Synthesis characterization and catalytic evaluation of Ni/ZrO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> aerogels catalysts

The Ni/ZrO₂/SiO₂ aerogels catalysts were synthesized via three different routes: (i) impregnation ZrO₂–SiO₂ composite aerogels with a aqueous solution of Ni(NO₃)₂, (ii) impregnation SiO₂ aerogels with a mixed aqueous solution of Ni(NO₃)₂ and ZrO(NO₃)₂ · 2H₂O, (iii) one-pot sol–gel procedure from precursors Ni(NO₃)₂/ZrO(NO₃)₂ · 2H₂O/Si(OC₂H₅)₄. These catalysts were characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), ammonia temperature-programmed desorption (NH₃-TPD), N₂ adsorption–desorption isotherms and Fourier transform infrared (FT-IR). The Liquid-phase hydrogenation of maleic anhydride (MA) was performed over these catalysts. The results revealed that the different preparation routes result in a difference between the obtained samples, concerning the crystal structure and composition, surface acidity, mixed level of each component, texture, and catalytic selectivity.     

Formation and Crystallization Behavior of Gels in the Na2O-SiO2-TiO2-ZrO2 System

SiO₂-TiO₂-ZrO₂ and 5Na₂O·95(SiO₂ + TiO₂ + ZrO₂) gels were synthesized and role of Na₂O in gel formation and crystallization behavior of gels were studied. From Si(OC₂H₅)₄, Ti(iso-OC₃H₇)₄, Zr(n-OC₃H₇)₄ and NaOCH₃ solutions in EtOH without H₂O, transparent and opaque gels were obtained. Opaque bulk gels, rich in TiO₂ or ZrO₂ composition in Na₂O containing SiO₂-TiO₂-ZrO₂ system, contain agglomerated spherical particles of diameter small <10 m, in contrast with opaque gels having large particles <30 m in alkali-free SiO₂-TiO₂-ZrO₂ system. Crystallization temperature (Tc) was measured by DTA on dried gels. Compared with the alkali-free SiO₂-TiO₂-ZrO₂ gels, 5 mol% Na₂O containing gels gave lower Tc in SiO₂ rich compositions and higher in TiO₂ rich or ZrO₂ rich compositions.     

超临界流体干燥法制备纳米TiO2-SnO2-SiO2复合光催化剂及其光催化性能研究

半导体多相光催化法作为一种污染治理新技术越来越受到人们的重视,在所使用的半导体光催化剂中,TiO2以无毒,催化活性高,价廉,无污染等特点,成为最具有前途的绿色环保型催化剂之一[1],但其自身具有局限性,如禁带宽度大,需在近紫外光下才能激发产生电子空穴对,对太阳光的利用率仅     

α-Fe2O3/SiO2纳米颗粒混合体系表面的酸碱性质及其对重金属离子的吸附行为

以Fe(NO₃)₃·9H₂O和正硅酸乙酯(TEOS)为原料, 通过溶胶-凝胶法和辅助模板法分别制备了纳米α-Fe₂O₃和SiO₂, 并对所合成样品进行了粉末X射线衍射(XRD)和BET表征. 使用自动电位滴定仪测定了α-Fe₂O₃/SiO₂纳米颗粒混合体系的表面酸碱性质. 研究了在不同pH下α-Fe₂O₃/SiO₂混合体系对Cu²⁺、Pb²⁺、Zn²⁺离子的吸附行为. 基于上述实验数据, 用WinSGW软件计算了α-Fe₂O₃/SiO₂混合体系表面酸碱配位常数, 并得出结论: α-Fe₂O₃/SiO₂混合体系表面反应为单一脱质子反应≡XOH ⇔ ≡XO^-+ H⁺(lg K = -8.19±0.15), 明显区别于同时具有加质子和脱质子反应的α-Fe₂O₃/SiO₂/γ-Al₂O₃, α-Fe₂O₃/γ-Al₂O₃和SiO₂/γ-Al₂O₃等纳米颗粒混合体系. 在此基础上拟合得到α-Fe₂O₃/SiO₂混合体系吸附重金属离子Cu²⁺、Pb²⁺、Zn²⁺的表面络合反应平衡常数分别为:
≡XOH + M²⁺ ⇔ ≡XOM⁺+ H⁺ [lg K = -3.1, -3.6, -3.8 (M = Cu, Pb, Zn)].
≡XOH＋M²⁺＋H₂O ⇔≡XOMOH＋2H⁺[lg K = -8.8, -8.0, -10.5 (M = Cu, Pb, Zn)]     

Untersuchungen im System SrO?SiO2?H2O

Investigation on the System SrO? SiO₂? H₂O On addition sodium silicate solutions to solutions of Sr(OH)₂, at room temperature strontium hydrogensilicates are precipitated which are always amorphous and contain silicate anions of various condensation degrees. At about 100°C at first also amorphous products are formed containing lower- and higher-molecular silicate anions. On standing of these precipitates at about 80°C under the mother liquor, however, cristallization occurs under complete degradation of the higher-molecular anions to monomeric resp. dimeric silicate anions. In dependence on the Na₂O: SiO₂ ratio of the sodium silicate solutions and on the Sr(OH)₂ concentrations the following crystalline compounds are formed: 1.25 SrO · 1 SiO₂ · 2 H₂O, 3 SrO · 2 SiO₂ · 3 H₂O and 3 SrO · 2 SiO₂ · 4 H₂O, with monomeric silicate anions; 2 SrO · 2 SiO₂ · 1.5 H₂O; 2 SrO · 2 SiO₂ · 2 H₂O, and 2 SrO · 2 SiO₂ · 3 H₂O, with dimeric anions.     

Cs取代对Ni-H3PW12O40/SiO2催化剂结构性质和催化性能的影响

采用两步浸渍法和载体上的原位反应制备了一系列Cs部分取代的Ni-Cs_xH_3-xPW₁₂O₄₀/SiO₂催化剂,并用N₂吸附比表面积测定(BET)、电感耦合等离子体发射光谱(ICP)、X射线衍射(XRD)、拉曼光谱(Raman)、原位X射线衍射(in situ XRD)、NH₃程序升温脱附(NH₃-TPD)、H₂程序升温还原(H₂-TPR)、H₂程序升温脱附(H₂-TPD)、吡啶吸附傅里叶变换红外(FTIR)光谱等分析测试技术对催化剂进行了表征. 以正癸烷为模型化合物,对催化剂的加氢裂化性能进行了评价. 结果表明,8%Ni-50%Cs_1.5H_1.5PW/SiO₂催化剂具有最高的C₅₊收率,明显优于8%Ni-50%H₃PW/SiO₂催化剂和工业催化剂. 随着Cs 在Cs_xH_3-xPW中比例的增加,正癸烷的转化率逐渐降低,而C₅₊选择性则逐渐提高. 当催化剂具有合适的孔径时,选择性的提高是由于催化剂酸性的减弱,而转化率的降低则是由于催化剂加氢能力的减弱.     

Ab initio calculations of oxygen nuclear quadrupole coupling constants and oxygen and silicon NMR shielding constants in molecules containing SiO bonds

Ab initio coupled Hartree—Fock perturbation theory (CHFPT) calculations employing large gaussian basis sets have been used to evaluate the electric field gradient at O, q^o, and the NMR shieldings at O and Si, σ^o and σ^Si, in the molecules SiO, SiO₂, Si₂O₂, H₂SiO, SiO⁻⁴₄, Si(OH)₄ and (H₃Si)₂O. Species containing Si bonded to three or fewer atoms have small NMR shieldings at both O and Si while those with four-coordinate Si have systematically larger O and Si shieldings. A significant positive correlation is observed between calculated O and Si NMR shieldings. Reduction of the SiO distance in SiO⁴⁻₄ and H₃SiOSiH₃ gives a significant reduction in the magnitude of q^o and a small increase in σ. Anisotropies in σ^Si are large for two- and three-coordinate Si (200–900 ppm) but for (H₃Si)₂O the σ^Si anisotropy is only ≈60 ppm. Anisotropies in σ^o are generally larger than those in σ^Si, with values larger than 200 ppm for both SiO⁻⁴₄ and (H₃Si)₂O. Values of q^o for SiO⁴⁻₄ and (H₃Si)₂O are in qualitative agreement with experimentally determined values for nesosilicates and SiO₂ polymorphs, respectively, but all the q^o values appear to be exaggerated at the Hartree—Fock level. Also, q^o values are not greatly different for the exotic species SiO, Si₂O₂, etc. compared to the typical silicate models SiO⁴⁻₄ and (H₃Si)₂O. Calculated isotropic chemical shifts yield good values for the Si chemical shift differences of SiF₄, SiO⁴⁻₄ and (H₃Si)₂O and for the O chemical shift difference of SiO⁴⁻₄ and H₂O. For SiO⁴⁻₄ the paramagnetic contribution to the Si shift, σ^pSi is dominated by contributions from the t₂ symmetry SiO bonding orbital and σ^pO is dominated by contributions from the t₂ symmetry O 2p non-bonding orbital.     

KHSO4 · H2O/SiO2‐Catalyzed,One‐Pot,Solvent‐Free Synthesis of Pyrazolines,Tetrahydrocarbozoles and Indoles using Microwave Irradiation

A new high‐yielding, operationally simple, solvent‐free, and mild method for preparation of pyrazolines, tetrahydrocarbazoles, and indoles has been developed using KHSO₄ · H₂O impregnated on SiO₂. The reactions have been probed under microwave irradiation (MWI), and ultrasonic and thermal conditions, employing different solid supports. The data revealed that KHSO₄ · H₂O impregnated on SiO₂ under MWI provides the best yields in a shorter time under solvent‐free reaction conditions.     

Solubility of 13 nonpolar gases in deuterium oxide at 15–45°C and 101.325 kPa. Thermodynamics of transfer of nonpolar gases from H2O to D2O

Using a computer controlled version of the Ben-Naim and Baer apparatus, the solubilities of He, Ne, Ar, Kr, H₂, D₂, N₂, O₂, CH₄, C₂H₆, C₃H₈, CF₄, and SF₆ in D₂O (and the solubility of CF₄ in H₂O) were determined at four temperatures in the range 288 to 318 K and at a partial pressure of gas of 101.325 kPa. The precision of the measurements was 0.3–1.0%. The experimental data were processed using rigorous thermodynamic methods and were fitted to the Clarke-Glew-Weiss equation. Changes in the thermodynamic properties on solution were calculated from the smoothing equations. Scaled-particle theory (SPT) was used to determine the Lennard-Jones (6,12) pair potential parameters for D₂O: =0.275 nm and /k=83.4 K. Experimental mole fraction solubilities and thermodynamic functions at 298.15 K were compared with results calculated using the SPT. The thermodynamic transfer functions of gases from H₂O to D₂O were calculated. The changes induced by the solvation process on the structure of water were estimated from the Gibbs energy of transfer and the difference in the hydrogen bond energies for D₂O and H₂O.     

Characterization of Hydrophobic SiO2 Powders Prepared by Surface Modification on Wet Gel

Hydrophobic porous silica has been prepared by surface modification of TEOS (tetraethylorthosilicate) wet gel with 6 and 12 vol.% of TMCS (trimethylchlorosilane). We characterized the products by using FT-IR, TGA, DTA, N₂ adsorption/desorption, contact angle and SEM. Surface silanol groups of the gel were widely replaced by–Si(CH₃)₃ to result in a hydrophobic SiO₂ powder as confirmed by contact angle measurements with H₂O, 1-butanol and ethanol. The modified dried gels had a surface area of 950–1000 m²/g (average pore size 120 Å), compared to the non-modified surface which had a surface area of 690 m²/g (average pore size 36 Å). The adsorption/desorption isotherm curves indicated they had similar pore characteristics as aerogels prepared by the supercritical drying process.     

A New Practical Route to ZSM‐5 Nanoparticles and Optimization of Synthetic Parameters through D‐optimal Design of Experiments

A D‐optimal experimental design with three levels of SiO₂/Al₂O₃, template/SiO₂, H₂O/SiO₂, Na₂O/SiO₂ and TPABr/TPAOH ratio parameters has been used to optimize the experimental parameters by an analysis of variances (ANOVA). The effects of these ratios in the initial synthetic mixture on the size of the ZSM‐5 zeolite nanoparticles have been studied. XRD and FE‐SEM analyses were used to characterize synthetic samples. Fischer test results showed that H₂O/SiO₂ and TPABr/TPAOH ratios are the most and least effective parameters, respectively, in the range studied. The most important two‐way interaction variables were the interaction of template/SiO₂ and TPABr/TPAOH molar ratios. The average particle size was in the 34–79 nm range. Furthermore, a mathematical model for the synthesis of ZSM‐5 zeolite nanoparticles was derived using experimental results. The optimized gel composition is as follows: SiO₂/Al₂O₃₌91.20, template/SiO₂₌0.16, H₂O/SiO₂₌40.42, Na₂O/SiO₂₌0.0147 and TPABr/TPAOH=0.     

Surfactant-assisted hydrothermal crystallization of nanostructured lithium metasilicate (Li2SiO3) hollow spheres: II—Textural analysis and CO2-H2O sorption evaluation

In a previous work, the synthesis and structural-microstructural characterization of different nanocrystalline lithium metasilicate (Li₂SiO₃) samples were performed. Then, in this work, initially, a textural analysis was performed over the same samples. Li₂SiO₃ samples prepared with a non-ionic surfactant (TRITON X-114) presented the best textural properties. Therefore, this sample was selected to evaluate its water vapor (H₂O) and carbon dioxide (CO₂) sorption properties. Sorption experiments were performed at low temperatures (30-80 °C) in presence of water vapor using N₂ or CO₂ as carrier gases. Results clearly evidenced that CO₂ sorption on these materials is highly improved by H₂O vapor, and of course, textural properties enhanced the H₂O-CO₂ sorption efficiency, in comparison with the solid-state reference sample.     

Sol-gel coatings for chemical protection of stainless steel

Sol-gel thin coatings of ZrO₂, SiO₂, 70SiO₂-30TiO₂ and 88SiO₂-12Al₂O₃ compositions (mole %) have been prepared from sonocatalyzed sols and deposited by dip-coating technique on 316L stainless steel foils. The influence of the coatings on the chemical corrosion of the substrate has been measured through potentiodynamic polarization curves in aqueous 15% H₂SO₄ solution between 25 and 50°C. The values of the corrosion potential, polarization resistance and corrosion rate have been determined. Analysis of the data combined with scanning electron microscopy studies indicate that the films act as a geometric blocking against exposure to the corrosive media and increase the lifetime of the substrate up to a factor 8.5.     

Rh Inclusion in Sol-Gel SiO2. Effects of Rh Precursors on Metal Dispersion and SiO2-Rh Thermal Behavior

RhCl₃·nH₂O and [RhCl(C₂H₄)₂]₂ are used as precursors for the preparation of 1%Rh in sol-gel derived SiO₂. The gelling process of Si(OEt)₄ is carried out in the absence of solvent and under strong acid catalysis. The thermal behavior of Rh precursors, of SiO₂ gel and Rh-SiO₂ composites is independently studied by analysing organic species released at definite temperature intervals and concomitantly collecting infrared, XPS, TEM, XRD and porosity data. Results indicate that nanometric Rh particles may be obtained from [RhCl(C₂H₄)₂]₂, their dispersion being homogeneous, dense and stable up to 250°C, whereas RhCl₃·nH₂O affords less metallic dispersion with other crystalline Rh-species; in both cases, well-shaped Rh metal crystallites are obtained at 650°C. The different synthetic approaches used for the preparation of RhCl₃- and [RhCl(C₂H₄)₂]₂-derived samples, are invoked to account for the features of Rh dispersion obtained by mild temperature treatment. Moreover, the particular procedures for sol-gel SiO₂ synthesis are related to the high-temperature maintenance of great porosity and elevated specific surface area.     

多孔SiO_2·xH_2O负载RuB纳米粒子催化喹啉加氢反应

通过水解,聚乙烯吡咯烷酮(PVP)保护,NaOH刻蚀等方法制备了多孔及富含表面羟基的SiO2·xH2O负载的RuB催化剂RuB/SiO2·xH2O,并用X射线衍射(XRD)、X射线光电子能谱(XPS)、透射电子显微镜(TEM)、傅里叶变换红外(FT-IR)光谱和BET(Brunauer-Emmett-Teller)等手段对该催化剂进行了表征.结果表明该催化剂具有良好的抗中毒能力,在3.0MPa的H2压力和80℃的温和反应条件下,喹啉的转化率高于95%,生成1,2,3,4-四氢喹啉的选择性高于97%.并系统研究了表面羟基和溶剂对催化剂性能的影响,发现以水为溶剂时,RuB/SiO2·xH2O对喹啉加氢反应展示出较高的活性和对1,2,3,4-四氢喹啉较高的选择性,催化剂能够多次循环使用.这一体系的优异催化性能归属于载体表面羟基和水的协同作用.     

A Convenient Method for Selective Mono or Dinitration of Phenol under Mild Conditions

Nitrophenol can be obtained via nitrosation-oxidation of phenol with C₂H₂O₄.2H₂O, NaNO₂, and wet SiO₂ at room temperature in high yield. Direct mono or dinitration of phenol was also performed with C₂H₂O₄. 2H₂O, metal nitrates (ionic) and wet SiO₂ under different reaction conditions.     

Co或Ni促进的Cu/SiO2-Al2O3催化剂上丙三醇和苯胺气相合成3-甲基吲哚

对丙三醇和苯胺在Co或Ni促进的Cu/SiO2-Al2O3催化剂上气相合成3-甲基吲哚进行了研究.采用N2吸附、氢气程序升温还原(H2-TPR)、电感耦合等离子体(ICP)发射光谱、X射线衍射(XRD)、透射电子显微镜(TEM)、氨程序升温脱附(NH3-TPD)及热重(TG)分析等技术对催化剂进行了表征.结果表明,向Cu/SiO2-Al2O3催化剂加入钴或镍助剂改善了催化剂的催化性能,钴比镍更加有效.在催化剂Cu-Co/SiO2-Al2O3和Cu-Ni/SiO2-Al2O3上,反应第3 h,3-甲基吲哚收率分别达到47%和45%,而且催化剂经过6次再生收率仍能达到44%和42%.各种表征表明,向Cu/SiO2-Al2O3催化剂加入钴或镍助剂能增强铜和载体之间的相互作用,其结果不仅促进了铜粒子在载体表面的分散度,而且有效减少了反应过程中铜组分的流失.另外,加入钴或镍助剂还能减少催化剂的中强酸中心数,从而提高3-甲基吲哚的选择性,并且抑制积炭的形成.此外,钴助剂还能增加催化剂的弱酸中心数,促进3-甲基吲哚的生成.提出了金属铜与弱酸中心共同促进3-甲基吲哚合成的催化反应机理.     

Neue Verbindungen im System CaO/SiO2/CaCl2/H2O

New Compounds in the System CaO/SiO₂/CaCl₂/H₂O The hydrothermal formation of novel calcium silicate hydrates of compositions 5 CaO · 2 SiO₂ · CaCl₂ · 4 H₂O, 5 CaO · 2 SiO₂ · CaCl₂ · 2 H₂O and 4 CaO · 2 SiO₂ · CaCl₂ · H₂O from Ca₃SiO₅ and mixtures of CaO and SiO₂, respectively, in presence of calciumchloride at 200°–350 °C is described. From molybdate-reaction, ²⁹Si MAS NMR, DTA and TG measurements it is concluded that these compounds are based on disilicate anions and are to be interpreted as calcium hydroxide disilicate chlorides.     

ZrO4/SiO2-Al2O3催化肉桂醛MPV转移加氢性能

以九水合硝酸铝（Al（NO₃）₃·9H₂O）与正硅酸乙酯（TEOS）为前驱盐,采用溶胶-凝胶法制备一系列不同Al₂O₃含量的SiO₂-Al₂O₃复合氧化物,并通过浸渍硝酸氧锆引入ZrO₂,制备ZrO₂/SiO₂-Al₂O₃复合氧化物催化剂,考察催化剂在肉桂醛（CAL）MPV转移加氢中的催化性能,并结合N₂物理吸附、X射线粉末衍射（XRD）、傅里叶变换红外光谱（FTIR）、NH₃-程度升温脱附（NH₃-TPD）、Py-原位红外（Py-IR）等技术,研究催化剂结构、织构以及表面性质与其催化性能间的构效关系.研究表明,所制备的催化剂均以L酸为主,并含有少量B酸中心,这使得加氢产物以肉桂醇（COL）为主,并含有少量1-苯丙烯-2-丙基醚（CPE）.Al₂O₃含量不仅影响催化剂表面的酸中心数量,而且对催化剂的织构参数有较大影响.随Al₂O₃含量的增加,催化剂表面L酸与B酸中心均有所增加,而孔径则持续变小,这使得催化反应呈现CAL转化率先增加后减少、目标产物COL选择性先稍有减小后有所增加的趋势.在Si/Al比为2时,催化剂具有最优的催化性能,优化反应条件下,CAL转化率达96%,目标产物COL选择性达90%.     

Physico-chemical properties of metallosilicate supports and cobalt catalysts based on them

The specific surface and the porosity of silicate supports (SiO₂, ZrO₂ · SiO₂, CoO · SiO₂) were determined. The adsorption properties and the reducing ability of the catalysts containing 10 % Co were studied. The spectra of the thermo-programmed desorption of CO below 250°C possess two signals typical of the adsorption of the catalyst on the oxide and metal phases. The formation of liquid hydrocarbons from CO and H₂ is assumed to proceed at surface bifunctional centers.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 668–672, April, 1993.