Highly selective synthesis of styrene oxide over phosphotungstic acid supported on mesoporous Mn-MCM-41 molecular sieves

Tungstophosphoric acid (H₃PW₁₂O₄₀) (PW) catalysts supported on mesoporous Mn-MCM-41(n _Si/n _Mn = 25) with various (10, 20 and 30 wt%) acid loadings were prepared by impregnation, and their physical chemical properties were characterized by powder X-ray diffraction (XRD), N₂ adsorption–desorption, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), high resolution transmission electron microscopy (HRTEM), and X-Ray Photoelectron Spectroscopy (XPS). The host material suffers severe structural distortions at higher loading, which lead to a considerable loss of long-range orders. Their catalytic performances were evaluated in the epoxidation of styrene with dilute H₂O₂ (30%) as an oxidizing agent under liquid phase reaction conditions over PW/Mn-MCM-41 catalysts for selective synthesis of styrene oxide. The influences of various reaction parameters such as temperature, time, solvents, PW loading and catalyst amount, styrene to H₂O₂ mmol ratios and acetonitrile (MeCN) to N,N-dimethylformamide (DMF) volume ratios on the conversion of styrene and yield as well as selectivity of styrene oxide have also been studied in details. The results revealed that 20% PW/Mn-MCM-41 (n _Si/n _Mn = 25) was more active than other catalysts. The PW/Mn-MCM-41, moreover, was found to be reusable and environmentally benign for the epoxidation of styrene.     

Immobilization of the heteropoly acid (HPA) H4SiW12O40 (SiW12) on mesoporous molecular sieves (HMS and MCM-41) and their catalytic behavior

Supported catalysts, consisting of SiW₁₂ immobilized on hexagonal mesoporous silica (HMS) and its aluminum-substituted derivative (MCM-41) with different loadings and calcination temperatures, have been prepared and characterized by X-ray diffraction, FT-IR and NH₃-temperature programmed desorption. It is shown that SiW₁₂ retains the Keggin structure on the mesoporous molecular sieves and no HPA crystal phase is developed, even at SiW₁₂ loadings as high as 50 wt%. In the esterification of acetic acid byn-butanol, supported catalysts exhibit a higher catalytic activity and stability and held some promise of practical application. In addition, experimental results indicate that the loaded amount of SiW₁₂ and the calcination temperatures have a significant influence on the catalytic activity, and the existence of aluminum has also an effect on the properties of supported catalysts.     

Nontemplate sol–gel synthesis of catalytically active mesoporous titanosilicates

A method for the nontemplate sol–gel synthesis of micro-mesoporous and mesoporous titanosilicates is developed using commercially available raw materials (a mixture of oligomer esters of orthosilicic acid (Ethylsilicate-40) and a water–alcohol solution of titanium(IV) ethoxide). The effect of the pH values of the reaction mixture on sol–gel synthesis is studied using the characteristics of the porous structure of titanosilicates. Samples of amorphous structure with different textural characteristics are obtained by varying the pH in the range of 3–10: specific surface area, 320–740 m²/g; micropore volume, 0.04–0.15 cm³/g; and mesopore volume, 0–0.92 cm³/g. It is shown that a sample of mesoporous titanosilicate obtained with alternating pH values has maximum catalytic activity in the oxidation reaction of 4-tert-butylphenol (TBP) in aqueous solutions of hydrogen peroxide. (Conversion of 4-tert-butylphenol, 45 wt %; selectivity of the formation of 4-tert-butylcatechol, 66 wt %. Conditions: 10 wt % of titanosilicate; TBP/H₂O₂ = 1/2; 75°C; 1 h).     

High permeability nano-composite membranes based on mesoporous MCM-41 nanoparticles in a polysulfone matrix

Mixed matrix membranes containing mesoporous MCM-41 nanoparticles with 80 nm particle size have been prepared. These smaller nanoparticles lead to a high polymer/particle interfacial area and provide an opportunity to fabricate composites containing up to 40 wt% of molecular sieve in the polymer matrix. With 40 wt% of nano-sized MCM-41 silica, gas permeability of the mixed matrix membranes is shown to increase by up to 300% when compared to the neat polymer. In addition, amine-functionalization of MCM-41 can significantly enhance CO₂/CH₄ selectivity of the mixed matrix membranes.     

Dispersion measurement of heteropoly acid supported on KIT-1 mesoporous material

Heteropoly acid (HPA) catalysts supported on KIT-1 mesoporous material were prepared with different loadings and characterized using XRD, UV–VIS and N₂ adsorption. Supported HPA was dispersed mainly on the inner surface of pores, resulting in the disappearance of XRD peaks. The diffraction peaks of HPA from the KIT-1 mesoporous material loaded with HPA of 41 wt% was very weak compared to those of physical mixtures of HPA and mesoporous material. The remaining adsorption amount of 1-butene on the supported HPA catalysts revealed the exposed amount of HPA molecules, which is useful in determining the HPA dispersion. HPA dispersion of supported HPA catalysts was useful to interpret their catalytic activity in the skeletal isomerization of 1-butene.     

Catalytic Behavior of Alumina-Promoted Sulfated Zirconia Supported on Mesoporous Silica in Butane Isomerization

Alumina-promoted sulfated zirconia was supported on mesoporous molecular sieves of pure-silica MCM-41 and SBA-15. The catalysts were prepared by direct impregnation of metal sulfate onto the as-synthesized MCM-41 and SBA-15 materials, followed by solid state dispersion and thermal decomposition. Measurements of XRD and nitrogen adsorption isotherms showed that the structures of resultant materials retain well-ordered pores, even with ZrO₂ loading as high as 50 wt%. The characterization results indicated that most of the promoted sulfated zirconia were well dispersed on the internal surface of the ordered mesopores. The catalytic behavior of the alumina-promoted sulfated zirconia supported on mesoporous silica was studied in n-butane isomerization. The supports of mesoporous structures led to high dispersion of sulfated zirconia in the meta-stable tetragonal phase, which was the catalytic active phase. The high performance of alumina-promoted catalysts was ascribed to the sulfur retention by alumina.     

H3PW12O40 Supported on AlMCM-41 molecular sieves: An effectual catalyst for t-butylation of anisole

Mesoporous AlMCM-41 (Si/Al = 25) molecular sieves was synthesized and impregnated with different loadings (10, 20 and 30 wt% H₃PW₁₂O₄₀) of phosphotungstic acid. Their catalytic performance was examined in the vapour phase alkylation of anisole with tert-butanol. The major products were found to be 2-tert-butyl anisole (2-TBA), 4-tert-butyl anisole (4-TBA), 2,4-di-tert-butyl anisole (2,4-DTBA). 4-TBA was the major product formed with high selectivity. The influence of temperature, feed ratio, WHSV was studied and the results are discussed.     

PW/MCM-41催化剂的合成及对合成柠檬酸三丁酯反应的研究

制备了负载H₃PW₁₂O₄₀(PW)杂多酸的PW/MCM-41催化剂,用XRD和BET等方法表征了催化剂的结构。在负载质量分数达40%的催化剂上,XRD未检测到PW杂多酸的晶相峰。考察了不同负载质量分数的 PW/MCM-41催化剂对反应的影响。重点讨论了催化剂的活化温度、酸醇摩尔比和反应温度等因素对酯化反应的影响。最佳操作条件：PW/MCM-41负载杂多酸催化剂的磷钨酸最佳负载质量分数 40%,催化剂焙烧温度300 ℃,酸醇摩尔比1∶4,反应温度140 ℃,反应时间6～7 h。实验结果表明,负载质量分数为40%的PW/MCM-41催化剂是替代硫酸合成柠檬酸三丁酯的理想催化剂,且稳定性良好。     

Reactions of turpentine using Zr-MCM-41 family mesoporous molecular sieves

The mesoporous molecular sieve Zr-MCM-41 was synthesized under hydrothermal conditions. Zr-MCM-41 material was impregnated using sulfuric acid to prepare SO ₄^2-/Zr-MCM-41. The obtained materials were characterized by XRD, FT-1R, N₂ adsorption/desorption and NH₃-TPD analysis technique. The results indicated that SO ₄^2-/Zr-MCM-41 was of better mesoporous structure, long range ordering and crystallites, and that SO ₄^2-existed in the skeleton of Zr-MCM-41 and enhanced its acidity. SO₄^2-/Zr-MCM-41 were firstly used as catalyst in the esterification of terpineol. The catalytic results were compared with those obtained by using sulfuric acid (33%), HY, HZSM-5 and SO₄^2-/ZrO₂ as catalysts. It was showed that SO₄^2-/Zr-MCM-41 were not only of better catalytic activity and selectivity, but also of better regenerable performance. The effects of synthesis methods of catalysts and Si/Zr mole ratio on catalytic properties were also studied. In addition, AlCl₃ was supported on the synthesized mesoporous molecular sieves to get composite catalysts that were firstly used to catalyze the polymerization of -pinene. It was showed that the catalytic result of the composite catalyst was better than that AlCl₃ alone.*To whom correspondence should be addressed. E-mail: yushitao@elong.com     

Kinetic studies on the condensation reaction of 2-methylol-4-t-butylphenol with 4-t-butylphenol using acid catalysts. I

The rates of the individual reactions of 2-methylol-4-t-butylphenol with 4-t-butylphenol were measured under varying mole ratios of reactants in the presence of different acid catalysts (5.0 × 10^?3 N to 2.0 × 10^?4 N) at five different temperatures (60, 65, 70, 75, and 80°C). In all the experiments, the reactions were found to obey second-order rate law. The values of the Arrhenius parameters and the entropy of activation for the overall reaction were calculated. The relative catalytic efficiencies of the acid catalysts followed the order HNO₃ > HCl > H₂SO₄.     

Preparation of nanosize Pt clusters using ion exchange of Pt(NH3) 4 2+ inside mesoporous channel of MCM-41

Mesoporous molecular sieve MCM-41 with a Si/Al ratio of 35 was obtained by hydrothermal synthesis using a gel mixture with a molar composition of 6 SiO₂0.1 Al₂O₃1 hexadecyltrimethylammonium chloride 0.25 dodecyltrimethylammonium bromide 0.25 tetrapropylammonium bromide0.15 (NH₄)₂O1.5 Na₂O300 H₂O. The MCM-41 sample was calcined in O₂ flow at 813 K and subsequently ion exchanged with Ca²⁺. A small Pt cluster has been supported on the MCM-41 sample following a procedure using ion exchange of Pt(NH₃) ₄ ²⁺ . The Pt(NH₃) ₄ ²⁺ ion supported on MCM-41 has been activated in O₂ flow at 593 K and subsequently reduced with Fh flow at 573 K, in the same way used for the preparation of a Pt cluster entrapped inside the supercage of zeolite NaY. The resulting Pt cluster supported on the MCM-41 shows hydrogen chemisorption oftotal two H atoms per Pt at 296 K (based on the total amount of Pt) and high catalytic activity for hydrogenolysis of ethane. The chemical shift in¹²⁹Xe NMR spectroscopy of adsorbed xenon indicates that the Pt cluster is located inside the mesoporous molecular sieve.     

Advances in the study of nano-structured Co/MCM-41 materials: surface and magnetic characterization

Co-modified mesoporous supports with MCM-41 structure and several metal loadings were successfully synthesized by a fast wet impregnation method. The nature and location of different Co species formed on the solids were inferred by TEM/SEM, XPS, XANES/EXAFS, adsorption of pyridine coupled to FT-IR spectroscopy and temperature dependence of magnetization. The presence of Co oxide species (clusters and Co₃O₄ nanoparticles) inside the channels of all the samples could be evidenced by TEM, XPS and XANES/EXAFS. In this sense, the surface Co/Si atomic ratios obtained by XPS were notably lower than the corresponding bulk Co/Si ratios obtained by ICP, indicating that the Co atoms are mostly incorporated inside the mesopores channels of the silica matrix. Nevertheless, by TEM, Co₃O₄ nanoparticles of small size segregated on the external surface of the silicate were also observed for the higher metal loadings. The temperature dependence of the magnetization performed for the Co/M(2.5) sample allowed to assign its superparamagnetic behavior to the presence of clusters and Co₃O₄ nanoparticles of very small size that grow inside the MCM-41 mesopores. Therefore, the analyses presented in this work indicate that a Co theoretical loading of 2.5 wt% leads to the formation of Co oxide nanospecies in the MCM-41 support with a particular superparamagnetic behavior. This sample with improved structural and magnetic properties result an attractive porous solid for drug hosting, to be applied in the field of the controlled release of medicaments.     

Development of mesoporous Al,B-MCM-41 materials: Effect of reaction temperature on the catalytic performance of Al,B-MCM-41 materials for the cyclohexanone oxime rearrangement

A series of aluminum–boron–silicate MCM-41 mesoporous materials and their counterparts treated with NH₄F aqueous solution were synthesized and characterized by using XRD, MAS NMR, nitrogen physisorption, DRIFT, TG-DTA, TP/MS and pyridine adsorption. All of the samples showed typical MCM-41 structural and textural properties. ²⁷Al MAS NMR showed that the aluminum environment was mainly four-coordinated and six-coordinated aluminum for non-fluorinated samples and fluorinated ones, respectively. Boron was in the trigonal framework environment at ca. catalytic reaction temperatures and the NH₄F treatment did not affect the boron environment in our Al,B-MCM-41 materials. All of the Al,B-MCM-41 materials studied contained both Brønsted and Lewis acid sites. However, the strong acid Brønsted/Lewis ratios decreased in the fluorinated catalysts. Moreover, the influence of temperature was studied on the cyclohexanone oxime conversion and the product selectivity in the 623–798 K range. Results indicated that temperatures lower than 748 K favored Beckmann rearrangement to -caprolactam, whereas, at higher temperatures the main reaction was cyclohexanone oxime hydrolysis to cyclohexanone. The aluminum–boron–silicate MCM-41 mesoporous materials treated with NH₄F improved both the selectivity to -caprolactam (related mainly to boron content) and their life span (related to their lower ratios of strong Brønsted/Lewis acid sites).     

Synthesis of mesoporous molecular sieves: influence of aluminum source on Al incorporation in MCM-41

Three series of mesoporous aluminosilicate molecular sieves, MCM-41, with various Si/Al ratios were synthesized using different aluminum sources (aluminum isopropoxide, pseudo boehmite and aluminum sulfate). XRD analysis, temperature programmed desorption ofn-butylamine,²⁷Al and²⁹Si MAS NMR, and catalytic alkylation test indicated that aluminum isopropoxide is a better source for incorporating aluminum in the framework of MCM-41 type molecular sieves with better crystallinity and acid characteristics.     

High loading of C60 in nanochannels of mesoporous MCM-41 materials

Very high loadings of C₆₀ and C₆₀⁻ anions in MCM-41 mesoporous materials have been achieved by modifying the channel surface with amino-functional group. Detailed physical properties of these mesoporous materials containing C₆₀ were characterized by EPR, NMR, XRD, FTIR and UV–vis spectroscopic techniques. The surface area and pore size of mesoporous materials were further determined by N₂ adsorption–desorption isotherms. The mesopores of MCM-41 show sieving behavior in excluding the larger sized C₁₂₀O while absorbing the smaller C₆₀ as indicated in the EPR studies.     

Atom Transfer Radical Polymerisation with an Immobilised [RuCl2(p-cymene)]2 Dimer

[RuCl₂(p-cymene)]₂ has been immobilized on silica and mesoporous MCM-41 and used as a catalyst for the atom transfer radical polymerisation (ATRP) of styrene, (methyl)methacrylate and acrylonitrile. The heterogeneous catalyst has a comparable activity as the homogeneous analogues and showed no significant loss of catalytic activity when reused.     

Tertiary butylation of phenol over mesoporous H–FeMCM-41

Trivalent-iron-substituted mesoporous molecular sieve catalysts (FeMCM-41) were synthesized hydrothermally and characterized systematically by various analytical and spectroscopic techniques. Temperature-programmed desorption studies of ammonia of the protonated catalyst (H–FeMCM-41) indicate a broad distribution of the acid sites. Vapour-phase alkylation of phenol with t-butyl alcohol (2-methyl-2-propanol) was carried out over this solid acid catalyst and p-t-butyl phenol was obtained as the major product with high selectivity.     

Catalytic study of MCM-41 immobilized RhCl3 for the hydroformylation of styrene

RhCl₃ was chemically immobilized on mesoporous silicate MCM-41 functionalized by amine or phosphorus organosilane to form heterogeneous catalysts: RhCl₃/MCM-41(NH₂) and RhCl₃/MCM-41(PPh₂). XRD and N₂ adsorption–desorption studies illustrated that the functionalized MCM-41 maintained the mesoporous structural ordering, but exhibited reduced pore sizes, total pore volumes and BET surface areas. XPS characterization indicated that chemical interaction between rhodium species of RhCl₃ and the surface ligands occurred, and rhodium (III) species were reduced to lower oxidation states. RhCl₃/MCM-41(NH₂) was tested to be stable for recycling, however a significant rhodium leakage was observed for RhCl₃/MCM-41(PPh₂). The catalytic system formed of the prepared RhCl₃/MCM-41(NH₂) catalyst and additional PPh₃ (PPh₃/Rh = 2.5) showed very good catalytic activity and high selectivity toward the branched aldehydes in the hydroformylation of styrene.     

Synthesis and Characterization of Mesoporous Silica Functionalized with Calix[]arene Derivatives

This work reports a new method to covalently attach calix[4]arene derivatives onto MCM-41, using a diisocyanate as a linker. The modified mesoporous silicates were characterized by fourier transform infrared spectroscopy (FTIR), thermal analysis (TGA) and elemental analysis. The FTIR spectra and TGA analysis verified that the calix[4]arene derivates are covalently attached to the mesoporous silica. The preservation of the MCM-41 channel system was checked by X-ray diffraction and nitrogen adsorption analysis.     

Pd(0)-<Emphasis Type="Italic">S</Emphasis>-methylisothiourea grafted onto mesoporous MCM-41 and its application as heterogeneous and reusable nanocatalyst for the Suzuki,Stille and Heck cross coupling reactions

In this project palladium (0) S-methylisothiourea was grafted into MCM-41 mesoporous silica. Palladium (0) S-methylisothiourea complex supported on MCM-41 (Pd(0)-SMT-MCM-41), as heterogeneous and reusable catalyst, was used in C–C bond formation between various aryl halides with sodium tetraphenylborate or phenylboronic acid (Suzuki reaction), aryl halides with triphenyltin chloride (Stille reaction), and aryl halides with styrene or n-butyl acrylate (Heck reaction). This catalyst was characterized by various physico-chemical techniques such as X-ray diffraction, transmission electron microscopy, scanning electron microscopy (SEM/EDX), thermal gravimetric analysis (TGA/DTA), fourier transform infrared spectroscopy and inductively coupled plasma. The results indicated that Pd(0)-SMT-MCM-41 catalyst could be easily recovered from reaction mixture for several consequence runs without significant loss of its catalytic activities.