Synthesis of V-MCM-41 by template-ion exchange method and its catalytic properties in propane oxidative dehydrogenation

Vanadium has been introduced to MCM-41 without collapse of the mesoporous structure by exchanging VO²+ ions in the aqueous solution with the template cations in the uncalcined MCM-41. This template-ion exchange (TIE) method provides tetrahedrally coordinated vanadyl species dispersed in the channel of MCM-41. Such synthesized V-MCM-41 shows higher catalytic activity in the oxidative dehydrogenation of propane than that prepared by direct hydrothermal method.     

Efficient isomerization of safrole by amino-grafted MCM-41 materials as basic catalysts

Design of base catalyst featuring large mesoporous surfaces allows performing base-catalysed reactions in the fields of production of perfumes. Post-synthesis grafting of organotrialkoxysilanes has effectively been applied to incorporate active organic functional groups onto the mesoporous silica surfaces. The novelty of our study is the use of mesoporous materials with different chemical compositions: silicate (MCM-41), aluminosilicate (AlMCM-41; Si/Al = 64) and niobosilicate (NbMCM-41; Si/Nb = 64) and consequently, different acidity, as supports for three aminopropylalkoxysilanes (APMS), [3-(2-aminoethylamino) propyl]trimethoxysilane (2APMS) and 3-[2-(2-aminoethylamino) ethylamino]propyltrimethoxysilane (3APMS). Isomerization of safrole to the corresponding thermodynamically stable isosafrole has been carried out on these amino-grafted MCM-41 materials. Maximum conversion of around 85% with a cis/trans ratio of 1/9 at 433 K in DMF as solvent was obtained. Isomerization is strongly dependent on the nature of the support and changed in the following order: APMS/AlMCM-41 > APMS/NbMCM-41 ? APMS/MCM-41. The nature of the amine chain is also responsible of the activity. The order of activity is APMS/AlMCM-41 > 2APMS/AlMCM-41 > 3APMS/AlMCM-41.     

Vanadium incorporated high surface area MCM-41 catalysts

High surface area MCM-41 (1452 m²/g) and V-MCM-41 materials were synthesized by a direct hydrothermal synthesis method. Characteristic XRD patterns, SEM and AFM photographs indicated no significant change in the morphology of MCM-41 by incorporation of vanadium. XPS and EDS results proved that incorporation of vanadium into the MCM-41 structure was successfully achieved when vanadyl sulfate hydrate was used as the vanadium source. However, use of ammonium vanadate as the vanadium source was not equally successful.     

Ni2P/Al-MCM-41催化剂的制备及其加氢脱硫性能

以硅酸钠为硅源、硫酸铝为铝源、十六烷基三甲基溴化铵（CTAB）作模板剂,采用共沸蒸馏与超声波分散技术相结合的方法制备了介孔分子筛Al-MCM-41。以Al-MCM-41为载体、硝酸镍和磷酸氢二氨为原料,采用超声波振荡、程序升温还原法制备了Ni₂P/Al-MCM-41催化剂,并对Al-MCM-41和Ni₂P/Al-MCM-41进行了傅里叶变换红外光谱、比表面积测定、X射线衍射、扫描电镜表征。考察了Ni₂P/Al-MCM-41催化剂对噻吩加氢脱硫的催化性能。结果表明：采用超声波制得的Al-MCM-41其比表面积、孔容和孔径明显高于常规搅拌制得的Al-MCM-41,共沸蒸馏制得的Al-MCM-41其比表面积、孔容和孔径高于未共沸蒸馏的Al-MCM-41;在反应时间为5 h、548 K、3.5 MPa条件下,Ni₂P/Al-MCM-41催化剂对噻吩加氢脱硫的转化率接近100%。     

Synthesis of non-porous and nanocrystalline lanthana-doped zirconia layers by MOCVD method at low temperatures and pressure

Amorphous and nanocrystalline lathana-doped zirconia layers were synthesized by the MOCVD method using La(tmhd)₃ and Zr(tmhd)₄ as reactants on planar and tubular quartz glass substrates. The synthesis temperature was in the range of 500–700 °C. The gas pressure in the CVD reactor was modified between 3 × 10³ and 6 × 10³ Pa. Argon and air were used as carrier gases. Air was also necessary for oxidation of carbon, which is a solid by-product of reactant pyrolysis. Other synthesis parameters were selected in order to obtain a value of the extended criterion Gr_x/Re_x² below 0.01. Then, laminar gas flow in the CVD reactor will be maintained. The surface, as well as the cross-section of deposited layers were observed using a scanning electron microscope (SEM). Their chemical composition was investigated by means of EDS analysis. XRD investigations on obtained layers were also performed. There was correlation between the chemical composition of reactants and obtained layers when the synthesis process was controlled by reactant diffusion to the substrate. The phenomenon of La³⁺ ion segregation in obtained layers was also observed. The layers exhibited good adhesion to the substrate.     

Phenol hydroxylation using Fe-MCM-41 catalysts

Highly ordered iron-containing mesoporous material, Fe-MCM-41, with 0.5–4 Fe/Si mol% loading was prepared and characterization was performed using XRD, SEM/TEM, EDS, N₂-sorption, and FT-IR and UV–vis spectroscopies. Fe-MCM-41 exhibited high catalytic activity in phenol hydroxylation using H₂O₂ as oxidant, giving phenol conversion of ca. 60% at 50 °C [phenol:H₂O₂ = 1:1, water solvent]. Effects of Fe contents in Fe-MCM-41 and catalyst concentration, temperature, solvent used, phenol/H₂O₂ mole ratios and H₂O₂ feeding method, and catalyst calcination temperature on conversion profiles were examined. Catalyst recycling was performed to investigate the extent of potential metal leaching. Comparisons in performance were also made using nano-sized Fe₂O₃ particles and Fe-salt impregnated MCM-41 as catalyst. Catechol to hydroquinone in product ratio was close to 2:1 in accordance with a free radical reaction scheme involving Fe²⁺/Fe³⁺ redox pair and the larger amount of Fe species always achieved the given phenol conversion at a shorter reaction time. As the calcination temperature increases from 400 to 800 °C increasing amount of Fe species came out from the MCM-41 framework. Both tetrahedral Fe and extra-framework Fe species were found catalytically active, but high dispersion of Fe species achieved in Fe-MCM-41 was an advantage.     

Sn修饰SBA-15、MCM-41催化剂的制备及顺酐酯化性能

以SBA-15和MCM-41分子筛为载体,负载无水四氯化锡,制备了SnCl4-SBA-15和SnCl4-MCM-41催化剂,考察了不同锡与硅物质的量比对催化顺酐与正丁醇酯化反应的影响。结果表明,SnCl4-SBA-15表现出比SnCl4-MCM-41更高的催化性能,顺酐转化率为99.8%,副产物较少,马来酸二丁酯的产率最高可达91.3%。采用X射线衍射、N₂物理吸附、傅立叶红外光谱和紫外-可见漫反射技术对催化剂进行表征,结果显示, SnCl₄-SBA-15具有较高的比表面积,较大的孔容和孔径,更有利于催化反应的进行。     

用MOCVD方法制备TIO2薄膜：工艺及进展

本文概述了用金属有机物化学气相沉积（ＭＯＣＶＤ）的方法制备了ＴＩＯ２薄膜的原理工艺过程用工艺特点，并指出了最新研研进展和存在的问题以今后及发展方向。     

BaTiO3薄膜的MOCVD方法制备及进展

本文概述了用金属有机物化学气相沉积（ＭＯＣＶＤ）方法制备ＢａＴｉＯ３薄膜的原理和特点,着重介绍低压ＭＯＣＶＤ、等离子体增强ＭＯＣＶＤ和光辅助ＭＯＣＶＤ三种技术在ＢａＴｉＯ３薄膜制备中的应用,并指出了最新进展进行、存在的困难和今后的发展趋势。     

TiO2纳米粉末的热壁低压MOCVD方法制备

采用热壁低压ＭＯＣＶＤ方法制备了ＴｉＯ２纳米粉末。研究了收集区、载气流量和氧化气流量对ＴｉＯ２纳米粉末的晶体结构、平均晶粒尺寸和粒度分布的影响规律。采用Ｒａｍａｎ散射、Ｘ射线衍射和航向电子显微镜等技术对ＴｉＯ２纳米粉末进行了表征。     

Deposition of gadolinia-doped ceria layers by MOCVD at low temperatures

Electrolyte layers of Gd₂O₃-doped CeO₂ were synthesized by MOCVD with the use of Ce(tmhd)₄ and Gd(tmhd)₃ as reactants in the temperature range of 500–800 °C at reduced pressure. Ar and air were carrier gases. The layers were deposited on the inner surfaces of quartz glass tubes and flat glass substrates. The obtained layers were non-porous and smooth. The layers synthesized at temperature of 500 °C were amorphous. At higher synthesis temperatures, the deposited layers were nanocrystalline. The higher the synthesis temperature, the larger the grains. When the synthesis process was controlled by mass diffusion to the substrate, then a correlation between the chemical composition of reactants and chemical composition of the synthesized layer can be determined. The obtained layers were also examined by scanning electron microscopy, X-ray analysis and UV‐VIS spectroscopy. Additionally, the chemical composition of the synthesized layers was investigated using an EDS analyzer.     

Structural and catalytic properties of Ti–MCM-41 synthesised at room temperature up to high Ti content

A study of the pore structural properties and catalytic activity of MCM-41 containing titanium, prepared by direct synthesis at ambient temperature and pressure, using tetraethoxysilane, titanium alcoxides, cationic surfactants and ammonia is presented. The influence of different metal sources (titanium ethoxide, isopropoxide or n-butoxide), alcohols (ethanol or propan-2-ol), metal content (2  Si/Ti  100) and surfactants (tetra-, hexa- or octadecyltrimethylammonium bromide) is considered. The materials were characterised by X-ray diffraction, nitrogen adsorption at 77 K and diffuse reflectance UV–Vis spectroscopy. The catalytic activity was evaluated in the model reaction of oxidation of cyclohexene with anhydrous tert-butylhydroperoxide, for representative samples. It is concluded that this method allows the preparation in a short period of time of well structured and catalytically active Ti–MCM-41. Down to Si/Ti = 10 the materials have high pore volumes and very uniform pore size, with highest conversion and excellent selectivity demonstrated in the compositional range 30  Si/Ti  100, corresponding to materials containing predominantly isolated and tetracoordinated Ti. The increase in Ti content to Si/Ti ratios of 10 and 5 implied a reduction both in conversion and selectivity, although the MCM-41 structure was still observed for Si/Ti = 2.     

Selective hydroxylation of phenol employing Cu–MCM-41 catalysts

We studied the oxidation reaction of phenol in aqueous and acetonitrile media under mild conditions, employing Cu-modified MCM-41 mesoporous catalysts. The stability of the catalysts under reaction conditions was confirmed by XRD, UV–VIS and FTIR techniques. Results obtained indicate that the selective oxidation of phenol with H₂O₂ by a radical substitution mechanism produces three main reaction products: catechol, hydroqinone and benzoquinone.     

Cerium-containing MCM-41 materials as selective acylation and alkylation catalysts

The synthesis of Ce–MCM-41, Al–MCM-41 and Ce–Al–MCM-41-type mesoporous materials was carried out hydrothermally by refluxing the gel with magnetic stirring under atmospheric pressure for 24–36 h. The samples were characterized thoroughly in order to obtain the structural and textural properties, which reveal the presence of well-ordered M41S-type materials. The Ce–MCM-41 samples were used for catalytic acylation of alcohols, thiols, phenols and amines show good activity and selectivity including high chemoselectivity towards selective monofunctional acylation of bifunctional compounds. Quite importantly the acylation of bulky molecules such as cholesterol, ergesterol and β-sitosterol could be achieved using Ce–MCM-41 as solid catalyst. The presence of Ce along with Al in Ce–Al–MCM-41 was found to have synergistic effect as Ce–Al–MCM-41samples were more active catalysts for alkylation of naphthalene compared to either Ce–MCM-41 or Al–MCM-41 with comparable Si/Al or Si/Ce molar ratio.     

Propylene epoxidation over Ti/MCM-41 catalysts prepared by chemical vapor deposition

Ti-containing mesoporous catalysts were prepared by chemical vapor deposition (CVD) of TiCl₄ on silica MCM-41 in the 700–900 °C temperature range. These samples were characterized (with XRD, ICP, nitrogen adsorption, FT-IR, ESCA, and TEM) and evaluated for the epoxidation of propylene with two alkyl hydroperoxides. The increase of CVD temperature resulted in the decrease of titanium content, catalyst hydroxyl population, crystallinity, and surface area. Catalyst selectivity to the desired product – propylene oxide – was highly sensitive to the deposition temperature. The best Ti/MCM-41 catalyst was prepared at the temperature of 800 °C, which had the maximum propylene oxide yield of 94.3%.     

Characteristics of Al-MCM-41 supported Pt catalysts: effect of Al distribution in Al-MCM-41 on its catalytic activity in naphthalene hydrogenation

Naphthalene hydrogenation was carried out in a high-pressure batch reactor over platinum catalysts supported on Al-MCM-41 where aluminum was incorporated through two different methods: a direct sol–gel method (Pre) and post-synthetic grafting method (Post). The catalytic reaction was also performed in the presence of dibenzothiophene to investigate the sulfur tolerance. The hydrogenation activity, selectivity and the sulfur tolerance strongly depended on the acidic nature of Al-MCM-41 support. It was suggested that the acid sites of Al-MCM-41-Post be more accessible than those of Al-MCM-Pre due to different aluminum distribution within the pore wall. The naphthalene and tetralin conversion increased with the acid amount of the supports in Pt/Al-MCM-41 catalysts. The acid sites in bifunctional catalysts seemed to contribute to alternative pathway by the spillover hydrogen in the acid–metal interfacial region for naphthalene hydrogenation, since the metal dispersions were kept constant for Pt/Al-MCM-41 catalysts. The trans-decalin selectivity generally increased with temperature or acid amount. The acid sites seemed to enhance the sulfur tolerance of supported platinum catalysts due to the electron-deficient state of metal.     

Characterization of single crystalline a-TiO2 films on MgAl2O4(100) substrates by MOCVD

Anatase phase TiO₂ (a-TiO₂) films have been deposited on MgAl₂O₄(100) substrates at the substrate temperatures of 500–650 °C by the metal organic chemical vapor deposition (MOCVD) method using tetrakis-dimethylamino titanium (TDMAT) as the organometallic (OM) source. The structural analyses indicated that the TiO₂ film prepared at 600 °C had the best single crystalline quality with no twins. The out-of-plane and in-plane epitaxial relationships of the film were a-TiO₂(001)||MgAl₂O₄(100) and TiO₂[100]||MgAl₂O₄[100], respectively. A uniform and compact surface with stoichiometric composition was also obtained for the 600 °C-deposited sample. The average transmittance of all the TiO₂ films in the visible range exceeded 91% and the optical band gap of the films varied from 3.31 to 3.41 eV.     

微波固相法制备MCM-41固定 氯化铝催化剂及其催化性能

采用微波固相法制备了MCM-41固定氯化铝固体酸催化剂。以合成乙酸正戊酯为探针反应,考察了氯化铝不同负载量、反应时间、微波功率对其催化性能的影响。结果表明,氯化铝负载量为6 mmol/g、反应时间为 15 min、微波功率为750 W时,所制得的催化剂活性最好,其酯化率可达92.7%。     

Structural and optical studies of CdS and CdS:Ag nano needles prepared by a SILAR method

Nano-crystalline CdS and Ag-doped CdS films are deposited on glass substrate by a SILAR technique at room temperature with cationic precursors of cadmium nitrate and silver nitrate, and anionic precursor of sodium sulfide with different S:Cd ratio in starting solutions. In order to fabricate samples, substrates were taken in the solutions with determined duration and immersion cycles. To investigate the structural and morphological characteristics of the samples XRD analysis and SEM were used. The X-ray diffraction patterns show that the CdS samples have cubic crystal structure with preferential orientation along the (111) plane and CdS:Ag samples have hexagonal crystal structure with preferential orientation along the (002) plane. Also the peak intensity of XRD patterns of CdS increases with increasing the number of immersion cycles. Optical reflection of the layers is measured with a spectrophotometer and their optical absorption coefficient and band gaps are calculated. The band gap energy of Ag-doped samples decreases respect to CdS samples. It seems that silver doping creates intermediate levels in the energy gap and this causes decreasing of energy gap. Making samples with different S:Cd ratio demonstrates that the sample with 3:1 ratio has highest peak intensity in the XRD pattern and best stoichiometry. It is also observed that with increasing S:Cd ratio, the band gap energy of the samples decreases.     

Vapor phase propylene epoxidation over Au/Ti-MCM-41 catalysts prepared by different Ti incorporation modes

Ti-containing MCM-41 supports were prepared by: (a) hydrothermal crystallization; (b) post-synthesis grafting; and (c) two-step Ti incorporation—hydrothermal incorporation followed by post-synthesis grafting. XRD revealed little change in crystallinity and long range order of MCM-41 phase after Ti incorporation by different methods. UV-Vis spectra show the presence of tetrahedral Ti sites at lower Ti contents (upto 4.5 mol%), but aggregated titania formation could be observed at higher Ti loadings (>4.5 mol%). The samples exhibit surface areas and pore volumes in the mesoporous range. Vapor phase epoxidation of propene using H₂ and O₂ was carried out over these supports after Au deposition by deposition-precipitation (DP) method. The Ti-MCM-41 supports prepared by two-step Ti incorporation (with up to 4.5 mol% input Ti), which probably have more number of isolated Ti sites, showed higher catalytic activity than Ti-MCM-41 prepared by one-step Ti incorporation method, at comparable propylene oxide selectivities and hydrogen efficiencies. The former catalyst also deactivates more slowly than the latter ones, probably due to a decrease in the number of silanol sites (those responsible for deactivation) due to grafted Ti.