Studies on functionalized mesoporous materials—Part I: characterization of silylized mesoporous material of type MCM-41

The synthesis of organic–inorganic composite materials was performed by the surface modification of mesoporous material type MCM-41 by chlorodimethylphenylsilane and dichloromethylphenylsilane. Applying IR spectroscopy, low temperature nitrogen adsorption/desorption (isotherms BET), thermogravimetric measurements and technique of competitive adsorption of toluene and water it was shown that the degree of silylation, hydrophobicity, surface and volume properties (pore size distribution, pore volume) strongly depends on the nature of silylation agent and the ratio of calculated amount of silanol groups to the modifier. Two types of condensation reaction take place: (1) the reaction of the modifier with surface silanol groups, and (2) an inter-molecular condensation of the modifier, resulting in additional pore blocking. Only 24–36 % of the surface silanol groups react with modifier agent. The materials are stable up to temperatures of about 170 °C that is higher than the corresponding polymeric resins. The TG/DTA data allowed concluding that the degree of grafting depends on the ratio silylation agent to SiOH groups. As shown by Fourier transform diffuse reflectance mode spectroscopy only free silanol groups react with modifier.     

Properties of Desilicated ZSM-5, ZSM-12, MCM-22 and ZSM-12/MCM-41 Derivatives in Isomerization of α-Pinene

Limited information is available on the isomerization of α-pinene proceeding on zeolites and related desilicated materials. We wish therefore to report on the title reaction proceeding over ZSM-5, ZSM-12 and MCM-22 type zeolites, parent and modified by the sodium hydroxide treatment. The NaOH solutions of various concentrations (0.05–1 M) were used as a desilicating agent. Such treatments with basic solutions were applied: (i) under atmospheric pressure, and (ii) under hydrothermal conditions. It was shown that ZSM-12 was more resistant towards the basic solutions treatment, and its structure was retained over a whole range of NaOH concentrations studied. Nitrogen sorption revealed strong influence of the desilication process on the pore structure of modified materials—the mesopores system was formed in the zeolite crystals. Finally, catalytic studies were carried out using ZSM-5, ZSM-12, MCM-22, their desilicated derivatives and a ZSM-12/MCM-41 composite material. Catalytic properties of the samples studied were affected to a large extent by the NaOH treatment.     

Bifunctional mesoporous Cu–Al–MCM-41 materials for the simultaneous catalytic abatement of NOx and VOCs

This study explored the possibility of using waste organic solvent as the source of volatile organic compound (VOC) and it served as a reducing agent of selective catalytic reduction (SCR) deNO_x process, in which the VOC itself can be catalytically oxidized on the mesoporous Cu and/or Al substituted MCM-41 catalysts. The synthesized Cu–Al–MCM-41 catalysts were extensively characterized by powder low-angle X-ray diffraction (XRD), N₂ adsorption–desorption measurements, transmission electron microscopy (TEM), UV–Visible diffuse reflectance spectroscopy (UV–Vis DRS), ²⁷Al magic angle spinning-nuclear magnetic resonance spectroscopy (MAS-NMR), electron paramagnetic resonance spectroscopy (EPR) and inductively coupled plasma–mass spectrometer (ICP–MS) analysis. The XRD, TEM and N₂ adsorption–desorption studies clearly demonstrated the presence of a well ordered long range hexagonal array with uniform mesostructures. The Cu–Al–MCM-41 materials showed a better long-term-stability than that of copper ion-exchanged H–ZSM-5 (Cu–ZSM-5) zeolite. The Cu–Al–MCM-41 material was found to be an efficient catalyst than that of Cu–MCM-41 without aluminum for the simultaneous catalytic abatement of NO_x and VOCs, which was attributed to the presence of well dispersed and isolated Cu²⁺ ions on the Cu–Al–MCM-41 catalyst as observed by UV–Vis DRS and EPR spectroscopic studies. And the presence of aluminum (Al³⁺ ions) within the framework of Cu–Al–MCM-41 stabilized the isolated Cu²⁺ ions thus it led to higher and stabilized activity in terms of NO_x reduction.     

Development of electrochemical cell with layered composite of the Gd-doped ceria/electronic conductor system for generation of H2–CO fuel through oxidation–reduction of CH4–CO2 mixed gases

This paper shows the recent results on the development of layered composite promoting two types of electrochemical reactions (oxidation and reduction) in one cell. This cell consisted of porous Ni–Gd-doped (GDC) ceria cathode/thin porous GDC electrolyte (50 μm)/porous SrRuO₃–GDC anode. The external electric current was flowed in this cell at the electric field strength of 1.25 and 6.25 V/cm. The mixed gases of CH₄ (30–70%) and CO₂ (70–30%) were fed at the rate of 50 ml/min to the cell heated at 400–800 °C under the electric field. In the cathode, CO₂ was reduced to CO (CO₂ + 2e^? → CO + O^2?) and the formed CO and O^2? ions were transported to the anode through the pores and surface and interior of grains of GDC film. On the other hand, CH₄ was oxidized in the anode to form CO and H₂ through the reaction with diffusing O^2? ions (CH₄ + O^2? → CO + 2H₂ + 2e^?). As a result, H₂–CO mixed fuel was produced from the CH₄–CO₂ mixed gases (CH₄ + CO₂ → 2H₂ + 2CO). This electrochemical reaction proceeded completely at 800 °C and no blockage of gases was measured for long time (>10 h). Only H₂–CO fuel was generated in the wide gas compositions of starting CH₄–CO₂ gases.     

The selective catalytic reduction activity of Cu/MCM-41 catalysts prepared by using the Cu2+–MCM-41 mesoporous materials with copper ions in the framework as precursors

The Cu²⁺–MCM-41 mesoporous materials with different loadings of copper species in the framework have been prepared by hydrothermal method and characterized by using various physico-chemical methods combined with the selective catalytic reduction of NO by NH₃. It has been shown that the particle size of metallic copper formed after hydrogen reduction is much smaller than that in the supported catalysts prepared by impregnation method, and that the SCR activity of catalyst increases obviously with the increase of Cu content to 10 wt.% because of its higher dispersion of copper metal in the mesoporous catalyst even at higher Cu loading.     

Design of spark plasma sintering parameters and preparation of Al2O3/TiB2/TiC micro–nano composite ceramic tool material

A microstructure evolution model for the ceramic materials was constructed, and the spark plasma sintering parameters were optimized using the model to shorten the designing period and reduce the consumption of the material. Based on the optimized sintering parameters, the ceramic tool material with a composition of Al₂O₃, TiB₂, and TiC proved to be a success. It verified that the materials prepared under the optimized sintering parameters exhibited excellent mechanical properties. The results showed when sintered at 1600°C, under the pressure of 40 MPa and with the holding period of 7 min, the materials with 70% Al₂O₃, 20% TiB₂, and 10% nano-TiC possess the relatively best performance, with the hardness, fracture toughness, and flexure strength being 20.3 GPa, 10.5 MPa/m², and 839.5 MPa, respectively.     

Convenient solvent-free synthesis and characteristics of acid–base bifunctionalized MCM-41 mesoporous silicas

A series of acid?Cbase bifunctionalized mesoporous silicas have been successfully synthesized by means of a convenient solvent-free approach. Through grinding the precursors, aluminium and magnesium nitrates, with the as-prepared MCM-41, and then the generation of acid?Cbase sites and removal of host template were simultaneously completed in the subsequent calcination procedure. The resultant modified mesoporous silicas MgO?CAl₂O₃?CMCM-41 were characterized with X-ray diffraction, high-resolution transmission electron microscopes, N₂ adsorption, FT-IR spectra, ²⁹Si and ²⁷Al MAS NMR, NH₃? and CO₂? temperature programmed desorption. The results indicate that the products exhibit excellent acid?Cbase properties with well mesoporous structure, and the guests were well dispersed in the channel of MCM-41, which make it exhibit high activity for the synthesis of EMC.     

Sulfur infiltrated mesoporous graphene–silica composite as a polysulfide retaining cathode material for lithium–sulfur batteries

The lithium–sulfur (Li–S) system is an attractive candidate to replace the current state-of-the-art lithium-ion battery due to the promising theoretical charge capacity of 1675 mA h/g and energy density of 2500 Wh/kg; however, the dissolution of intermediate polysulfides into the organic liquid electrolyte during cycling hinders its practical realization. We report the synthesis of mesoporous graphene–silica composite (m-GS) as a supporting material of sulfur for Li–S batteries. The ordered porous silica structure was synthesized parallel to functionalized graphene sheets (FGSs) through the ternary cooperative assembly of the graphene, silica, and block copolymer precursors. The well-defined, unique mesoporous structure integrates the electronic conductivity of graphene and the dual functions of silica as a structure building block and in situ polysulfide ab-/ad-sorbing agent to give a Li–S battery that has both good retention ability of polysulfides and good rate capability.     

Effect of the Synthesis Method on Co-catalysts Based on MCM-41 for the Fischer–Tropsch Reaction

In this work, cobalt catalysts based on ordered mesoporous materials of the MCM-41 type were synthesized and characterized. The synthesis of the catalysts was performed by using different methods: impregnation; incorporation of the metal in the synthesis gel and ionic exchange of the metal by the template. Different characterization techniques were used (N₂ adsorption–desorption, XRD, TPR, SEM and XPS) to study the textural and structural properties of the samples and the metal-support interaction corresponding to each method of synthesis. These samples were tested in the CO Hydrogenation (Fischer–Tropsch Synthesis) by measuring the CO conversion and the selectivity to CO₂ and some groups of hydrocarbons chains. The results show that structural and textural properties as well as the metal-support interactions are affected by the synthesis method. According to this study, catalytic performance is related to the properties of the samples, observing that the metal support interaction highly affects the activity and selectivity of the catalysts.     

Temperature effect on the photo-epoxidation of propylene over V–Ti/MCM-41 photocatalyst

The effect of reaction temperature on the gas-phase photocatalytic epoxidation of propylene was systematically studied over V–Ti/MCM-41 photocatalyst at different temperatures (298–393 K). Temperature significantly influences the product distribution of photo-epoxidation. Raising temperature is favorable towards the formation of propionaldehyde (PA) due to inhibition of PA transformation to propionic acid (C₂H₅COOH), the intermediate product of acetaldehyde (AA). Results indicated that the reaction temperature has a dual-action to the reaction rate: (1) improving the desorption of reaction products, which provides more active sites for reaction and (2) reducing the adsorption of propylene on the photocatalyst, which declines the reaction efficiency.     

Cobalt‐containing smectite‐like mesoporous material as a new type of catalyst for hydrodesulfurization of thiophene

Cobalt‐containing mesoporous smectite‐like material (SM(Co)) was prepared by a hydrothermal method and used as a catalyst for hydrodesulfurization (HDS) of thiophene. It is active by itself and produces mainly butenes and a small amount of n-butane. When platinum is added to this material, the HDS activity is enhanced by 50%, while the product distribution does not change so much. The platinum‐loaded sample should have two types of active sites, one originally present in the smectite‐like material and the other with platinum, the latter being different in nature from a sample of platinum supported on silica gel. Thus, the SM(Co) and Pt/SM(Co) samples are new types of HDS catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effective diffusion constant and adsorption constant of synthesized alumina,zirconia, and alumina–zirconia composite material

In this study, Al₂O₃, ZrO₂, and Al₂O₃–ZrO₂ composite materials were prepared with the sol–gel technique. X-ray diffraction analysis, differential scanning calorimetry–thermogravimetry, scanning electron microscopy–energy-dispersive X-ray spectrometry, nitrogen adsorption isotherm measurements, and helium pycnometry were used to characterize the resultant materials. Effective diffusion coefficients of helium and hydrogen and the adsorption equilibrium constant of hydrogen in the resultant materials were determined using single-pellet moment technique. The effective diffusivities of helium and hydrogen in both ZrO₂ and Al₂O₃–ZrO₂ composite pellets were found to be smaller than the value found for Al₂O_3, due to the lower tortuosity factor values of the Al₂O₃ pellet. It was found that hydrogen was weakly adsorbed on all resultant materials.     

Separation of COCO2N2 gas mixture for high-purity CO by pressure swing adsorption

A pressure swing adsorption (PSA) process for separating CO from a COCO₂N₂ mixture is proposed. The adsorbent used in this process is active carbon supported copper, which has been developed by this laboratory. By cycling the pressure of a bed of this adsorbent between ambient pressure and 20–30 Torr at room temperature, high purity CO can be obtained from the COCO₂N₂ gas mixture with a high recovery. The CO product purity depends crucially on the step of CO cocurrent purge after adsorption in the cycle and the regeneration of sorbent.     

Selective adsorption of CO2/N2 promoted by polar ligand functional groups of metal–organic frameworks

Journal of Porous Materials - The structure modification of metal–organic frameworks (MOFs) is a promising technique to enhance its selective adsorption of carbon dioxide at room...     

Preparation and electrochemical performance of SiCN–CNTs composite anode material for lithium ion batteries

The composite of silicon carbonitride (SiCN) and carbon nanotubes (CNTs) was synthesized by sintering the mixture of polysilylethylenediamine-derived amorphous SiCN and multi-walled CNTs at a temperature of 1,000 °C for 1 h in argon. The as-prepared SiCN–CNTs material, which was used as anode active substance in a lithium ion battery, showed excellent electrochemical performance. Charge–discharge tests showed the SiCN–CNTs anode provided a high initial specific discharge capacity of 1176.6 mA h g⁻¹ and a steady specific discharge capacity of 450–400 mA h g⁻¹ after 30 charge–discharge cycles at 0.2 mA cm⁻². Both of the abovementioned values are higher than that of pure polymer-derived SiCN, CNTs, and commercial graphite at the same charge–discharge condition. It was deduced that the CNTs in the composite not only improved the electronic conductivity and offered channels and sites for the immigrating and intercalating of Li⁺ but also stabilized the structure of the composite.