Room temperature synthesis of Ti-SBA-15 from silatrane and titanium-glycolate and its catalytic performance towards styrene epoxidation

A novel room temperature sol–gel synthesis of Ti-SBA-15 is described using moisture stable silatrane and titanium glycolate precursors, and poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymer (EO₂₀PO₇₀EO₂₀) as the structure directing agent. Catalyst performance was optimized by systematically investigating the influence of acidity, reaction time and temperature, and titanium loading. Small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) showed well-ordered 2D mesoporous hexagonal structures, while N₂ adsorption/desorption measurements yielded high surface areas (up to 670 m²/g), with large pore diameters (5.79 nm) and volumes (0.83 cm³/g). Diffuse reflectance UV–visible spectroscopy (DRUV) was found that tetravalent titanium as Ti⁴⁺O₄ tetrahedra were incorporated in the framework through displacement of Si⁴⁺O₄ after calcination (550°C/6 h) to loadings of 7 mol% Ti without perturbation of the ordered mesoporous structure, or decoration by extra-framework anatase containing Ti⁴⁺O₆ octahedra. The catalytic activity and selectivity of styrene epoxidation using hydrogen peroxide (H₂O₂) showed that the conversion of styrene increases significantly at higher titanium contents. The only products of this reaction were styrene oxide and benzaldehyde, with selectivity of 34.2 and 65.8%, respectively, at a styrene conversion of 25.8% over the 7 mol% Ti-SBA-15 catalyst. Beyond this titanium loading, anatase is deposited on the framework and catalytic activity degrades. The performance of the new catalyst is also shown to be superior to conventional materials produced by incipient wetness impregnation where Ti resides on the surface of SBA-15, giving a styrene conversion of 11.9% under identical reaction conditions.     

Highly efficient oxidative cleavage of alkenes and cyanosilylation of aldehydes catalysed by magnetically recoverable MIL‐101

The catalytic activity of magnetically recoverable MIL‐101 was investigated in the oxidation of alkenes to carboxylic acids and cyanosilylation of aldehydes. MIL‐101 was treated with Fe₃O₄ and the prepared catalyst was characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, N₂ adsorption measurements, field emission scanning electron microscopy, energy‐dispersive X‐ray spectroscopy and inductively coupled plasma analysis. The catalytic active sites in this heterogeneous catalyst are Cr³⁺ nodes of the MIL‐101 framework. This heterogeneous catalyst has the advantages of excellent yields, short reaction times and reusability several times without significant decrease in its initial activity and stability in both oxidation and cyanosilylation reactions. Its magnetic property allows its easy separation using an external magnetic field.     

Macro-kinetics of styrene oxidation catalyzed by Co<Superscript>2+</Superscript>-exchanged X

The macro-kinetics and pathway of styrene oxidation catalyzed by Co²⁺-exchanged X, using O₂ as oxidant, were investigated. The effects of external diffusion, internal diffusion, the styrene concentration, O₂ pressure, the catalyst concentration and the reaction temperature on the styrene oxidation reaction rate were examined. The results showed that the reaction rate of styrene oxidation was 0.19 order with respect to the styrene concentration, 0.64 order with respect to O₂ pressure, and zero to first order with respect to the different catalyst concentration. The calculated activation energy for this reaction was 13.79 kJ/mol. On the other hand, the three products in the styrene oxidation reaction were, respectively, used as the reactant to examine the reaction pathway of styrene oxidation. The results revealed that styrene oxidation reaction occurred as two parallel reactions. One was the production of styrene oxide and the other was the production of benzaldehyde and formaldehyde with former partially oxidized to benzoic acid and the latter mostly oxidized to O₂ and H₂O. Published in Russian in Kinetika i Kataliz, 2009, vol. 50, No. 2, pp. 212–217. The article is published in the original.     

One pot synthesis of chromium incorporated SBA-16 under acid medium-Application in the selective oxidation of benzyl alcohol derivatives

Cr-SBA-16 mesoporous silica heterogeneous catalysts (Si/Cr = 7, 14, and 28) were successfully synthesized by one-pot hydrothermal method at low acidic medium. The catalysts were characterized by means of X-ray diffraction (XRD), N₂ adsorption-desorption at 77 K, Fourier Transform Infrared (FTIR), X-ray photoelectron (XPS) and Diffuse Reflectance UV–Vis (DRS) Spectroscopies, Thermogravimetric analysis (TGA), Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) techniques. Herein, Cr-SBA-16 catalysts are evaluated in the selective catalytic oxidation of benzyl alcohol derivatives using H₂O₂ as oxidant. From XPS and UV–Vis (DRS) spectroscopies the molar ratios between Cr⁶⁺/Cr³⁺ are found to increase versus chromium loading in the following order: Cr-SBA-16(28) < Cr-SBA-16(14) < Cr-SBA-16(7). Hence the highest Cr⁶⁺ in tetrahedrally environment is observed for Si/Cr = 7. We demonstrated for the first time that the selective catalytic oxidation of benzyl alcohol (BzOH) using H₂O₂ over Cr-SBA-16 occurs through noncompetitive adsorption mechanism and the reaction is pseudo-first order to BzOH. The activity of the reaction depends on the symmetry of chromium species, herein, high activity is observed for tetrahedral chromium species in Cr-SBA-16(7). The absence of any chromium ions in the filtrate shows no chromium leaching from the silica framework.     

介孔Ag_2S固载锰卟啉催化氧化环己烷性能研究

为了充分发挥5,10,15,20-四(4-吡啶基)锰卟啉(Mn TPyP)的催化活性和效率,用介孔硫化银对Mn TPyP进行轴向配位,形成了介孔硫化银固载5,10,15,20-四(4-吡啶基)锰卟啉(Mn TPyP/mp-Ag_2S)纳米孔仿生催化材料,用多种光谱技术对其进行表征.催化材料中S~(2-)与阳离子Mn~(3+)之间有很强的轴向配位作用,这使得催化材料催化氧化环己烷的活性大幅提高,环己烷转化率和醇酮产率分别提高了46.9%和29.6%.催化材料使用了5次后,其催化性能几乎没有下降,这归因于催化材料中强的轴向配位作用和纳米空腔结构功能作用的结果.     

SBA-15负载的Cu(Ⅱ)席夫碱配合物催化的苯乙烯氧化反应制备苯甲醛

采用一步法将原硅酸四乙酯与3-氨丙基三乙氧基硅烷在表面活性剂P123作用下,酸性共水解制备出氨基功能化的介孔分子筛SBA-15(NH2-SBA-15),再利用其中氨基与水杨醛的缩合反应制备SBA-15固载的席夫碱,该席夫碱与Cu(NO3)2溶液反应最终制成固定于SBA-15的Cu(II)席夫碱配合物多相催化剂Cu-SBA-15.采用X射线衍射、红外光谱仪、紫外可见分光光度计、场发射电镜、透射电镜、N2吸附-脱附、元素分析、原子发射光谱和热重分析对催化剂进行了表征,并将此催化剂用于无有机溶剂条件下催化氧化苯乙烯制备苯甲醛,考察了反应时间、反应温度、H2O2用量、水的用量、催化剂用量对反应的影响.当反应温度为100°C,反应时间8 h,H2O2与苯乙烯的摩尔比为2:1,不额外添加溶剂,且催化剂用量为3.8 wt%时,苯乙烯的转化率最高为84.4%,苯甲醛选择性为83.9%,催化剂的TOF值为261.1 h–1,并且重复使用3次后活性没有明显下降.规则的孔道、较大的比表面积以及分布均匀的活性中心可能是催化剂活性提高的原因.     

三核钨簇合物-V2O5催化剂对苯乙烯氧化反应的催化

本文研究了三核钨簇合物［W₃O₂(CH₃CO₂)₆(H₂O)₃］Br₃·2H₂O与一些物质组成的二元催化剂对苯乙烯氧化反应的催化作用,结果表明：钨簇合物-V₂O₅催化剂对苯乙烯氧化反应的催化效果特别显著,而且在反应前后其重量、结构及催化活性基本不变,可以多次回收重复使用。对影响钨簇合物-V₂O₅催化剂催化性能的几个因素进行了讨论,测定了催化剂及其吸附氧气的红外光谱,说明钨簇合物及V₂O₅可以与O₂形成分子氧配合物及超氧(O^-₂)配合物。     

Tungstate supported mesoporous silica SBA‐15 with imidazolium framework as a hybrid nanocatalyst for selective oxidation of sulfides in the presence of hydrogen peroxide

In this work, a new heterogeneous catalyst (SBA‐15/Im/WO₄^2?) was prepared, and then its performance in the oxidation of organic sulfides was studied (using 30% H₂O₂ as green oxidant under neutral reaction conditions). This organic–inorganic hybrid mesoporous material was characterized by various techniques, such as FT‐IR, inductively coupled plasma, X‐ray powder diffraction, high‐resolution‐transmission electron microscopy, N₂ adsorption–desorption and thermogravimetric analysis. The catalyst was also applied to the selective oxidation of various sulfides. The hybrid catalyst was easily recovered, and was very stable and retained good activity for at least five successive runs without any additional activation. Moreover, there was no remarkable decrease in the activity and selectivity of the catalyst. The products could be easily isolated by just removing the solvent after filtering the catalyst. The yields of the catalytic productions through this catalyst were in the range from 75% to 97%.     

Dual-template synthesis of defect-rich mesoporous Co3O4 for low temperature CO oxidation

CO oxidation is a benchmark in heterogeneous catalysis for evaluation of redox catalysts due to its practical relevance in many applications and the fundamental problems associated with its very high activity at low temperatures. Among which, Co₃O₄ is one of the most active non-precious metal catalysts. Exposed crystal planes and cobalt sites are considered to be important for its high catalytic activity. Herein, we demonstrate an enhanced CO oxidation activity by a defect-rich mesoporous Co₃O₄ that prepared by a designed dual-template method. Two different kinds of silicas are used as hard-templates at the same time, resulting in a defect-rich mesoporous Co₃O₄ with a surface area as high as 169 m²/g. This catalyst exhibited a very high catalytic activity for low temperature CO oxidation with a light-off temperature at −73 ^oC under the space velocity of 80,000 mL h^-1 g_cat^-1. Further studies reveal that the high surface area promotes the lattice oxygen mobility, surface rich of Co²⁺ species and active oxygen species are crucial for the high catalytic activity. Moreover, the dual-template approach paves a way towards the design and construction of high-surface-area mesoporous metal oxides for various applications.     

Hydrophobic Modification of Pd/SiO2@Single‐Site Mesoporous Silicas by Triethoxyfluorosilane: Enhanced Catalytic Activity and Selectivity for One‐Pot Oxidation

To enhance the catalytic activity in a selective one‐pot oxidation using in‐situ generated H₂O₂, a hydrophobically modified core–shell catalyst was synthesized by means of a simple silylation reaction using the fluorine‐containing silylation agent triethoxyfluorosilane (TEFS, SiF(OEt)₃). The catalyst consisted of a Pd‐supported silica nanosphere and a mesoporous silica shell containing isolated Ti^IV and F ions bonded with silicon (Si?F bond). Structural analyses using XRD and N₂ adsorption–desorption suggested that the mesoporous structure and large surface area of the mesoporous shells were retained even after the modification. During the one‐pot oxidation of sulfide, catalytic activity was enhanced significantly by increasing the amount of fluorine in the shell. A hydrophobic surface enhanced adsorption of the hydrophobic reactant into the mesopore, while the less hydrophobic oxygenated products efficiently diffused into the outside of the shell, which improved the catalytic activity and selectivity. In addition, the present methodology can be used to enhance the catalytic activity and selectivity in the one‐pot oxidation of cyclohexane by using an Fe‐based core–shell catalytic system.     

Cobalt Element Effect of Ternary Mesoporous Cerium Lanthanum Solid Solution for the Catalytic Conversion of Methanol and CO2 into Dimethyl Carbonate

A citric acid ligand assisted self-assembly method is used for the synthesis of ternary mesoporous cerium lanthanum solid solution doped with metal elements (Co, Zr, Mg). Their textural property was characterized by X-ray diffraction, transmission electron microscopy, N₂ adsorption-desorption, X-ray photoelectron spectroscopy and TPD techniques, and so on. The results of catalytic testing for synthesis of dimethyl carbonate (DMC) from CH₃OH and CO₂ indicated that the DMC yield reached 316 mmol/g on Ce-La-Co solid solution when the reaction temperature was 413 K and the reaction pressure was 8.0 MPa. It was found that Co had synergistic effect with La and Ce, doping of Co on the mesoporous Ce-La solid solution was helpful to increase the surface area of the catalyst, promote CO₂ adsorption and activation, and improve the redox performance of solid solution catalyst. The conversion of Co²⁺ to Co³⁺ resulted in the continuous redox cycle between Ce⁴⁺ and Ce³⁺, and the oxygen vacancy content of the catalyst was increased. Studies have shown that the catalytic performance of Ce-La-Co solid solution is positively correlated with oxygen vacancy content. On this basis, the reaction mechanism of DMC synthesis from CO₂ and CH₃OH on the catalyst was speculated.     

Cu(II) immobilized on mesoporous organosilica as an efficient and reusable nanocatalyst for one‐pot Biginelli reaction under solvent‐free conditions

Cu(II) immobilized on mesoporous organosilica nanoparticles (Cu²⁺@MSNs‐(CO₂^?)₂) has been synthesized, as a inorganic–organic nanohybrid catalyst, through a post‐grafting approach. Its characterization is carried out by Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Energy dispersive X‐ray (EDX), Thermogravimetric/differential thermal analyses (TGA‐DTA), and Nitrogen adsorption–desorption analysis. Cu²⁺@MSNs‐(CO₂^?)₂ exhibits high catalytic activity in the Biginelli reaction for the synthesis of a diverse range of 3, 4‐dihydropyrimidin‐2(1H)‐ones, under mild conditions. The anchored Cu(II) could not leach out from the surface of the mesoporous catalyst during the reaction and it has been reused several times without appreciable loss in its catalytic activity.     

Salen-decorated Periodic Mesoporous Organosilica: From Metal-assisted Epoxidation to Metal-free CO2 Insertion

We clicked a salen ligand onto a thiol-ethane bridged periodic mesoporous organosilica (Salen-PMO) using a photo-initiated thiol-ene click reaction. This process resulted in a covalently bonded salen ligand on the PMO material. The final BET surface area amounts 511 m²/g and the pore size diameter is approximately 7 nm. The functionalized PMO material showed an excellent carbon dioxide uptake capacity of 1.29 mmol/g at 273 K and 1 bar. More importantly, by coordinating a MoO₂²⁺ complex onto the Salen-PMO material, we obtained a heterogeneous catalyst with a good catalytic performance for the epoxidation of cyclohexene. The catalyst was highly reusable, as no decrease in its activity was observed for at least four runs (99% conversion). Finally, the metal-free Salen-PMO showed an exceptional catalytic performance in the cycloaddition of CO₂ to epoxides. The obtained results clearly demonstrate the versatility of the Salen-PMO material not only as metal-free catalyst but also as a support material to anchor metal complexes for specific catalytic applications. With the same catalytic platform, we were able to firstly create epoxides out of alkenes, and subsequently turn these epoxides into cyclic carbonates, consuming CO₂.     

多孔材料负载金催化剂的制备与应用*

本文综述了微孔材料和介孔材料负载型金催化剂的制备、表征与应用研究的最新进展,从多孔载体的选择（氧化物、微孔分子筛、介孔氧化物、介孔分子筛和介孔碳材料）、金的最新负载方法（沉积-沉淀法、溶胶-凝胶法、原位法/一步法和化学气相沉积法）与表征及其催化性能（一氧化碳低温氧化、氢气/氧气直接合成过氧化氢、直接合成环氧丙烷和有机物的选择性氧化）等方面详尽地评述了微孔材料和介孔材料负载型金催化剂研究概况。同时,提出了多孔材料负载金催化剂存在的一些问题,并展望了其研究和发展的方向。     

Efficient Selective Oxidation of Aromatic Alkanes by Double Cobalt Active Sites over Oxygen Vacancy-rich Mesoporous Co3O4

The development of efficient catalyst for selective oxidation of hydrocarbon to functional compounds remains a challenge. Herein, mesoporous Co₃O₄ (mCo₃O₄-350) showed excellent catalytic activity for selective oxidation of aromatic-alkanes, especially for oxidation of ethylbenzene with a conversion of 42 % and selectivity of 90 % for acetophenone at 120 °C. Notably, mCo₃O₄ presented a unique catalytic path of direct oxidation of aromatic-alkanes to aromatic ketones rather than the conventional stepwise oxidation to alcohols and then to ketones. Density functional theory calculations revealed that oxygen vacancies in mCo₃O₄ activate around Co atoms, causing electronic state change from Co³⁺_(Oh)→Co²⁺_(Oh). Co²⁺_(Oh) has great attraction to ethylbenzene, and weak interaction with O₂, which provide insufficient O₂ for gradual oxidation of phenylethanol to acetophenone. Combined with high energy barrier for forming phenylethanol, the direct oxidation path from ethylbenzene to acetophenone is kinetically favorable on mCo₃O₄, sharply contrasted to non-selective oxidation of ethylbenzene on commercial Co₃O₄.     

单双核金属配合物选择性催化氧化对甲氧基苦杏仁酸

制备了以铜、钴、锰为中心离子的三种单核金属配合物L¹Cu、L¹Co、L¹Mn (L¹=N,N'-(2-羟乙基)丙二酰胺)和三种双核金属配合物L²Cu、L²Co、L²Mn (L²=N,N'-{2-(2-羟乙基氨基)乙基}丙二酰胺). 研究发现在缓冲溶液中六种金属配合物能将对甲氧基苦杏仁酸(4-MMA)高选择性地氧化成对甲氧基苯甲醛(AAD)以及少量对甲氧基苯甲酸(4-MBA), AAD的选择性(S)大于96%. 然而不同的催化体系在反应速率上表现了很大的不同: 铜金属配合物的催化活性最好; 双核配合物表现出更高的催化效率. 研究了酒石酸(TA)、磷酸(H₃O₄)、醋酸(HAc)三种缓冲溶液体系对L¹Cu催化H₂O₂氧化4-MMA反应的影响, 结果表明缓冲溶液种类对反应速率和选择性影响很大.研究了35℃时弱酸性条件(pH值从2.5到4.5的范围内)在酒石酸缓冲溶液中六种金属配合物催化H₂O₂氧化4-MMA的动力学, 计算出不同pH值条件下催化反应的表观反应速率常数k_obs, 并且讨论了pH值对催化反应的影响.     

The effect of encapsulated Zn-POM on the catalytic activity of MIL-101 in the oxidation of alkenes with hydrogen peroxide

Zinc monosubstituted Keggin heteropolyanion [PZnMo₂W₉O₃₉]^5? was electrostatically bound to nanocages of MIL-101 polymer matrix. The Zn-POM@MIL-101 catalyst was characterized by XRD, N₂ adsorption, atomic absorption (AAS), and FT-IR spectroscopic methods. The catalytic activity of the new composite material, Zn-POM@MIL-101, was assessed in the oxidation of alkenes using aqueous hydrogen peroxide as oxidant. Zn-POM@MIL-101/H₂O₂ catalytic system demonstrated good catalytic activity in the oxidation reactions. Zn-POM@MIL-101 was reusable for three catalytic cycles. While the MIL-101 matrix is an active catalyst in these oxidation reactions, the presence of Zn-POM significantly changed the selectivity and reaction times.     

Catalytic properties of Fe-HMS materials in the phenol oxidation

Iron-incorporated mesoporous silica material Fe-HMS-50 (the Si/Fe molar ratio in the precursor gel is 50) was synthesized at ambient temperature by using hexadecylamine as a template and characterized by chemical analysis and N₂ adsorption measurements. The catalytic performance of Fe-HMS was studied in the phenol hydroxylation and wet phenol oxidation with H₂O₂ at 313 K. The effect of pH, H₂O₂: PhOH molar ratio and stability of the catalyst on the oxidation process was investigated. In the phenol oxidation, the activity of the catalyst increases by increasing the acidity of the reaction mixture to pH 3.4 and the amount of leached iron species was 1.95 ppm. A recycling test indicates that the catalyst recovered by drying in air at 423 K suffered, after the first run, a 12.4% drop in the catalytic activity. Fe-HMS has high catalytic activity and selectivity to dihydroxybenzene in the phenol hydroxylation. Hydroquinone was found as the predominant product under these experimental conditions with small amounts of benzoquinone appearing at the end of the reaction.     

三维介孔氨基三亚甲基膦酸锆的合成及其担载铁催化剂的甲醛催化氧化活性

以氧氯化锆和氨基三亚甲基膦酸(ATMP)为原料合成了一种新型介孔材料氨基三亚甲基膦酸锆(NTAZP)。使用XRD、FTIR、TG-DTA和SEM等手段对所合成的介孔材料进行了结构表征和形貌分析。然后以NTAZP为载体,用Fe(NO3)3水溶液处理,得到担载Fe3+的氨基三亚甲基膦酸锆。研究结果表明,Fe3+被吸附到载体孔道中后,NTAZP结构未被破坏,Fe3+离子与NTAZP孔壁骨架上的N发生了配位作用。铁担载NTAZP(NTAZP-Fe3+)对甲醛氧化具有良好的催化活性,催化反应条件温和,催化剂稳定性良好。以载体NTAZP担载铁还避免了Fe3+进入水体,催化剂得以回收利用,避免造成二次污染。NTAZP-Fe3+是一种高效绿色的新型小分子醛类化合物氧化催化剂。     

High Catalytic Performance of Mesoporous Dual Brønsted Acidic Ternary Poly (Ionic Liquids) for Friedel‐Crafts Alkylation

A newfangled cross‐linked dual Brønsted acidic ternary mesoporous poly (ionic liquids)(MPILs) with mesoporous structure was successfully synthesized with divinylbenzene as cross linker, 1‐vinyl‐3‐butyl imidazole bromide and sodium p‐styrene sulfonate as functional group through an ordinary post‐modification method and anion exchange process. A sponge‐like mesoporous tunnel structure was observed and the obtained P (BVS‐SO₃H)‐SO₃CF₃ sample appeared a relatively high thermal stability, a large surface area (up to 286.8 m²/g) and great pore volume (0.73 cm³/g). The abundant dual acidic group of sulfonic acid and trifluoromethanesulfonic acid of the composite in the polymer framework impart Brønsted acidity. For the sake of demonstrating our claims, the sample has been used as a novel solid acid catalyst for the reaction of alkylation of o‐xylene with styrene to 1‐diphenylethane (PXE). Under optimal reaction conditions (reaction under 120 °C for 3 hr, catalyst amount was 0.5 wt% of the reaction system, and the mass ratio of o‐xylene/styrene was 7.5:1, a 100% conversion of styrene and 93.7% PXE yield was acquired. After four times recycle, the yield remains 53.3%. Comparing with the commercial liquid acid catalyst, it processing a higher catalytic property and recyclability. Moreover, this fresh dual acidic heterogeneous catalyst owning a promising future applied in other acidic catalytic reactions and provide a new method to modify catalyst.