ClO<Stack><Subscript>4</Subscript><Superscript>−</Superscript></Stack>/Al-MCM-41 nanoparticles as a solid acid catalyst for the synthesis of 2-amino-3-cyanopyridines

A one-pot four-component reaction of various types of aldehydes, acetophenone, malononitrile, and ammonium acetate was studied in the presence of perchlorated Al-MCM-41 (ClO ₄ ^? /Al-MCM-41) nanoparticles for the synthesis of 2-amino-3-cyanopyridines. Mesoporous Al-MCM-41 molecular sieves with the Si/Al molar ratios of 30, 40, and 50 were synthesized by the sol–gel method and ClO ₄ ^? /Al-MCM-41 with different calcination temperatures were prepared and characterized by SEM, TEM, XRD, FT-IR, potentiometric titration and, N₂ adsorption-desorption techniques. The characterization results show that ClO ₄ ^? /Al-MCM-41 with calcination temperature of 300 °C has the best catalytic activity for the synthesis of 2-amino-3-cyanopyridines. The catalyst is reusable many times with moderate loss in its activity.     

固载于 Al-MCM-41 纳米孔道中的钒离子催化氧化烷基芳基硫化物

 VOSO₄ immobilized within nanoreactors of Al-MCM-41 (VO²⁺/Al-MCM-41) was synthesized and characterized by X-ray diffraction, Fourier transform infrared spectroscopy, nitrogen adsorption-desorption, and chemical analysis techniques. The prepared VO²⁺/Al-MCM-41 successfully catalyzes the oxidation of aryl alkyl sulfides and up to 99% conversion and 90% selectivity for the corresponding sulfoxides were obtained with H₂O₂ as oxidant in acetonitrile at room temperature in 30 min.     

Effect of the catalyst MCM-41 on the kinetic of the thermal decomposition of poly(ethylene terephthalate)

The aim of this work is to determine the activation energy for the thermal decomposition of poly(ethylene terephthalate)—PET, in the presence of a MCM-41 mesoporous catalyst. This material was synthesized by the hydrothermal method, using cetyltrimethylammonium as template. The PET sample has been submitted to thermal degradation alone and in presence of MCM-41 catalyst at a concentration of 25% in mass (MCM-41/PET). The degradation process was evaluated by thermogravimetry, at temperature range from 350 to 500 °C, under nitrogen atmosphere, with heating rates of 5, 10 and 25 °C min^?1. From TG, the activation energy, determined using the Flynn–Wall kinetic method, decreased from 231 kJ mol^?1, for the pure polymer (PET), to 195 kJ mol^?1, in the presence of the material (MCM-41/PET), showing the catalyst efficiency for the polymer decomposition process.     

Catalytic Disproportionation of Methyltrichlorosilane by AL-MCM-41 to Prepare Dichlorodimethylsilane

Abstract

Al-MCM-41 samples with various Si/Al ratios were prepared and then used to disproportionate methyltrichlorosilane (MTS) to produce dichlorodimethylsilane (DMCS). The catalysts were characterized by FT-IR, X-ray powder diffraction (XRD), ²⁷Al magic angle spinning nuclear magnetic resonance (²⁷Al MAS NMR), inductively coupled plasma atomic emission spectroscopy (ICP-AES), and N₂ absorption–desorption. It reveals that all samples show the hexagonal structure of MCM-41 and exhibit large BET surface areas (over 842 m²·g^?1). FT-IR spectra of pyridine adsorption demonstrates that Al-MCM-41 samples have Lewis (L) and Brønsted (B) acidic sites, and the B acidic sites are stable in the temperature ranging from 423 to 623 K. The effects of aluminum content and temperature on the disproportionation reaction were also investigated. The results show that the Al-MCM-41 with the Si/Al ratio of 15:1 exhibits an excellent activity with 100% conversion of MTS and 47% selectivity of DMCS at 623 K under atmospheric pressure.     

Th(IV) adsorption on mesoporous molecular sieves: effects of contact time,solid content,pH, ionic strength,foreign ions and temperature

The mesoporous molecular sieves (Al-MCM-41) are synthesized with montmorillonite as silica–alumina source by hydrothermal method. The application of Al-MCM-41 for the adsorption of Th(IV) from aqueous solution is studied by batch technique. The effects of contact time, solid content, pH, ionic strength, foreign ions, and temperature are determined, and the results indicate that the adsorption of Th(IV) to Al-MCM-41 is strongly dependent on pH values but independent of ionic strength. The adsorption isotherms are simulated by D–R and Freundlich models well. The thermodynamic parameters (ΔH ⁰, ΔS ⁰, ΔG ⁰) are calculated from the temperature dependent adsorption isotherms at 293, 313 and 333 K, respectively, and the results suggest that the adsorption of Th(IV) on Al-MCM-41 is a spontaneous and endothermic process. Al-MCM-41 is a suitable material for the preconcentration of Th(IV) from large volumes of aqueous solutions.     

环境水样中痕量铅的中孔分子筛Al-MCM-41分离富集-火焰原子吸收法测定

建立了中孔分子筛Al-MCM-41分离富集-火焰原子吸收光谱法测定水样中痕量铅的新方法。采用扫描电镜(SEM)、红外光谱(IR)等检测方法对自制的中孔分子筛Al-MCM-41吸附材料进行了表征,优化了中孔分子筛Al-MCM-41对试液中痕量铅的吸附和解吸条件。在pH5.5时,室温振荡20 min,中孔分子筛Al-MCM-41能定量、快速吸附水中的痕量Pb2+,其静态饱和吸附容量为2.5 mg/g。吸附在中孔分子筛Al-MCM-41上的Pb2+可用0.2 mol/L EDTA完全洗脱。其他金属离子共存不影响铅的测定。洗脱铅后的吸附材料经再生可循环使用10次以上。Pb2+的线性范围为0.5~30 mg/L,富集后方法检出限(3σ)为0.05μg/L,对5 mg/L的Pb2+溶液平行测定11次,相对标准偏差为1.2%,加标回收率为98%~104%。该方法用于环境水样中铅的测定,结果满意。     

Synthesis and characterization of mesoporous molecular sieves

In the synthesis of mesoporous molecular sieves of the type MCM-41, different cationactive surfactants and sources of silicon were used. Moreover, Al-MCM-41 samples with different content of aluminium were synthesized. MCM-41 and Al-MCM-41 were synthesized at elevated temperature in stainless-steel autoclaves. Prepared mesoporous molecular sieves were characterized by powder X-ray diffraction (XRD), physical adsorption of nitrogen at the temperature of −197°C, sorption capacity of benzene, and by infrared spectroscopy (FTIR). Acidity was measured for Al-MCM-41 by temperature programmed desorption of ammonia (TPDA) and by FTIR of adsorbed pyridine. Acid catalytic activity of Al-MCM-41 was tested by isomerization of o-xylene. Influence of the synthesis reproducibility, surfactant used, source of silicon, synthesis time, source of aluminium, and Si to Al mole ratio on the properties of mesoporous molecular sieves were evaluated.     

Influence of cross profile of PE fibers on thermal properties of materials

Molecular sieves MCM-41 were synthesized from rice husk ash (RHA) as alternative sources of silica, called RHA MCM-41. The material was synthesized by a hydrothermal method from a gel with the molar composition 1.00 CTMABr:4.00 SiO₂:1.00 Na₂O:200.00 H₂O at 100 °C for 120 h with pH correction. The cetyltrimethylammonium bromide (CTMABr) was used as a structure template. The material was characterized by X-ray powder diffraction, FTIR, TG/DTG, and surface area determination by the BET method. The kinetics models proposed by Ozawa, Flynn–Wall, and Vyazovkin were used to determine the apparent activation energy for CTMA⁺ species decomposition from the pores of MCM-41 material. The results were compared with those obtained from the MCM-41 synthesized with silica gel. The synthesized material had specific surface area, size, and pore volume as specified by mesoporous materials developed from conventional sources of silica.     

The effect of Pt nanoparticles distribution on the removal of cyanide by TiO2 coated Al-MCM-41 in blue light exposure

With an aim to enhance the photocatalytic activity, Pt loaded TiO₂–Al-MCM-41 catalysts with high surface area were synthesized by a multistep route. The waste of the rice processing, rice husk (RH), was used as the precursor for the extraction of silica. The diffuse reflectance and photoluminescence spectroscopy revealed the extension of the absorption edge in the visible region and exciton trapping nature of the dispersed platinum. The structural analysis was carried out by XRD, whereas X-ray photoelectron spectroscopy identified the chemical states of the components of the synthesized powders. The BET surface area measurements revealed the reduction in the surface area and pore volume with the increasing platinum loading. TEM micrographs showed the uniform distribution of TiO₂ and Pt nanoparticles at the surface of Al-MCM-41. The photocatalytic efficiency of the synthesized powders as photocatalysts was obtained for the removal of 100 ppm CN⁻ from aqueous solution in fluorescent blue light exposure. Compared to unsupported TiO₂, the Pt-loaded catalysts exhibited substantially high activity for the removal of CN⁻. A plausible mechanism for the removal of cyanide ions was proposed. The catalysts showed excellent stability and reproducibility in the successive use.     

Simultaneous Removal of H<Subscript>2</Subscript>S and Dust in the Tail Gas by DC Corona Plasma

The removal of hydrogen sulfide and dust simultaneously by the DC corona discharge plasma with a wire-cylinder reactor was studied at atmospheric pressure and room temperature. The outlet gases were analyzed by Fourier Transform Infrared. Chemical compositions of the dust collected from ground electrode were analyzed by X-ray fluorescence. The results showed that the DC corona discharge is effective in removing H₂S and dust simultaneously. The best H₂S conversion was gained with the 2 cm discharge gap. The lower inlet H₂S concentration, the higher conversion efficiency was gained at any specific input energy (SIE), while the energy yield was on the contrary. The removal efficiency of H₂S decreased gradually as oxygen concentration increased, which means that the H₂S decomposition mainly depends on direct electron collisions or short-living species, such as^·O, ^·OH radicals in the non-thermal plasma. At the initial stage, the conversion efficiency of H₂S increased with the increasing of relative humidity, but later decreased while the relative humidity keep increasing with the same SIE. Existing of dust can not only reduce the energy consumption of H₂S conversion and improve the removal efficiency, but also inhibit the yield of SO₂ for it can further react with some compounds in the dust. With the discharge gap of 2 cm, inlet H₂S concentration of 2400 ppm, O₂ Of 0.5 %, relative humidity of 41 %, dust content of 4000 ± 5 % mg/m³ and SIE of 600 J/L, the H₂S conversion reached 98.8 %, and the dust removal efficiency was close to 100 %.     

Thermal decomposition kinetic evaluation and its thermal hazards prediction of AIBN

AIBN (2,2′-azobis (isobutyronitrile)), widely used for blowing agent and initiator, is a typical self-reactive material, being capable of undergoing runaway reaction due to its self-heating during storage or transportation. In this study, the thermal decomposition process of AIBN was studied by differential scanning calorimetry at different heating rates. The kinetic parameters including the activation energy and pre-exponential factor at different stages were calculated, and the laws of parameter variation were analyzed using the software, named as Advanced Kinetics and Technology Solutions, which can also predict the thermal stability of decomposition process at actual situations, such as ton and kg scale. The results show that heating rate can influence evidently the thermal behavior of AIBN, which can decompose in liquid phase or in liquid–solid co-existing phase, or, even decomposes in solid phase; according to Friedman method, the value of the calculated activation energy is 122 kJ mol^?1; according to Ozawa method, the value decreases gradually with the reaction process, and the smallest one is 124 kJ mol^?1. By mg-scale prediction under isothermal condition, it is known that AIBN decomposes at 30 °C (room temperature), very slowly; by ton-scale prediction under adiabatic condition, the safety diagram of AIBN is acquired, which shows how the time to the maximum rate changes with the initial temperature under ideal adiabatic condition (Φ = 1), for example, for TMR_ad = 24 h, the corresponding mean temperature (i.e., TD₂₄) is 71.23 °C, and for the initial temperature 71.23 °C, the lower and upper limits of the confidence intervals (95 % probability) are 18.5 and 31 h; by kg-scale prediction, it is obtained that the self-accelerating decomposition temperature of 50 kg AIBN with standard package is 63 °C, which is close to that of ARC.     

Model-free kinetics analysis of decomposition of polypropylene over Al-MCM-41

Both thermal and catalytic decomposition of PP sample is studied to understand the effect of catalyst (Al-MCM-41) on the decomposition behaviour. Mesoporous catalyst (Al-MCM-41) is synthesized by sol–gel methods and characterized by X-ray diffraction (XRD) analysis and nitrogen adsorption study. The optimum catalyst composition is found to be around 18.5 wt%, where the reduction in maximum decomposition temperature is around 103 °C. The nonlinear Vyazovkin model-free technique is applied to evaluate the quantitative information on variation of E with for PP sample under both catalytic and noncatalytic nonisothermal conditions.

The constant pattern behaviour of the TG curves and the similar trend on variation of E with for both catalytic and noncatalytic decomposition of PP indicates similar mechanism involved during decomposition. The only effect of catalyst is observed in the form of reduction of the temperature and the activation energy. The literature reported data on such variation are compared with the results of the present study. Results show that Al-MCM-41 is superior to the ZSM-5 catalyst in terms of catalyst loading due to the existence of larger external macropore and mesopore surface in it.     

Effect of the AL-MCM-41 catalyst on the catalytic pyrolysis of atmospheric petroleum residue (ATR)

Thermogravimetry (TG) was used in this study to evaluate thermal and catalytic pyrolysis of Atmospheric Petroleum Residue (ATR) which can be found in the state of Rio Grande do Norte/Brazil, after a process of atmospheric distillation of petroleum. The utilized sample in the process of catalytic pyrolysis was Al-MCM-41, a mesoporous material. The procedures for obtaining the thermogravimetric curves were performed in a thermobalance with heating rates of 5, 10, and 20 °C min⁻¹. From TG, the activation energy was determined using the Flynn–Wall kinetic method, which decreased from 161 kJ mol⁻¹, for the pure ATR, to 71 kJ mol⁻¹, in the presence of the Al-MCM-41, showing the efficiency of the catalyst in the pyrolysis of Atmospheric Petroleum Residue.     

Thermogravimetric analysis of walnut shell as pyrolysis feedstock

Thermal degradation behavior and kinetics of a biomass waste material, namely walnut shell, were investigated by using a thermogravimetric analyzer. The desired final temperature of 800 °C was achieved at three different heating rates (2, 10, and 15 °C min^?1) under nitrogen flow (50 mL min^?1). The TG and DTG curves exhibited three distinct zones that can mainly be attributed to removal of water, decomposition of hemicellulose + cellulose, and decomposition of lignin, respectively. The kinetic parameters (activation energy, pre-exponential factor, and reaction order) of active pyrolysis zone were determined by applying Arrhenius, Coats?CRedfern, and Horowitz?CMetzger methods to TG results. The values of activation energies were found to be between 45.6 and 78.4 kJ mol^?1. There was a great agreement between the results of Arrhenius and Coats?CRedfern methods while Horowitz?CMetzger method yielded relatively higher results. The existence of kinetic compensation effect was evident.     

Liquid-phase synthesis of isopulegol from citronellal using mesoporous molecular sieves mcm-41 and zeolites

Isopulegol (IPG) was synthesized from citronellal (CTN) at atmospheric pressure and 40~60°C in a batch reactor by using mesoporous molecular sieves MCM-41 as well as zeolites HZSM-5 and Hβ. The catalysts were characterized by the methods of XRD, N₂ adsorption, ²⁷Al and ²⁹Si MAS-NMR and TPD of ammonia. Under our reaction conditions, Al-MCM-41 was found to be the best catalyst; it exhibited much higher activity, despite slightly lower IPG selectivity. The catalytic results depend on a variety of factors, viz. the acidity, the pore size and the pore channel of catalysts. The reaction paths were proposed and the kinetic parameters for competitive first order reactions of CTN were estimated. This revised version was published online in June 2006 with corrections to the Cover Date.     

中孔分子筛Al-MCM-41制备及催化合成二芳基乙烷

以硅酸钠为硅源、硫酸铝为铝源、CTAB为模板剂,采用水热法合成了负载型固体酸Al-MCM-41中孔分子筛催化剂,并通过X射线衍射（XRD）、热重差热分析（TG-DTA）、扫描电镜（SEM）和红外（IR）方法对其进行了表征,同时研究了该催化剂在二芳基乙烷合成反应中的催化性能。考察了各种反应因素的影响,确定其最佳合成条件为：原料苯乙烯与二甲苯质量之比为1∶7.5,催化剂用量为1 %(总投料质量百分比),反应时间为3 h,反应温度为140 ℃,产率可达87.1 %,比传统催化剂浓硫酸提高了17 %。研究结果表明,该催化剂是替代液体酸合成二芳基乙烷的理想固体酸催化剂。     

Reaction of benzaldehyde with various aliphatic glycols in the presence of hydrophobic Al-MCM-41: A convenient synthesis of cyclic acetals

The reaction of benzaldehyde with aliphatic glycols was performed over Al-MCM-41 with various Si/Al ratios. The effects of various parameters like temperature, mole ratio, reaction time and catalyst amount on the formation of acetals were optimized. The mesoporous Al-MCM-41 (Si/Al ratio 36, 57, 81 and 108) were synthesized by hydrothermal method. The synthesized catalysts were characterized by X-ray diffraction (XRD), nitrogen adsorption–desorption isotherm (BET), thermo gravimetric-differential thermal analysis (TGA-DTA) and TEM techniques. The acidity of the catalysts was measured by pyridine adsorption followed by FT-IR analysis. TEM analysis showed that the honeycomb-like regular arrangement of hexagonal pores on the molecular sieves. The highly hydrophobic Al-MCM-41 (108) showed higher activity than the other Si/Al ratios. The activity of the catalysts showed the following order Al-MCM-41 (108) > Al-MCM-41 (81) > Al-MCM-41 (57) > Al-MCM-41 (36). The hydrophobicity and nucleophilicity of the glycols highly influences the conversion of benzaldehyde, it followed the order; hexylene glycol (HG) > propylene glycol (PG) > ethylene glycol (EG). The results showed that mole ratio of 1:3 (aldehyde:glycol) gave higher yield than the other mole ratios.     

Growth,structural, crystallisation,thermal decomposition and dielectric behaviour of melaminium bis(hydrogen oxalate) single crystal

Single crystals of melaminium bis (hydrogen oxalate) (MOX) single crystals have been grown from aqueous solution by slow solvent evaporation method at room temperature. X-ray powder diffraction analysis confirms that MOX crystallises in monoclinic system with space group C2/c. The calculated lattice parameters are a = 20.075 ± 0.123 Å b = 8.477 ± 0.045 Å, c = 6.983 ± 0.015 Å, α = 90°, β = 102.6 ± 0.33°, γ = 90° and V = 1,159.73 (Å)³. Thermogravimetric analysis at three different heating rates 10, 15 and 20 °C min^?1 has been done to study the thermal decomposition behaviour of the crystal. Non-isothermal studies on MOX reveal that the decomposition occurs in two stages. Kinetic parameters [effective activation energy (E _a), pre-exponential factor (ln A)] of each stage were calculated by model-free method: Kissinger, Kim–Park and Flynn–Wall method and the results are discussed. A significant variation in effective activation energy (E _a) with conversion progress (α) indicates that the process is kinetically complex. The linear relationship between the ln A and E _a was established (compensation effect). DTA analyses were conducted at different heating rates and the activation energy was determined graphically from Kissinger and Ozawa equation. The average effective activation energy is calculated as 276 kJ mol^?1 for the crystallization peak. The Avrami exponent for the crystallization peak temperature determined by Augis and Bennett method is found to be 1.95. This result indicates that the surface crystallization dominates overall crystallization. Dielectric study has also been done, and it is found that both dielectric constant and dielectric loss decreases with increase in frequency and is almost a constant at high frequency region.     

介孔分子筛Al-MCM-41制备及催化合成二芳基乙烷

以硅酸钠为硅源、硫酸铝为铝源、CTAB为模板剂,采用水热法合成了骨架负载型固体酸Al-MCM-41介孔分子筛催化剂,并通过X射线衍射(XRD)、扫描电子显微镜(SEM)和红外(IR)方法对其进行了表征,同时研究了该催化剂在二芳基乙烷合成反应中的催化性能. 考察了各种反应因素的影响,确定其最佳合成条件为:原料m(苯乙烯)∶m(二甲苯)=1∶7.5,催化剂用量为1%(总投料质量分数),反应时间为3 h,反应温度为140 ℃,产率可达87.1%,比传统催化剂浓硫酸提高了17%. 研究结果表明,该催化剂是替代液体酸合成二芳基乙烷的理想固体酸催化剂.     

Non-isothermal crystallization kinetics of a Si–Ca–P–Mg bioactive glass

In this work, the crystallization process of a SiO₂–3CaO·P₂O₅–MgO glass was studied by non-isothermal measurements using differential thermal analysis carried out at various heating rates. X-ray diffraction at room and high temperature was used to identify and follow the evolution of crystalline phases with temperature. The activation energy associated with glass transition, (E _g), the activation energy for the crystallization of the primary crystalline phase (E _c), and the Avrami exponent (n) were determined under non-isothermal conditions using different equations, namely from Kissinger, Matusita & Sakka, and Osawa. A complex crystallization process was observed with associated activation energies reflecting the change of behavior during in situ crystal precipitation. It was found that the crystallization process was affected by the fraction of crystallization, (x), giving rise to decreasing activation energy values, E _c(x), with the increase of x. Values ranging from about 580 kJ mol^?1 for the lower crystallized volume fraction to about 480 kJ mol^?1 for volume fractions higher than 80 % were found. The Avrami exponents, calculated for the crystallization process at a constant heating rate of 10 °C min^?1, increased with the crystallized fraction, from 1.6 to 2, indicating that the number of nucleant sites is temperature dependent and that crystals grow as near needle-like structures.