Total Oxidation of Naphthalene Using Mesoporous CeO2 Catalysts Synthesized by Nanocasting from Two Dimensional SBA-15 and Three Dimensional KIT-6 and MCM-48 Silica Templates

Ceria catalysts have been prepared by a nanocasting procedure using SBA-15, MCM-48 and KIT-6 silica-based templates, and investigated for the total oxidation of naphthalene. In all cases cubic fluorite CeO₂ was prepared, and the structure of the template was replicated when SBA-15 and MCM-48 were used. The KIT-6 template was not replicated by the nanocasting synthesis, but in all cases mesoporous CeO2 was obtained with high surface areas (91–190 m² g^?1). All of the catalysts demonstrated high activity for naphthalene oxidation to CO₂, and the most active was the catalyst prepared from the KIT-6 template. The high activity was attributed to the small crystallite size of the CeO₂, combined with high surface area and the highly accessible catalyst surface.     

Synthesis and Characterization of Dendrimer-Templated Mesoporous Oxidation Catalysts

We report here the use of 4th and 5th generation dendrimers poly(propylene)imine (CU-D32 and CU-D64) as templating agents for the synthesis of mesoporous titanosilicate and vanadosilicate oxidation catalysts via solgel techniques. The physical properties of these mesoporous materials were characterized by TGA, BET, PXD and SEM/EDX analyses and these showed that the transition metals are evenly distributed throughout these silicates, which have interconnected spherical pores (approx. 12Å in diameter) and high surface areas of about 650m²g^–1. Kinetic studies showed that all transition metal-doped catalysts were highly selective at oxidizing cyclohexene to the corresponding epoxide. Additionally, CU-D64-templated catalysts were more catalytically active for cyclohexene epoxidation than CU-D32-templated catalysts as a result of differences in pore size. All CU-D64-templated catalysts exhibited epoxidation catalytic activity comparable to that of titanium doped MCM-41 materials.     

Preparation of MgO/MCM-22 catalysts by a novel two-step impregnation and their shape-selective performance in the synthesis of p-xylene

Shape-selective catalysts of MgO/MCM-22 were prepared by a novel two-step impregnation method and evaluated in the catalytic synthesis of p-xylene by alkylation of toluene with dimethyl carbonate. The two-step impregnation process combines the advantages of general impregnation and complexation impregnation for the preparation of metallic-oxide modified zeolite shape-selective catalysts. The coverage of the acidic sites on the external surface of the zeolite and the adjustment of the pore size of the zeolite can be achieved by two-step impregnation. Consequently, significant improvement in selectivity for p-xylene over the MgO/MCM-22 catalyst was realized.     

Preparation of sulfated alumina supported on mesoporous MCM-41 silica and its application in esterification

New types of mesoporous SA/MCM-41 solid acid catalysts were prepared by loading sulfated alumina (SA) on MCM-41. The prepared catalysts were characterized by XRD, IR, N₂ physisorption, elemental analysis, FT-IR of adsorbed pyridine and NH₃-TPD. The esterification of acetic acid with n-butanol and citric acid with n-butanol were used as model reactions to test the catalytic activities and reusability of the SA/MCM-41 solid acid catalysts. Compared with SA catalyst, SA/MCM-41 catalysts exhibited higher catalytic performances, which were attributed to their high BET surface area and large pore volume. Moreover, 20SA/MCM-41 solid acid catalyst showed excellent reusability in both esterifications.     

Functionalization of oxo-vanadium(IV) acetylacetonate over modified MCM-41: an efficient reusable catalyst for epoxidation reaction

A new hybrid heterogeneous catalytic system has been developed by post synthesis grafting method. 3-aminopropyltriethoxysilane (3-APTES) has been first anchored over mesoporous silica materials MCM-41. Upon reaction with oxo-vanadium(IV) acetylacetonate amine groups of 3-APTES afford vanadium(IV) active centers in the mesoporous matrix. The prepared hybrid material has been characterized by UV–vis, infrared (IR) spectroscopic analysis, small-angle X-ray diffraction and N₂ sorption studies and employed in epoxidation reactions as a catalyst. The catalyst showed excellent catalytic activity towards epoxidation reaction with various olefinic compounds using tert-BuOOH as oxidant under mild reaction condition. The effect of different solvents on epoxidation reaction has also been studied.     

Effect of pore size on the performance of mesoporous material supported chiral Mn(III) salen complex for the epoxidation of unfunctionalized olefins

A series of mesoporous MCM-41 and MCM-48 materials with different pore sizes were synthesized and used as supports to immobilize chiral Mn(III) salen complex. The heterogeneous catalysts were characterized by XRD, FT-IR, DR UV–vis, and N₂ sorption, and the results indicated the successful immobilization of chiral Mn(III) salen complex. The confinement effect of pore size on the catalytic performance of the heterogeneous catalysts was studied for the asymmetric epoxidation of unfunctionalized olefins with m-chloroperoxybenzoic acid as an oxidant. It was found that the conversions and enantiomeric excess (ee) values were closely correlated with the pore sizes of parent supports. The catalysts immobilized on the large-pore mesoporous supports exhibited higher conversions, and for the catalysts immobilized on MCM-41 materials, the ee values improved with increasing pore size. However, for the MCM-48 material-supported catalysts, the compatible pore size of the support with the substrate was beneficial for obtaining higher enantioselectivity in olefin epoxidation.     

Enantioselective epoxidations catalyzed by zeolite MCM-22 encapsulated Jacobsen's catalyst

A novel method for the encapsulation of homogeneous catalysts within the supercages (7.1×18.2 Å) of zeolite MCM-22 has been developed. By way of example, the well known asymmetric oxidation catalyst (R,R)-N,N-bis(3,5-di-tert-butylsalicylidedene)-1,2-cyclohexanediaminemanganese(III) chloride, a.k.a Jacobsen's catalyst, was occluded in MCM-22 during the zeolite synthesis. This ship-in-a-bottle complex exhibited both higher activity and enantioselectivity for the epoxidation of -methylstyrene compared with the homogeneous catalyst.     

Synthesis, characterization of high Ti-containing Ti-MCM-41 catalysts and their activity evaluation in oxidation of cyclohexene and epoxidation of higher olefins

A series of titanium rich isomorphous substituted Ti MCM-41 and HMS materials have been synthesized with different Si/Ti ratios. The highest amount of Ti incorporated in synthesis gel is in TiMCM-41 (Si/Ti = 10). Whereas for TiHMS catalysts, Ti is incorporated up to Si/Ti = 50 successfully without forming any extra framework TiO₂. Cyclohexene epoxidation reaction with dry tert-butyl hydroperoxide (TBHP) as an oxidant has been studied to evaluate the catalytic properties of Ti substituted mesoporous catalysts. The effect of molar ratio of substrate:oxidant in this reaction has been studied and high conversion, high selectivity were achieved at 2: 1 molar ratio with TiMCM-41 (Si/Ti =25). Dry TBHP (in dichloromethane) and chloroform were found as good oxidant and solvent system for this reaction. Pure siliceous mesoporous silica and low `Ti' substituted mesoporous silicas were found to be efficient catalysts for oxidation of cyclohexene. An interesting variation of the selectivity from allylic oxidation to epoxidation during oxidation of cyclohexene was observed with an increase in the Ti amount in the mesoporous framework. The allylic oxidation of cyclohexene has been carried out using molecular oxygen as an oxidant and in the presence of a small amount of TBHP as initiator. Siliceous HMS materials gave better conversion compared to MCM-41 type of materials and other conventional silicas like silica gel, fumed silica etc. in allylic oxidation of cyclohexene. Epoxidation of higher cyclic olefins like cyclooctene, cyclododecene, cis-cyclododecene and linear olefins 1-Heptene, cis-2-hexene, 1-undecene was carried out over TiMCM-41 (Si/Ti = 25). Ti substituted mesoporous catalysts were characterized by elemental analysis, XRD, FTIR, UVDRS, ²⁹SiMASNMR, BET surface area and pore size distribution techniques.     

Methanol synthesis over Pd/SiO2 with narrow Pd size distribution prepared by using MCM-41 as a support precursor

All silicious MCM-41 was investigated as a support or a support precursor for Pd/SiO₂ and prepared catalysts were tested for methanol synthesis from CO and H₂. The methods of Pd loading on the MCM-41 were impregnation, seed impregnation and chemical vapor deposition (CVD). For both impregnations, most Pd existed outside of the pore as large particles, and only a small part of Pd was inserted into the pore of MCM-41 retaining the initial structure. On the contrary, in the catalyst prepared by CVD method, the MCM-41 structure was completely destroyed to become amorphous SiO₂. Yet the average Pd particle size in this catalyst was smaller and its distribution was narrower than those of the catalysts prepared by impregnation methods. In the methanol synthesis from CO hydrogenation the catalyst prepared by CVD showed higher methanol selectivity than other MCM-41-derived catalysts. This result was considered to be due to the more uniform distribution of the Pd particle size.     

Skeletal Isomerization of n-Pentane over Platinum-Promoted Tungstophosphoric Acid Supported on MCM-41

Skeletal isomerization of n-pentane in the presence of hydrogen has been studied over Pt-promoted H₃PW₁₂O₄₀ (TPA)/MCM-41 bifunctional catalyst. A series of solid acid catalysts with different loading amount of TPA and Pt were prepared and characterized by XRD, FT-IR and XPS. The optimal catalytic activity of Pt-TPA/MCM-41 was observed with 2% Pt and 30% TPA. According to the cracked products distribution, this is typical of a monomolecular bifunctional metal-acid mechanism. Further, catalysts with different combination of noble metals (Pt, Pd and Ru), heteropoly acids (HPAs) (TPA, tungstosilicic acid (TSA), and molybdophosphoric acid (MPA)) and supports (MCM-41, SBA-1 and SiO₂) were also synthesized and their catalytic performances were compared.     

Bifunctional mesoporous Cu–Al–MCM-41 materials for the simultaneous catalytic abatement of NOx and VOCs

This study explored the possibility of using waste organic solvent as the source of volatile organic compound (VOC) and it served as a reducing agent of selective catalytic reduction (SCR) deNO_x process, in which the VOC itself can be catalytically oxidized on the mesoporous Cu and/or Al substituted MCM-41 catalysts. The synthesized Cu–Al–MCM-41 catalysts were extensively characterized by powder low-angle X-ray diffraction (XRD), N₂ adsorption–desorption measurements, transmission electron microscopy (TEM), UV–Visible diffuse reflectance spectroscopy (UV–Vis DRS), ²⁷Al magic angle spinning-nuclear magnetic resonance spectroscopy (MAS-NMR), electron paramagnetic resonance spectroscopy (EPR) and inductively coupled plasma–mass spectrometer (ICP–MS) analysis. The XRD, TEM and N₂ adsorption–desorption studies clearly demonstrated the presence of a well ordered long range hexagonal array with uniform mesostructures. The Cu–Al–MCM-41 materials showed a better long-term-stability than that of copper ion-exchanged H–ZSM-5 (Cu–ZSM-5) zeolite. The Cu–Al–MCM-41 material was found to be an efficient catalyst than that of Cu–MCM-41 without aluminum for the simultaneous catalytic abatement of NO_x and VOCs, which was attributed to the presence of well dispersed and isolated Cu²⁺ ions on the Cu–Al–MCM-41 catalyst as observed by UV–Vis DRS and EPR spectroscopic studies. And the presence of aluminum (Al³⁺ ions) within the framework of Cu–Al–MCM-41 stabilized the isolated Cu²⁺ ions thus it led to higher and stabilized activity in terms of NO_x reduction.     

MCM-41 supported CuO/Bi2O3 nanoparticles as potential catalyst for 1,4-butynediol synthesis

CuO/Bi₂O₃ (CuO/Bi₂O₃/MCM-41) nanoparticles supported on MCM-41 were synthesized by a facile impregnation method. The products were characterized by nitrogen adsorption/desorption, X-ray diffraction (XRD), H₂ temperature programmed reduction (H₂-TPR) and scanning electron microscopy (SEM). XRD patterns indicated the presence of crystalline CuO and Bi₂O₃ phase for CuO/Bi₂O₃/MCM-41 catalyst. TPR results revealed CuO nanoparticles were dispersed well on MCM-41. SEM results showed that the nanoparticles were located on the MCM-41. The activity of the catalysts towards ethynylation of formaldehyde for 1,4-butynediol synthesis was evaluated at atmospheric pressure. Compared with unsupported CuO/Bi₂O₃ and commercial Cu/Bi-based catalyst, CuO/Bi₂O₃/MCM-41 catalyst showed maximum conversion (51%) and selectivity (94%) towards 1,4-butynediol. The results show that CuO/Bi₂O₃ catalysts supported on MCM-41 have potential for 1,4-butynediol synthesis in industrial application.     

Preparation of Titanium-Containing Carbon–Silica Composite Catalysts and Their Liquid-Phase Epoxidation Activity

Titanium-containing catalysts have been prepared by two different post-synthesis methods using activated carbon and carbon-silica composite as catalyst supports. They have been applied to the liquid-phase epoxidation of cyclohexene with tert-butyl hydroperoxide (TBHP) and H₂O₂. The carbon-silica composite catalyst showed a high conversion and selectivity to epoxide compared to the Ti-carbon catalyst and silica-based catalysts for the cyclohexene epoxidation with H₂O₂. The highest values of cyclohexene conversion and epoxide selectivity were obtained with the carbon-silica composite catalyst having a titanium content of 3 wt%.     

基于MCM-41的镍基甲烷化催化剂活性与稳定性

采用浸渍法分别以MCM-41,Al₂O₃和SiO₂ 为载体制备了不同镍负载量的甲烷化催化剂,并在连续流动固定床反应装置上对其甲烷化催化活性进行了评价。研究结果表明,与Ni/Al₂O₃和Ni/SiO₂相比,相同镍负载量的Ni/MCM-41催化剂具有更好的催化活性。同时研究了Ni含量对于Ni/MCM-41催化剂催化活性的影响,发现随着Ni含量的增加,CO转化率和CH₄收率逐渐升高,并且在Ni含量大于10%（质量分数）以后趋于稳定。在n（H₂）：n（CO）=3：1、反应压力1.5 MPa、反应温度350℃及质量空速12000 ml·h^-1·g^-1的反应条件下,10%Ni/MCM-41催化剂CH₄选择性达到94.9%,CO转化率接近100%。在100 h催化活性稳定性试验中,10%Ni/MCM-41催化活性无明显下降,表现出良好的催化活性稳定性。采用X射线衍射（XRD）、氮气物理吸附（BET）、热重分析（TG）及氢气程序升温还原（H₂-TPR）等技术手段对催化剂进行了表征,结果表明Ni颗粒大小是影响Ni/MCM-41催化剂催化活性的主要因素。     

Heterogeneously Catalysed Aldol Reactions in Supercritical Carbon Dioxide as Innovative and Non-Flammable Reaction Medium

Aldol reactions of several aldehydes have been investigated over acidic and basic catalysts in supercritical carbon dioxide at 180 bar and 100 °C. Both acidic (Amberlyst-15, tungstosilicic acid (TSA) on SiO₂ and MCM-41) and basic (hydrotalcite) materials showed interesting performance in this preliminary study under the entitled reaction conditions. Small and linear aldehydes, such as propanal, butanal, pentanal and hexanal, react more efficiently than the branched 3-methylbutanal, which is converted much slower. Whereas Amberlyst-15 showed the highest conversion based on the catalyst mass, tungstosilicic acid-based catalysts were significantly better if the rates were related to the number of acidic sites (>1000 h^?1). The rate depends both on the dispersion and the kind of support. Strikingly, tungstosilicic acid (TSA) on MCM-41 was also an effective catalysts for the selective C=C double bond hydrogenation of 2-butenal and is therefore a potential catalyst for the ??one-pot?? synthesis of 2-ethyl-2-hexenal and 2-ethylhexanal via combined hydrogenation and aldol reaction from 2-butenal. A number of characterisation techniques, such as temperature-programmed desorption of ammonia (NH₃-TPD), transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS), etc. were used to get an insight into the catalyst structure, which support a high dispersion and strong acidity of the tungsten based species on silica and MCM-41.     

Enhanced ketalization activity of cyclohexanone and ethanediol over immobilized ionic liquid in mesoporous materials

Three different mesoporous molecular sieves, including MCM-41, MCM-48, and SBA-15, were synthesized by hydrothermal process and characterized by XRD, BET and TEM. The chlorine-aluminate acidic ionic liquid of 1-butyl-3-methylimidazolium chloride-aluminum chloride ([Bmim]Cl-AlCl₃, denoted as Al-ILs) was prepared by two-step method. The immobilized ionic liquid (SBA-15/Al-ILs, MCM-41/Al-ILs, MCM-48/Al-ILs) was prepared through impregnating Al-ILs. The structures of composite catalysts were characterized by XRD, BET, FT-IR, TEM and XPS. The amounts of aluminum present in the resulting composite catalysts were detected by ICP-AES to calculate the amount of AL-ILs impregnated. The ketalization between cyclohexanone and ethanediol was used as the model reaction to test the catalytic activities of the composite catalysts. The effects of molar ratio of the reactants, reaction time, the catalyst dose, as well as the addition of cyclohexane were discussed in detail. Also, catalytic activities of three catalysts with different pore sizes were compared. Under comparable conditions, the SBA-15/Al-ILs composite catalyst exhibited much high catalytic activity and gave a maximum yield that was ca. 85.1%.     

Preparation of silica-immobilized titanium-containing silsesquioxane catalysts and activity for the epoxidation of alkenes

Silsesquioxanes containing tetrapodal titanium species and alkenylsilyl groups were immobilized onto dimethylsilyl-functionalized silica having mesopores by chemical tethering via hydrosilylative reaction in the presence of a Pt catalyst. The immobilized catalysts showed higher activity than their corresponding homogeneous catalyst towards the epoxidation of cyclooctene by tert-butylhydroperoxide, probably because of the improvement of the micro-environment around the titanium center. The reaction was found to be truly heterogeneous, since no further reaction proceeded after the separation of the catalyst by filtration. These catalysts also showed excellent catalytic activity for the epoxidation using hydrogen peroxide as an oxidant, while the parent homogeneous catalysts did not show any activity at all.     

AlCl3-promoted MCM-41-supported platinum catalysts with high activity and sulfur-tolerance for tetralin hydrogenation: Effect of Pt–Al interaction

AlCl₃-promoted MCM-41-supported platinum catalysts with different Al–Pt interaction sequences were prepared for tetralin hydrogenation under sulfur-containing condition. Platinum dispersion and acidity of the catalysts were improved by the introduction of aluminum. The aluminum-containing catalysts have similar acidity. Al–Pt interaction leads to the formation of electron-deficient platinum (Pt^δ +). A great improvement in sulfur-tolerance was observed on the catalyst that aluminum is grafted after the supporting of platinum.     

Characteristics of the Photocatalytic Oxidation of Methane into Methanol on V-Containing MCM-41 Catalysts

V-containing MCM-41 catalysts were prepared by a direct synthesis method under acidic and basic conditions and impregnation. Their photocatalytic reactivity was evaluated for the selective photocatalytic oxidation of methane with NO under UV irradiation at 295 K. Selective methanol formation was observed on V-MCM-41 prepared in acidic solution and imp-V/MCM-41, while only coupling reaction products were obtained on V-MCM-41 prepared in basic solution. The photocatalytic reactivity of the catalysts for the partial oxidation of methane was found to strongly depend on the local structure of the V-oxide species including the coordination and loading sites, i.e., the charge transfer excited states of the isolated tetrahedral V⁵⁺-oxide species supported on the catalyst surface act as the active sites for the selective photocatalytic oxidation of methane into methanol.     

Ti-containing MCM-41 catalysts for liquid phase oxidation of cyclohexene with aqueous H2O2 and tert-butyl hydroperoxide

Framework Ti-substituted and Ti-grafted MCM-41 mesoporous material has been prepared by direct hydrothermal synthesis and a post-synthesis grafting method. The materials have been tested as catalysts for cyclohexene oxidation with aqueous H₂O₂ and tert-butyl hydroperoxide (TBHP). With aqueous H₂O₂ in methanol, the major products were cyclohexene diol and its methyl ethers. No cyclohexene oxide was produced. Titanium leaching was a serious problem, and the catalyst lost its activity irreversibly after only one cycle of reaction. With TBHP, the selectivity for cyclohexene oxide was near 100%, titanium leaching was negligible, and the catalyst could be repeatedly used after regeneration without suffering significant activity loss. However, the reaction rate was lower than when H₂O₂ was used. Framework substituted material and catalysts prepared by Ti-grafting onto a MCM-41 support behaved similar, but the Ti-grafted MCM-41 is somewhat more active. The turnover frequency (TOF) per mole of Ti decreases with an increase of Ti content in the catalyst. This is caused by a reduced Ti dispersion within the silica matrix. This revised version was published online in July 2006 with corrections to the Cover Date.