Synthesis of spherical mesoporous silica nanoparticles with nanometer-size controllable pores and outer diameters

Spherical mesoporous silica particles with tunable pore size and tunable outer particle diameter in the nanometer range were successfully prepared in a water/oil phase using organic templates method. This method involves the simultaneous hydrolytic condensation of tetraorthosilicate to form silica and polymerization of styrene into polystyrene. An amino acid catalyst, octane hydrophobic-supporting reaction component, and cetyltrimethylammonium bromide surfactant were used in the preparation process. The final step in the method involved removal of the organic components by calcinations, yielding the mesoporous silica particles. Interestingly, unlike common mesoporous materials, the particle with controllable pore size (4–15 nm) and particle diameter (20–80 nm) were produced using the method described herein. The ability to control pore size was drastically altered by the styrene concentration. The outer diameter was mostly controlled by varying the concentration of the hydrophobic molecules. Relatively large organic molecules (i.e. Rhodamine B) were well-absorbed in the prepared sample. Furthermore, the prepared mesoporous silica particles may be used efficiently in various applications, including electronic devices, sensors, pharmaceuticals, and environmentally sensitive pursuits, due to its excellent adsorption properties.     

大颗粒超高纯度硅溶胶的制备及其表征(英文)

采用新工艺路线制备四乙氧基硅烷（tetraethoxysilane,TEOS）,以TEOS为原料制备超纯度大颗粒硅溶胶。TEOS是烷氧基硅烷法制备甲硅烷的副产物,经过精馏提纯以后,加入盐酸或氨水催化剂,采用溶胶-凝胶法制备硅溶胶。结果表明：TEOS和硅溶胶金属杂质离子总含量都低于0.3mg/L。用盐酸催化TEOS水解制备溶胶,胶粒直径达到129nm;用氨水催化,胶粒直径达272nm。当物质的量比n（C2H5OH）/n（TEOS）=6,n（H2O）/n（TEOS）=5,搅拌速度为250 r/min,制备的硅溶胶胶粒均匀度最好。加水不搅拌,胶粒很容易发生团聚,但是,当搅拌速率高于500 r/min时,胶粒出现团聚现象。     

Esterification reaction of oleic acid with a fusel oil fraction for production of lubricating oil

In this study, the esterification of oleic acid with a fraction of fusel oil was investigated. The variables that affect ester yield, such as temperature, molar ratio of oleic acid to alcohol, and amount of catalyst, were determined. Powdered silica gel was chosen to remove water instead of granular silica gel, magnesium sulfate, or benzene. The behavior of amyl alcohols and the fusel oil fraction was compared. The esterification reaction was carried out under the reaction conditions selected as optimal, and the ester conversion of the reaction was 97.3%. The product mixture compressed products, excess reactants, catalyst, and desiccant. Oleate ester and oleic acid (2.7%) were obtained using the refinement steps of filtration, evaportation, washing with distilled water, and drying over sodium sulfate.     

Graft-polymerization of phosphine functionalized monomers onto silica particles

Summary Triphenylphosphine (PPh₃), a well-known reagent and catalyst, was successfully grafted onto silica particles in a functionalized polymer form using 4-(diphenylphosphinyl)styrene as a monomer. 4-(Diisopropylphosphinyl)styrene and 4-(ditertbutylphosphinyl)styrene were also grafted onto silica in the form of a functionalized polymer and oligomer, respectively. Two methods were used: A) Copolymerization of phosphine-functionalized monomers with a vinyl compound previously attached to silica; and B) Polymerization of phosphine-functionalized monomers using a radical initiator previously attached to silica. The resulting materials were characterized by FTIR, DTA-TGA, specific surface area (S_BET) and XPS. The best results in grafting percent and molecular weight of the grafts were obtained by method B. Received: 7 February 2002 /Revised: 10 July 2002/ Accepted: 10 July 2002     

Oxidation of ethyl alcohol in trickle bed reactors: Analysis of the conversion rate

The interpretation of results of a chemical reaction carried out in a trickle bed reactor is not immediate when the key reactants are volatile; in fact some authors state that the overall conversion rate increases at very low liquid flow rates, i.e. when the catalyst is unevenly wetted. In these conditions, the reactants may penetrate inside the catalyst pellets directly through the “dry” zones; therefore the mass transfer resistance is diminished and the conversion rate can be increased. To investigate this phenomenon tests on the catalytic oxidation of ethyl alcohol dissolved in water were performed at different operating conditions in a trickle bed reactor. An interpretation of the results was tried by using two different models based on partially wetted particles. This approach considers both the cases in which “dry” zones are active or not for mass transfer and mass transfer rates are affected or not by the chemical reaction.     

Increased Metal Utilization in Carbon‐Supported Pt Catalysts by Adsorption of Preformed Pt Nanoparticles on Colloidal Silica

Pt/C electrocatalysts, aimed at maximizing the electrochemical surface area (ECSA) and consequently the specific mass activity of fuel cell reactions, are obtained by firstly depositing Pt nanoparticles on colloidal silica (Pt‐silica), followed by the adsorption of the latter onto a carbon support. This method of catalyst preparation increases Pt metal utilization and generates accessible void space in the interpenetrating particle network of carbon and silica for the facile transport of reactants and products. Both electrochemical hydrogen adsorption/desorption and CO oxidation measurements show an increase in the ECSA using this approach. Methanol electrooxidation is used as a test reaction to evaluate the catalytic activity. It is found that the silica modified catalyst is three times as active as a catalyst prepared without silica, under otherwise identical conditions.     

New macromolecular silane coupling agents synthesized by living anionic polymerization; grafting of these polymers onto inorganic particles and metals

New macromolecular silane coupling agents, which are end-triethoxysilylated poly(styrene) and poly(tert-butylmethacrylate), were investigated as possible inorganic particle and metal surface treatment agents. These polymers containing poly(styrene) and poly(tert-butylmethacrylate) as the main chain, were prepared by living anionic polymerization. Grafting of the polymers onto inorganic particles and metals was performed via the hydrolysis of the triethoxysilyl group using either acidic or basic catalyst. n-Butylphosphate was used as the catalyst for grafting onto inorganic substances having an acidic surface such as silica. However, in the case of grafting onto inorganic substances having a basic surface, tetrabutylammoniumhydroxide was employed as the catalyst. Contrary to expectations, grafting onto titania was successful even in the absence of a catalyst. Particles grafted with these polymers showed excellent dispersibility in organic medium, in which the polymers are soluble. This phenomenon is in contrast to that for particles treated with polymers possessing triethoxysilyl groups at random positions of the chain or those treated with trimethylsilyl groups. Surface tension measurements of metal substrates coated with the grafted polymers, were found to be identical to the values obtained for the bulk polymers.     

Characterization by Mössbauer spectroscopy of trimetallic Pd–Sn–Au/Al2O3 and Pd–Sn–Au/SiO2 catalysts for denitration of drinking water

The reduction of nitrate using a catalytic process is one of the most interesting ways to solve the problem of drinking water pollution by this compound. The key parameter of this technique is the selectivity toward nitrogen formation. Palladium/tin-based bimetallic catalysts are well suited for this purpose, but the selectivity of these catalysts is not high enough for a direct application of this process. In the present study, alumina- and silica-supported catalysts were prepared by successive deposition of tin and gold onto palladium particles by using controlled surface reaction. The characterization of trimetallic Pd–Sn–Au catalyst evidenced that trimetallic catalysts supported on silica present a palladium/tin/gold phase. The catalytic test showed that this type of catalyst is very active and selective in nitrate and nitrite reduction. Moreover, the addition of gold improves the stability and the selectivity toward nitrogen formation of the catalyst compared to the parent Pd–Sn catalyst.     

Interpenetrating polymer networks derived from silylated soybean oil and polydimethylsiloxane

A series of interpenetrating polymer networks (IPNs) was prepared using various concentrations of silylated soybean oil and polydimethylsiloxane (PDMS) that were cross linked with inorganic silicates. This series of IPNs was prepared from emulsions of silylated soybean oil and PDMS together with colloidal silica and dioctyltin dilaurate catalyst at pH 10. Under these conditions, water soluble silicates reacted with silanols in the oil phase and formed intraparticle siloxane cross links. Upon casting films and evaporation of the water, additional interparticle cross linking were obtained between the coagulating particles to produce entangled networks of soybean oil and PDMS that were further reinforced by fine silica particles. The morphology revealed intimate mixing of the two immiscible components. The mechanical properties depended on the ratio of the soft, flexible PDMS phase and the rigid, brittle cross linked silylated soybean oil phase. These IPNs can be used as high release liners, low friction materials, or as a general protective coating. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2479–2486, 2013     

Kinetics of esterification of palmitic acid with isopropanol using p‐toluene sulfonic acid and zinc ethanoate supported over silica gel as catalysts

Kinetic data on the esterification of palmitic acid with isopropanol were obtained using homogeneous (para‐toluene sulfonic acid, p‐TSA) and heterogeneous (zinc ethanoate coated on silica gel, ZnA/SG) catalysts in a batch reactor. The ZnA/SG catalyst was prepared using a sol–gel technique. The esterification reaction was studied at different reaction temperatures (373–443 K), initial reactants molar ratio (1–5), catalyst loading (1–5 gcat dm^?3) and water concentration in feed (0–15 vol%). A power law rate equation was used for homogeneous kinetics analysis. The Langmuir Hinshelwood Hougen Watson (LHHW) model was used for heterogeneous kinetics. The kinetic parameters of both models were obtained using Polymath software. The reaction parameters were used to obtain simulated values of conversion for both catalytic systems. The simulated values were compared with the experimental values and were in good agreement. Copyright © 2004 Society of Chemical Industry     

Preparation of Fischer–Tropsch cobalt catalysts supported on carbon nanofibers and silica using homogeneous deposition-precipitation

Homogeneous deposition-precipitation on either a silica or carbon nanofiber (CNF) support of cobalt from basic solution using ammonia evaporation was studied and compared with conventional deposition from an acidic solution using urea hydrolysis. In the low-pH experiment, the interaction between precipitate and silica was too high; cobalt hydrosilicates were formed requiring a reduction temperature of 600 °C, resulting in low cobalt dispersion. Lower interaction in experiments performed in a basic environment yielded a well-dispersed Co₃O₄ phase on silica, and after reduction at only 500 °C, a catalyst with 13-nm cobalt particles was obtained. On CNF from an acidic solution, cobalt hydroxy carbonate precipitated and displayed a low interaction with the support resulting after reduction at 350 °C in a catalyst with 25-nm particles. From basic solution we obtained high dispersion of cobalt on the CNF, probably related to the greater ion adsorption. After drying, Co₃O₄ crystallites were obtained that, after reduction at 350 °C, resulted in a catalyst with 8-nm Co particles. Samples prepared in the high-pH experiment had 2–4 times higher cobalt-specific activity in the Fischer–Tropsch reaction than their low-pH counterparts. CNF support materials combined with the high-pH deposition-precipitation technique hold considerable potential for cobalt-based Fischer–Tropsch catalysis.     

Performances of a catalytic foam trap for soot abatement

A catalytic trap for soot particles was prepared by deposition of Cu–V–K–Cl catalyst on a ceramic foam. Catalytic trap performances were evaluated by treating the exhaust of a gas oil burner under different operating conditions. The results obtained showed that ceramic foam is a particularly suitable support for this application since it yields low gas pressure drop, good soot collection efficiency (“deep bed” filtration mechanism), high thermal shock resistance and good contact throughout the filter between soot particles and catalyst surface. In addition, the catalytic foam trap is able to spontaneously regenerate at operating conditions comparable to those typical of diesel engine exhaust and after more than 70 test hours it retains its activity towards soot oxidation.     

Control of hydroxyl group content in silica particle synthesized by the sol-precipitation process

This study investigated the control of hydroxyl groups, one of key factors determining the surface properties of silica particles synthesized by the sol-precipitation of tetraethyl orthosilicate (TEOS). Thus, a thermal gravity analysis (TGA) was used to facilitate quantitative measurements of the hydroxyl groups on the silica particles, while BET and FT-IR were used to analyze the specific surface area and functional silane groups on the silica particles, respectively. In the sol-precipitation process, silanes that include various hydroxyl groups are formed as intermediates based on the hydrolysis and condensation of TEOS. Thus, NH₃, as a basic catalyst initiating the nucleophilic substitution of TEOS, was found to accelerate the hydrolysis and increase the hydroxyl group content on the silica particles. Plus, the hydroxyl group content was also increased when increasing the concentrations of TEOS and water as the hydrolysis reactants. However, the hydroxyl group content was reduced when increasing the temperature, due to the promotion of condensation. Based on the weight loss of the particles according to the thermal analysis, the hydroxyl group content on the silica particles varied from 5.6–42.7 OH/nm² under the above reaction conditions.     

Preparation of hairy particles by grafting PEG onto the poly(styrene‐co‐maleic anhydride) surface and PEG effect on SiO2 nanoparticles adsorption

Hairy particles were prepared by immobilization of poly(ethylene glycol) (PEG) on the surface of poly(styrene‐co‐maleic anhydride) (poly(S‐co‐MA)) spheres. It was found that the carbonyl groups on the poly(S‐co‐MA) surface can be conveniently esterified with the hydroxyl groups of PEG. Chemical and morphological changes were analyzed by FT‐IR, TEM, and water contact angle. Results revealed that, with the immobilization of PEG, the morphology of poly(S‐co‐MA) turned from a smooth surface to a hairy‐like structure and the hydrophilicity of the polymer particles improved. In addition, berry‐like polymer/silica particles can be obtained by using the hairy particles as template. The PEG hairy chains show steric repulsion during the deposition of silica nanoparticles by in situ sol‐gel process. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

新型多酸-有机亚胺-分子筛杂化材料的氧化催化性能

利用3-氨基丙基三甲氧基硅修饰的SBA-15、苯甲醛以及过渡金属单取代Keggin型杂多酸盐(SiNiW11)合成了一系列有序介孔二氧化硅杂化材料(SiNiW -Schiff-SBA-15).通过对杂化材料进行表征,证明SiNi11的Keggin单元以及希夫碱配体在负载之后结构保持完整,并研究了杂化材料的形貌和表面物理...     

Beyond shape selective catalysis with zeolites: Hydrophobic void spaces in zeolites enable catalysis in liquid water

Zeolites confine active sites within void spaces of molecular dimension. The size and shape of these voids can be tuned by changing framework topology, which can influence catalytic reactivity and selectivity via coupled reaction‐transport phenomena that exploit differences in transport properties among reactants and/or products that differ in size and shape. The polarity and solvating properties of intrazeolite void environments can be tuned by changing chemical composition and structure, ranging from hydrophobic defect‐free pure‐silica surfaces to silica surfaces containing hydrophilic defect sites and/or heteroatoms. Here, we discuss how the polarity of zeolite voids influences catalytic reactivity and selectivity via the partitioning of reactant, product, and solvent molecules between intrazeolitic locations and external fluid phases. These findings provide a conceptual basis for developing selective catalytic processes in aqueous media using hydrophobic zeolites that are able to adsorb organic reactants while excluding liquid water from internal void spaces. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3349–3358, 2013     

Study on application of membrane reactor in direct synthesis DMC from CO2 and CH3OH over Cu–KF/MgSiO catalyst

Membrane catalytic reactor (MCR) combing catalytic reaction with membrane separating process has exhibited a promising pathway to improve reaction conversion and selectivity for its selective permeating products online or controlling the addition of key reactants. In this work, three types of supported membranes (i.e. silica inorganic membrane, polyimide-silica and polyimide-titania hybrid membranes) and copper catalyst supported on MgO–SiO₂ composite substrate modified by KF were prepared, were used as MCRs materials and catalyst, respectively, for the direct synthesis of dimethyl carbonate (DMC) from carbon dioxide and methanol. The influences of operating conditions on the conversion of methanol and the selectivity to DMC were discussed. The results show that hybrid membranes have excellent thermal and hydrophilic properties and that water vapor diffusing through them obeyed surface flow mechanism. The reaction behaviors of MCR are higher than those of CCR with the conversion of methanol improved remarkably and the selectivity to DMC increase a few under proper reaction conditions. The catalytic reaction performances are controlled mainly by the characters of catalyst, and the incorporation of MCRs has not changed the reaction mechanism, which played the primary roles as the concentration distributors in the catalytic reaction system.     

Nonisothermal cure kinetics of diglycidylether of bisphenol‐A/amine system reinforced with nanosilica particles

Epoxy‐silica nanocomposites were obtained from directly blending diglycidylether of bisphenol‐A (DGEBA)‐based epoxy and nanoscale silica (NS) and then curing with 4,4′‐diaminodiphenylamine (DDA). The effect of amount of nanosilica (NS) particles as catalyst on the mechanism and kinetic parameters of cure reaction of DGEBA/DDA system was studied. The kinetics parameters were obtained from nonisothermal differential scanning calorimeter (DSC) data using the Kissinger and Ozawa equations. The exothermic peak was shifted toward lower temperatures in DGEBA/DDA/NS system with increasing the amount of nanoslica particles. However, the existence of NS particles with hydroxyl groups in the structure in the mixture of DGEBA/DDA catalyzes the cure reaction and increases the rate constant. The activation energy of cure reaction of DGEBA/DDA system obtained from two methods were in good agreement, and showed a decrease when NS particles were present in the mixture. The mechanism of reaction of DGEBA with DDA was carried out by isothermal curing in the oven at 130°C and measuring the disappearance peak of epoxide group at 916 cm^?1 using FTIR. The diffusive behavior of two systems was investigated during water sorption at 25°C and the experimental results fitted well to Fick's law. Diffusion coefficient of cured sample from DGEBA/DDA/10% NS blend decreased in comparison with the sample without NS particles. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3855–3863, 2007     

Preparation and nonisothermal cure kinetics of DGEBA‐nanosilica particles composites

Nanocomposites from nanoscale silica particles (NS), diglycidylether of bisphenol‐A based epoxy (DGEBA), and 4,4′‐diaminobiphenyl benzidine (DAPB) as curing agent were obtained from direct blending of these materials. This homogenous mixture was cured in the oven at a particular temperature for a certain time or scanned from room temperature up to 300°C in differential scanning calorimeter (DSC). Mechanism and kinetic of the cure reaction of nanocomposite and thermal stability of the cured sample were studied with FTIR, DSC, and thermogravimetric analysis, respectively. The effect of amount of nanosilica (NS) particles as catalyst on the cure reaction of DGEBA/DAPB system was studied by the Kissinger and Ozawa equations. The existence of NS particles with hydroxyl groups in the structure catalyzes the cure reaction of DGEBA/DAPB system, increased the rate constant, and shifted the exothermic peak toward lower temperatures with increasing amount of NS particles. The activation energies of cure reaction of pure DGEBA/DAPB system obtained from two methods were in good agreement and decreased when NS particles were present in the mixture. The isothermal cure reaction at 145°C in an oven was followed by measuring the disappearance peak of epoxide group at 916 cm⁻¹ using FTIR. The diffusive behavior of cured samples was investigated during water sorption at 25°C and the experimental results fitted well according to Fick's law. Diffusion coefficient of cured sample containing 10% NS decreased in comparison to the sample without NS particles. POLYM. COMPOS., 2008. © 2007 Society of Plastics Engineers     

硅胶负载四氯化锡催化合成丁醛乙二醇缩醛

以硅胶负载四氯化锡为催化剂,丁醛和乙二醇为原料,合成丁醛乙二醇缩醛。研究了原料摩尔比、催化剂用量、反应时间等因素对产品收率的影响。结果表明,硅胶负载四氯化锡有较高的催化活性,当丁醛与乙二醇的摩尔比为1∶1．5,环己烷为带水剂,催化剂用量占反应原料总质量的1．0％,反应时间为1．5h时,丁醛乙二醇缩醛的收率可达87．3％。