorption compared to AC.

Importance of Micropore–Mesopore Interfaces in Carbon Dioxide Capture by Carbon‐Based Materials

AbstractMesoporous carbonaceous materials (Starbons®) derived from low‐value/waste bio‐resources separate CO2 from CO2/N2 mixtures. Compared to Norit activated charcoal (AC), Starbons® have much lower microporosities (8–32 % versus 73 %) yet adsorb up to 65 % more CO2. The presence of interconnected micropores and mesopores is responsible for the enhanced CO2 adsorption. The Starbons® also showed three–four times higher selectivity for CO2 adsorption rather than N2 adsorption compared to AC.

Preparation of three-dimensional interconnected mesoporous anatase TiO2-SiO2 nanocomposites with high photocatalytic activities

In this article, we report the preparation of a three-dimensional (3D) interconnected mesoporous anatase TiO2-SiO2 nanocomposite. The nanocomposite was obtained by using an ordered two-dimensional (2D) hexagonal mesoporous anatase 70TiO2-30SiO2-950 nanocomposite (crystallized at 950 °C for 2 h) as a precursor, NaOH as an etchant of SiO2via a “creating mesopores in the pore walls” approach. Our strategy adopts mild conditions of creating pores such as diluted NaOH solution, appropriate temperature and solid/liquid ratio, etc. aiming at ensuring the integrities of mesopores architecture and anatase nanocrystals. XRD, TEM and N2 sorption techniques have been used to systematically investigate the physico-chemical properties of the nanocomposites. The results show that the intrawall mesopores are highly dense and uniform (average pore size 3.6 nm), and highly link the initial mesochannels in a 3D manner while retaining mesostructural integrity. There is no significant change to either crystallinity or size of the anatase nanocrystals before and after creating the intrawall mesopores. The photocatalytic degradation rates of rhodamine B (RhB, 0.303 min−1) and methylene blue (MB, 0.757 min−1) dyes on the resultant nanocomposite are very high, which are 5.1 and 5.3 times that of the precursor; even up to 16.5 and 24.1 times that of Degussa P25 photocatalyst, respectively. These results clearly demonstrate that the 3D interconnected mesopores structure plays an overwhelming role to the increments of activities. The 3D mesoporous anatase TiO2-SiO2 nanocomposite exhibits unexpected-high degradation activities to RhB and MB in the mesoporous metal oxide-based materials reported so far. Additionally, the nanocomposite is considerably stable and reusable. We believe that this method would pave the way for the preparation of other 3D highly interconnected mesoporous metal oxide-based materials with ultra-high performance.

The electrospun mesoporous Al2O3 and mesoporous Au–Al2O3 nanofiber catalyst

The one-dimensional mesoporous alumina nanofibers were prepared in larger scale by an improved electrospinning method and a subsequent calcination treatment. The existence of abundant interconnected mesopores on the obtained alumina nanofibers was observed and proved by the FE-SEM and TEM characterization. The formation of mesopores was attributed to the solvent evaporation induced surfactant assembly (SEISA) occurred during the process of electrospinning. Nitrogen adsorption–desorption analysis showed the mesoporous alumina nanofibers possessed large specific surface area up to 264 m2/g and the average pore size of 6.1 nm with a narrow distribution. After a treatment with HAuCl4·3H2O, it turned to a mesoporous Au/Al2O3 nanofiber material. This material was used as a heterogeneous catalyst in a model reaction to catalyze the oxidation of benzyl alcohol with hydrogen peroxide (H2O2). The catalyst test exhibited a high catalytic activity, and the turn over frequency value of this model reaction was calculated up to 879.

On the Mesoporogen-Free Synthesis of Single-Crystalline Hierarchically Structured ZSM-5 Zeolites in a Quasi-Solid-State System.

Hierarchically structured zeolites (HSZs) have gained much academic and industrial interest owing to their multiscale pore structures and consequent excellent performances in varied chemical processes. Although a number of synthetic strategies have been developed in recent years, the scalable production of HSZs single crystals with penetrating and three-dimensionally (3-D) interconnected mesopore systems but without using a mesoscale template is still a great challenge. Herein, based on a steam-assisted crystallization (SAC) method, we report a facile and scalable strategy for the synthesis of single-crystalline ZSM-5 HSZs by using only a small amount of micropore-structure-directing agents (i.e., tetrapropylammonium hydroxide). The synthesized materials exhibited high crystallinity, a large specific surface area of 468 m(2) g(-1) , and a pore volume of 0.43 cm(3) g(-1) without sacrificing the microporosity (≈0.11 cm(3) g(-1) ) in a product batch up to 11.7 g. Further, a kinetically controlled nucleation-growth mechanism is proposed for the successful synthesis of single-crystalline ZSM-5 HSZs with this novel process. As expected, compared with the conventional microporous ZSM-5 and amorphous mesoporous Al-MCM-41 counterparts, the synthesized HSZs exhibited significantly enhanced activity and stability and prolonged lifetime in model reactions, especially when bulky molecules were involved.

Beyond Creation of Mesoporosity: The Advantages of Polymer‐Based Dual‐Function Templates for Fabricating Hierarchical Zeolites

Direct synthesis of hierarchical zeolites currently relies on the use of surfactant‐based templates to produce mesoporosity by the random stacking of 2D zeolite sheets or the agglomeration of tiny zeolite grains. The benefits of using nonsurfactant polymers as dual‐function templates in the fabrication of hierarchical zeolites are demonstrated. First, the minimal intermolecular interactions of nonsurfactant polymers impose little interference on the crystallization of zeolites, favoring the formation of 3D continuous zeolite frameworks with a long‐range order. Second, the mutual interpenetration of the polymer and the zeolite networks renders disordered but highly interconnected mesopores in zeolite crystals. These two factors allow for the synthesis of single‐crystalline, mesoporous zeolites of varied compositions and framework types. A representative example, hierarchial aluminosilicate (meso‐ZSM‐5), has been carefully characterized. It has a unique branched fibrous structure, and far outperforms bulk aluminosilicate (ZSM‐5) as a catalyst in two model reactions: conversion of methanol to aromatics and catalytic cracking of canola oil. Third, extra functional groups in the polymer template can be utilized to incorporate desired functionalities into hierarchical zeolites. Last and most importantly, polymer‐based templates permit heterogeneous nucleation and growth of mesoporous zeolites on existing surfaces, forming a continuous zeolitic layer. In a proof‐of‐concept experiment, unprecedented core–shell‐structured hierarchical zeolites are synthesized by coating mesoporous zeolites on the surfaces of bulk zeolites.

Ionic Liquids as Electrolytes for Electrochemical Double-Layer Capacitors: Structures that Optimize Specific Energy.

Key parameters that influence the specific energy of electrochemical double-layer capacitors (EDLCs) are the double-layer capacitance and the operating potential of the cell. The operating potential of the cell is generally limited by the electrochemical window of the electrolyte solution, that is, the range of applied voltages within which the electrolyte or solvent is not reduced or oxidized. Ionic liquids are of interest as electrolytes for EDLCs because they offer relatively wide potential windows. Here, we provide a systematic study of the influence of the physical properties of ionic liquid electrolytes on the electrochemical stability and electrochemical performance (double-layer capacitance, specific energy) of EDLCs that employ a mesoporous carbon model electrode with uniform, highly interconnected mesopores (3DOm carbon). Several ionic liquids with structurally diverse anions (tetrafluoroborate, trifluoromethanesulfonate, trifluoromethanesulfonimide) and cations (imidazolium, ammonium, pyridinium, piperidinium, and pyrrolidinium) were investigated. We show that the cation size has a significant effect on the electrolyte viscosity and conductivity, as well as the capacitance of EDLCs. Imidazolium- and pyridinium-based ionic liquids provide the highest cell capacitance, and ammonium-based ionic liquids offer potential windows much larger than imidazolium and pyridinium ionic liquids. Increasing the chain length of the alkyl substituents in 1-alkyl-3-methylimidazolium trifluoromethanesulfonimide does not widen the potential window of the ionic liquid. We identified the ionic liquids that maximize the specific energies of EDLCs through the combined effects of their potential windows and the double-layer capacitance. The highest specific energies are obtained with ionic liquid electrolytes that possess moderate electrochemical stability, small ionic volumes, low viscosity, and hence high conductivity, the best performing ionic liquid tested being 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide.

Interconnected hierarchical HUSY zeolite-loaded Ni nano-particles probed for hydrodeoxygenation of fatty acids, fatty esters, and palm oil

Hierarchical H-style ultra-stable Y (HUSY) zeolites with abundant interconnected mesopores have been prepared using a sequential post-synthesis strategy that includes steaming dealumination and mixed-alkali desilication.

Preparation of Pt/C cathode catalyst supported on chestnut-like mesoporous carbon for fuel cell applications

Fuel cells have received worldwide attention as a next-generation renewable energy technology. However, catalyst cost and durability are the main issue hampering the commercialization of fuel cells. Many studies have focused on the physicochemical properties of the carbon support to improve the catalyst’s properties. Mesoporous carbons are suitable candidates because of their appropriate structural characteristics, including high surface area, large pore size, and regularly interconnected mesopores that permit efficient diffusion of the reactants and by-products. In this study, supports made from chestnut-like carbon consisting of platelet carbon nanofibers were fabricated by selective catalytic gasification of activated carbon. Pt/C catalysts were synthesized from these support structures using the impregnation method. Catalyst performance and characteristics were investigated by N2 adsorption/desorption isotherms, X-ray diffractions, and the rotating disk electrode technique for the oxygen reduction reaction.

Catalyst Design by NH4OH Treatment of USY Zeolite

Hierarchical zeolites are a class of superior catalysts which couples the intrinsic zeolitic properties to enhanced accessibility and intracrystalline mass transport to and from the active sites. The design of hierarchical USY (Ultra‐Stable Y) catalysts is achieved using a sustainable postsynthetic room temperature treatment with mildly alkaline NH4OH (0.02 m) solutions. Starting from a commercial dealuminated USY zeolite (Si/Al = 47), a hierarchical material is obtained by selective and tuneable creation of interconnected and accessible small mesopores (2–6 nm). In addition, the treatment immediately yields the NH4+ form without the need for additional ion exchange. After NH4OH modification, the crystal morphology is retained, whereas the microporosity and relative crystallinity are decreased. The gradual formation of dense amorphous phases throughout the crystal without significant framework atom leaching rationalizes the very high material yields (>90%). The superior catalytic performance of the developed hierarchical zeolites is demonstrated in the acid‐catalyzed isomerization of α‐pinene and the metal‐catalyzed conjugation of safflower oil. Significant improvements in activity and selectivity are attained, as well as a lowered susceptibility to deactivation. The catalytic performance is intimately related to the introduced mesopores, hence enhanced mass transport capacity, and the retained intrinsic zeolitic properties.

Expanding Beyond the Micropore: Active-Site Engineering in Hierarchical Architectures for Beckmann Rearrangement

The ability to engineer discrete solid-acid centers within hierarchically porous architectures that contain micropores with interconnected mesopores offers the potential to overcome the spatial restraints and diffusional limitations imposed by conventional microporous zeotype catalysts, which often lead to decreased catalyst lifetimes and restricted substrate scope. By employing a one-step soft-templating approach, coupled with detailed physicochemical and spectroscopic characterization, isolated, solid-acid sites can be suitably tailored and discretely modulated within the micropores and mesopores. The design strategy facilitates a synergistic enhancement in catalytic activity, selectivity, substrate versatility, and longevity, compared to analogous microporous zeotypes that have been extensively employed in the chemical industry, as solid-acid catalysts, for the production of e-caprolactam (precursor for Nylon-6).

Conductometric sensor for ammonia and ethanol using gold nanoparticle-doped mesoporous TiO2

We describe uniform and high-temperature-stable mesoporous TiO2 beads functionalized with gold nanoparticles (AuNPs-TiO2) for use in conductometric sensing of gases and organic vapors. The size of the interconnected main mesopores of the TiO2 beads ranges from 8 to 15 nm, and the AuNPs have diameters between 8 and 10 nm. The mesoporous TiO2 beads are formed during calcination while the structure-directing template agent is removed. Monodispersed AuNPs are formed by reduction in-situ and are placed inside the mesoporous TiO2 framework. This prevents aggregation of the AuNPs even at 500 °C. The materials were characterized by UV–vis spectroscopy, scanning and transmission electron microscopy, nitrogen adsorption-desorption, and X-ray diffraction. Comb-type gold electrodes were then fabricated on an alumina substrate and are shown to display excellent properties in terms of sensing ammonia, ethanol, methanol or acetone. The sensitivity (defined as the ratio of resistivities under vapor and air) of a typical AuNPs(0.5 %)-TiO2 gas sensor for ethanol reached up to 5.65 at above 600 ppm at 75 °C. Response time and recovery times (t90 ≤ 20 s) are faster than (or comparable to) other metal-doped TiO2 sensors, and working temperatures are much lower. An interesting observation was made in that the changes in the conductivity of the sensor change with temperature. The sensor prepared with AuNPs(0.5 %)-TiO2 is of the p-type (in its response to ammonia gas) at 45 °C, but becomes n-type at 20 °C. Obviously, rather slight changes in temperature lead to a complete change in the direction of the conductometric signal change. This may provide a new aspect in terms of selective and highly sensitive detection of ammonia at ambient and slightly elevated temperatures.

Preparation and characterisation of MCM‐41 materials with intra‐wall cross‐mesopores

A series of novel mesoporous MCM-41 (Mobil Composition of Matter No. 41) materials has been synthesised using pre-organo-functionalised fumed silica as the silica source. Subsequent X-ray diffraction, nitrogen/argon adsorption and transmission electron microscopy analyses indicated that the additional mesopores formed in silica walls seem to cross the inherent hexagonally arranged channels, affording interconnected structural mesopores. Compared with the conventional MCM-41 material featuring single cylindrical pores, the newly prepared materials have a larger surface area (1450 m2/g), and their adsorption capacity for n-heptane has been enhanced in the low-pressure region, which presumably would be highly beneficial to the abatement of low-concentration volatile organic compounds.

Direct Synthesis of Phosphorus‐Doped Mesoporous Carbon Materials for Efficient Electrocatalytic Oxygen Reduction

AbstractChemical doping has been recognized as a promising route to achieve novel physicochemical functions of porous carbons as metal‐free catalysts in renewable energy‐related technologies, such as electrochemical oxygen reduction reaction (ORR). However, it remains challenging to exploit an effective method for the synthesis of metal‐free carbonaceous electrocatalysts. Herein, we report the direct synthesis of phosphorus‐doped mesoporous carbonaceous electrocatalysts for the first time through soft‐templating method, in which organophosphonic acid serves as the phosphorus source. The resulting mesoporous carbon material possesses high doping level, large surface area, and an interconnected mesopore system, ensuring the sufficient exposure and availability of catalytic sites to realize considerable catalytic activity for ORR in alkaline media. More importantly, much better tolerance for methanol oxidation, higher durability, and comparable Tafel slopes as compared with the commercial Pt/carbon (Pt/C) catalyst are valuable for developing alternative fuel cells and metal–air batteries.

Porous MgO material with ultrahigh surface area as the matrix for phase change composite

Mesoporous magnesium oxide (MgO) material was synthesized using an integration of the evaporation-induced surfactant assembly and magnesium nitrate pyrolysis. The as-prepared MgO material is well crystalline, and possesses three-dimensional interconnected mesopores and a surface area as high as 596m2/g. Using the porous MgO as a matrix and polyethylene glycol (PEG-1000) as the functional phase for heat energy storage, a shape-stabilized phase change composite of PEG/MgO was fabricated by an easy impregnation method. In the composite, mesoporous MgO material provides structural strength and prevents the leakage of the molten PEG during the phase change process. The compositions and microstructures of the PEG/MgO composite were determined by Fourier transformation infrared spectroscope (FT-IR), X-ray diffractometer (XRD), scanning electronic microscope (SEM) and thermogravimetric analyzer (TGA), respectively. The phase change properties of the PEG/MgO composite were determined by differential scanning calorimeter (DSC). The high heat-energy storage capability and good thermal stability of the composite enable it extensive applications in the future.

Effect of mesocelluar carbon foam electrode material on performance of vanadium redox flow battery

Languid reaction rate of VO2+/VO2+ redox couple is a problem to solve for improving performance of vanadium redox flow battery (VRFB). To facilitate the slow reaction materials including large pore sized mesocellular carbon foam (MSU-F-C and Pt/MSU-F-C) are used as new catalyst. Their catalytic activity and reaction reversibility are estimated and compared with other catalysts, while cycle tests of charge–discharge and polarization curve tests are implemented to evaluate energy efficiency (EE) and maximum power density (MPD). Their crystal structure, specific surface area and catalyst morphology are measured by XRD, BET and TEM. The new catalysts indicate high peak current ratio, small peak potential difference and high electron transfer rate constant, proving that their catalytic activity and reaction reversibility are superior. Regarding the charge–discharge and polarization curve tests, the VRFB single cells including new catalysts show high EE as well as low overpotential and internal resistance and high MPD. Such excellent results are due to mostly unique characteristics of MSU-F-C having large interconnected mesopores, high surface area and large contents of hydroxyl groups that serve as active sites for VO2+/VO2+ redox reaction and platinums (Pts) supporting the MSU-F-C. Indeed, employment of the catalysts including MSU-F-C leads to enhancement in performance of VRFB by facilitating the slow VO2+/VO2+ redox reaction.

Microporous–mesoporous ZSM-12 zeolites: Synthesis by using a soft template and textural, acid and catalytic properties

The influence of the amount of amphiphilic organosilane TPOAC {[3-(trimethoxy-silyl)propyl] octadecyldimethylammonium chloride} added in the synthesis and of the crystallization time in the textural, acid and catalytic properties of microporous–mesoporous ZSM-12 (MMZ12) zeolites was investigated. XRD/Rietveld Refinement, N2 sorption measurements, SEM, EDX, and NH3-TPD were used to sample characterization and the performance as acid catalysts verified using the transformation of cyclohexane as a model reaction. WAXRD data showed that the usage of short synthesis times and increasing amounts of TPOAC in the synthesis led to ZSM-12 zeolites with poor crystallinity due to the organosilane steric constraints to MTW nuclei formation and crystal growth. On the other hand, SAXRD and N2 sorption data evidenced that TPOAC firstly generates a pseudo-ordered mesoporous phase, which is transformed into well-crystalline hierarchical MMZ12 zeolites tailoring the synthesis conditions. Were obtained samples with a relatively broad mesopore size distribution having mean diameters close to 4.0nm and slightly higher external surface areas and lower amounts of strong acid sites than the only microporous ZSM-12 one. The MMZ12 zeolites showed similar cyclohexane conversion and lower deactivation rate due to coke formation than a conventional ZSM-12 that were attributed to a balance of two opposite effects, a lower strong acidity and the presence of HRTEM evidenced interconnected micropores and mesopores that reduce the 3D internal diffusion limitations. The yield and selectivity on the conventional ZSM-12 were coherent with the transformation of cyclohexane on 12-ring H-zeolites, nevertheless on the microporous–mesoporous ones the yield to C6 saturated hydrocarbons increased with the increase of the mesoporous volume, then disfavoring the yield to saturated and unsaturated light hydrocarbons.