H2SO4和Al2（SO4）3改性中孔分子筛Al-MCM-41及其催化性能

用SO24-物质的量相同的H2SO4和Al2(SO4)3分别对Al-MCM-41进行改性,得到样品SO42-/Al-MCM-41和Al/SO24-/Al-MCM-41。采用X射线多晶衍射(XRD)、红外光谱(FTIR)、N2吸附-脱附和NH3程序升温脱附(NH3-TPD)等测试技术对样品进行表征。分别用H2SO4、MCM-41、Al-MCM-41、SO42-/Al-MCM-41和Al/SO24-/Al-MCM-41催化合成丙酸香叶酯,比较了它们的催化性能。结果表明,H2SO4和Al2(SO4)3改性对Al-MCM-41中孔分子筛结构影响不明显,都可提高其酸性,改性后中孔分子筛的骨架仍保持着六方介孔结构,孔径、孔容和比表面积有所降低,但用Al2(SO4)3改性的分子筛酸性和催化性能更强;SO42-/Al-MCM-41的酸催化活性主要源于SO42-与分子筛表面硅羟基作用形成的双齿螯合配位结构,而Al/SO42-/Al-MCM-41的酸催化活性一方面来自SO24-与分子筛表面硅羟基作用形成的双齿螯合配位结构,另一方面,也来自与分子筛骨架接枝的铝,使其产生了更多的Brnsted酸中心。     

Evaluation of various types of Al-MCM-41 materials as catalysts in biomass pyrolysis for the production of bio-fuels and chemicals

MCM-41, is one of the latest members of the mesoporous family of materials. They possess a hexagonal array of uniform mesopores (1.4–10 nm), high surface areas (>1000 m²/g) and moderate acidity. Due to these properties the MCM-41 materials are currently under study in a variety of processes as catalysts or catalyst supports. The objective of this study was to evaluate different types of MCM-41 materials as potential catalysts in the catalytic biomass pyrolysis process. We expected that the very high pore size and the mild acidity of these materials could be beneficial to reformulate the high molecular weight primary molecules from biomass pyrolysis producing useful chemical (and especially phenolic compounds) and lighter bio-oil with less heavy molecules. Three different samples of Al-MCM-41 materials (with different Si/Al ratio) and three metal containing mesoporous samples (Cu–Al-MCM-41, Fe–Al-MCM-41 and Zn–Al-MCM-41) have been synthesised, characterized and tested as catalysts in the biomass catalytic pyrolysis process using a fixed bed pyrolysis combined with a fixed catalytic reactor and two different types of biomass feeds. Compared to conventional (non-catalytic) pyrolysis, it was found that the presence of the MCM-41 material alters significantly the quality of the pyrolysis products. All catalysts were found to increase the amount of phenolic compounds, which are very important in the chemical (adhesives) industry. A low Si/Al ratio was found to have a positive effect on product yields and composition. Fe–Al-MCM-41 and Cu–Al-MCM-41 are the best metal-containing catalysts in terms of phenols production. The presence of the Al-MCM-41 material was also found to decrease the fraction of undesirable oxygenated compounds in the bio-oil produced, which is an indication that the bio-oil produced is more stable.     

Photophysical properties of a naphthalimide derivative encapsulated within Si-MCM-41, Ce-MCM-41 and Al-MCM-41

4-Piperazinyl-N-methyl-1,8-naphthalimide (PMN) was synthesized and encapsulated into mesoporous molecular sieves. The fluorescent emission spectra and fluorescence decay of PMN/M-MCM-41 (where M = Si, Ce, Al) were used to investigate the photophysical properties of the hybrid composites. The emission intensity of 4-piperazinyl-N-methyl-1,8-naphthalimide can be increased by decreasing the pH environment of the hybrid composites; the emission intensity varied with different MCM-41 hosts in the order: PMN/Al-MCM-41 > PMN/Si-MCM-41 > PMN/Ce-MCM-41; the fluorescence lifetime of PMN molecules followed the same order. The reasons for the improved fluorescence intensity and the prolonged lifetime of PMN in a low pH environment and Al-MCM-41 are discussed.     

Synthesis, characterization, and catalytic properties of a hydrothermally stable Beta/MCM-41 composite from well-crystallized zeolite Beta

A Beta/MCM-41 composite has been synthesized with a new method by using well-crystallized zeolite Beta as silica and aluminum source. The prepared composite was characterized by XRD, FTIR, N₂ adsorption/desorption at 77 K, FE-SEM, DTG, ²⁹Si MAS NMR spectral techniques. It was shown that the composite consisted of a highly ordered mesoporous MCM-41 phase and a zeolite Beta phase. Its hexagonal mesoporous structure was still retained after statically treated for 120 h in boiling water. In contrast, the structure of generally synthesized Al-MCM-41 nearly completely collapsed. This might be attributed to the assembly of the dissolved fragments such as the first and/or secondary structural units of zeolite Beta into the mesoporous structure around surfactant micelles. This is supported by the catalytic result that the prepared composite showed higher activity and selectivity for medium fraction in hydrocracking of Daqing vacuum residue than the parent zeolite Beta, the Al-MCM-41 as well as the mechanical mixture of these two materials.     

Immobilization of Ru(II)(salen)(PPh3)2 on Mesoporous MCM-41/SBA-15: Characterization and Catalytic Applications

Ru(II)(salen)(PPh₃)₂ immobilized on MCM-41 and SBA-15 modified with aminopropyl groups as linkers has been synthesized and characterized by elemental analysis, TEM, FTIR, BET, and TGA. Elemental analysis shows that the grafted samples contain 0.7–0.8 wt.% Ru. The retaining of long range ordering of the mesoporous MCM-41 and SBA-15 supporting materials after grafting is evident from TEM and N₂ adsorption/desorption measurements. FTIR and TGA spectra show the formation of metal salen complexes with the amino groups acting as connectors to the SiO₂ surface. Both grafted materials were successfully applied as catalysts for the olefination of various aldehydes with very good yields and high E-selectivity. The catalyst materials are recyclable for several catalytic runs.     

Alkylation of Phenol with tert-Butanol Catalyzed by Mesoporous Material with Enhanced Acidity Synthesized from Zeolite MCM-22

Using zeolite MCM-22 as source and cetyltrimethylammonium bromide (CTAB) as template, mesoporous material denoted as M-MCM-22 with enhanced acidity has been synthesized and characterized by XPD, FT-IR, N₂ adsorption–desorption, ²⁷Al-MAS NMR, IR spectra of pyridine adsorption, and NH₃-TPD techniques, etc. The catalytic performance of M-MCM-22 was tested in alkylation of phenol with tert-butanol, indicating that M-MCM-22 showed highly and steadily catalytic properties. The highest conversion of phenol could be achieved at 418 K, while the highest selectivity to 2, 4-di-TBP was obtained at 398 K. It is found that high temperature is advantageous to form 4-TBP, whereas low weight hourly space velocity (WHSV/h^?1) is helpful for both conversion of phenol and selectivity to 2,4-DTBP. It is also shown that high ratio of tert-butanol/phenol is beneficial for obtaining high conversion of phenol and selectivity to 2,4-di-TBP.     

On the Confinement Effect During Catalytic Reaction Over Al-MCM-41

A comprehensive study has been made on the cracking abilities of mesoporous aluminosillicate MCM-41 materials with different Si/Al ratios (15–∞) and pore diameters (1.6–3.0 nm) by using 1,3,5-triisopropylbenzene (1,3,5-TiPB) cracking as the test reaction. The roles of Al content and pore diameter on the catalytic features of the samples were evaluated by the conversion of 1,3,5-TiPB, coke content and deactivation parameters. It is found that the catalytic activity is mainly controlled by adsorptive properties towards the reactant and the dispersion of acid sites. In terms of their catalytic performances, cracking reaction over aluminosilicate mesoporous materials is more favorable for catalysts with smaller pore size and higher Al concentration. Moreover, coking is found responsible for catalyst deactivation during 1,3,5-TiPB cracking reaction over Al-MCM-41.     

Efficient catalysis of mesoporous Al-MCM-41 for Mukaiyama aldol reactions

Mesoporous aluminosilicates, Al-MCM-41 (Si/Al = 20 and 50), efficiently catalyzed Mukaiyama aldol reaction of benzaldehyde with 1-(trimethylsiloxy)cyclohexene in CH₂Cl₂ at 0 °C to afford the corresponding β-trimethylsiloxy ketone in quantitative yield. On the other hand, mesoporous silica (MCM-41), amorphous SiO₂–Al₂O₃, and H–Y and H-ZSM-5 zeolites barely catalyzed the reaction. Additionally, the less ordered Al-MCM-41 prepared by mechanical compression exhibited much lower catalytic activity compared with Al-MCM-41, indicating that the presence of the ordered mesoporous structure in aluminosilicates is crucial for the catalysis. The Al-MCM-41 catalyzed Mukaiyama aldol reaction was applicable to a wide range of aldehydes and silyl enol ethers. Furthermore, the Al-MCM-41 catalyst could be recycled at least three times without any loss in the yield. Thus, mesoporous aluminosilicates are promising heterogeneous catalysts for fine chemicals synthesis.     

Activation of ethyl acetate over metal substituted MCM-41: application to alkylation and acylation

Al-MCM-41, Fe,Al-MCM-41 and Zn,Al-MCM-41 materials with different silicon to metal ratios were synthesized hydrothermally and characterized by XRD, BET, FT-IR, Acidity measurement by pyridine adsorbed FT-IR spectroscopy, ²⁹Si and ²⁷Al MAS NMR and ESR techniques. The orderly arrangement of mesoporous materials was clearly revealed from the XRD patterns. ²⁹Si and ²⁷Al MAS NMR established the co-ordination environment of silicon and aluminium. Electron paramagnetic resonance (EPR) study confirmed the co-ordination environment of Fe in Fe,Al-MCM-41 framework. The catalytic activity of these materials was evaluated in the vapour phase alkylation and acylation of ethylbenzene with ethyl acetate in the temperature range between 250 and 400 °C. The products were found to be 1,3-diethylbenzene (1,3-DEB), 1,4-diethylbenzene (1,4-DEB), 1,2-diethylbenzene (1,2-DEB), 4-ethylacetophenone (4-EAP) and acetophenone (AP). The reaction products revealed that activation of ethyl acetate is a convenient route for both alkylation and acylation reactions. The order of the catalysts activity for the reaction is found to be Fe,Al-MCM-41 (50) > Fe,Al-MCM-41 (100) > Zn,Al-MCM-41 (50) > Zn,Al-MCM-41 (100) > Al-MCM-41 (50) > Al-MCM-41 (100). In addition to the density of acid sites, the strength of acid sites is also important for this reaction. The effects of temperature, feed ratio, WHSV and time on stream were also examined and the results are discussed.     

Efficient catalysis of mesoporous Al-MCM-41 for Mukaiyama aldol reactions

Mesoporous aluminosilicates, Al-MCM-41 (Si/Al = 20 and 50), efficiently catalyzed Mukaiyama aldol reaction of benzaldehyde with 1-(trimethylsiloxy)cyclohexene in CH₂Cl₂ at 0 °C to afford the corresponding β-trimethylsiloxy ketone in quantitative yield. On the other hand, mesoporous silica (MCM-41), amorphous SiO₂–Al₂O₃, and H–Y and H-ZSM-5 zeolites barely catalyzed the reaction. Additionally, the less ordered Al-MCM-41 prepared by mechanical compression exhibited much lower catalytic activity compared with Al-MCM-41, indicating that the presence of the ordered mesoporous structure in aluminosilicates is crucial for the catalysis. The Al-MCM-41 catalyzed Mukaiyama aldol reaction was applicable to a wide range of aldehydes and silyl enol ethers. Furthermore, the Al-MCM-41 catalyst could be recycled at least three times without any loss in the yield. Thus, mesoporous aluminosilicates are promising heterogeneous catalysts for fine chemicals synthesis.     

Novel synthesis of ordered mesoporous materials Al-MCM-41 from bentonite

This paper reports the synthesis of ordered mesoporous materials Al-MCM-41 with a specific surface area of 1018 m²/g from bentonite. Pretreated bentonite was simultaneously used as silica and aluminum sources without addition of silica or aluminum reagents. Orthogonal experiments were adopted to optimize the processing parameters. The samples were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), N₂ adsorption–desorption measurements and Fourier transform infrared spectra (FTIR) techniques. The obtained materials were hexagonal Al-MCM-41. Calcination removed the surfactant while new bonds increased the crosslinking of the frameworks. Proper Si/Al molar ratio was critical for the formation of highly ordered mesoporous materials.     

The synthesis of Al-MCM-41 from volclay — A low-cost Al and Si source

The alkaline fusion of volclay (a low-cost sodium exchanged smectite) was used as source to generate the Si and Al components which were effectively transformed into mesoporous Al-MCM-41 depending on hydrothermal condition. The Al-MCM-41 materials were investigated by powder X-ray diffraction (XRD), N₂ adsorption–desorption measurements and both scanning electron microscopy (SEM) and environmental scanning electron microscopy (ESEM). The volclay which converted into a silicon and an aluminium source allowed the formation of well ordered mesoporous Al-MCM-41 materials with high aluminium content (roughly 4 times higher than a Al-MCM-41 produced by a standard method), a high specific surface area (1060 m²/g), a pore volume of 0.8 cm³/g (for pore width < 7.1 nm) with an mono-modal pore distribution with a maximum in the mesoporous pore size of 3.8 nm in pore width.     

Liquid phase catalytic hydrodechlorination of aryl chlorides over Pd–Al-MCM-41 catalyst

Supported Pd catalysts were prepared by direct hydrothermal (DHT) or template-ion exchange (TIE) method on Al-substituted MCM-41 as the support and tested in the hydrodechlorination of aryl chlorides such as 4-chloroanisole in liquid phase, together with impregnated Pd catalysts as references. When Pd was loaded on Al-MCM-41 with the Si/Al ratio of 150 by the TIE method, the catalyst showed the highest activity among the Pd catalysts prepared. PdO originally formed on the catalyst surface was in situ reduced to Pd metal during the reaction as the active form for the dechlorination. The activities of the supported Pd catalysts well correlated with the Pd dispersion on the TIE or impregnated Pd catalysts, whereas the DHT catalysts showed relatively high activities independently on the Pd dispersions. It was confirmed that the dechlorination proceeded by a heterogeneous mechanism catalyzed by Pd metal particles sized less than 10 nm on the surface of the catalyst. Al substitution for Si on MCM-41 was effective for the loading of Pd metal with the high dispersion, none the less Pd was located on the surface of the TIE catalyst particles and no significant effect of mesoporous structure on the reaction was observed. Methanol was the most profitable as the solvent among the various solvents tested. Various types of arylchlorides bearing hydroxy, methoxy, methyl, nitro and phenylcarbonyl group at the p-position were efficiently dechlorinated over Pd–Al-MCM-41 catalyst at 40 °C. Electrophilic attack of arylchloride was proposed as the rate determining step, where ionic mechanism positively worked and electron-releasing substituents increased the catalytic activity.     

Characterization and catalytic performance of mesoporous molecular sieves Al-MCM-41 materials

Mesoporous Al-MCM-41 materials of different Si/Al ratios have been synthesized and characterized by X-ray powder diffraction, ²⁷Al and ²⁹Si MAS NMR, differential thermogravimetric analysis, N₂ adsorption measurements, FT-IR and catalytic cracking of alkanes. The experimental results show that the incorporation of aluminium into the framework of MCM-41 has a great effect on the degree of long-distance order, the surface acidities and the mesoporous structures of the materials. With increase of the aluminium content, the amounts of tetrahedral framework aluminium and the acid sites on the samples increase, but the acid strength decreases. Al-MCM-41 materials exhibit high activity for n-C₁₆ ⁰ cracking and good selectivity for producing low carbon alkylenes, particularly for i-C₄ ⁼.     

助剂掺杂对Fe—MCM-41在环己烷氧化反应中催化性能的影响

z以硅酸钠为硅源，十六烷基三甲基溴化铵为模板剂，硝酸铁为金属源，水热法直接合成Fe—MCM-41，再辅以助剂co和cr形成双金属掺杂的介孔材料，采用XRD、N2吸脱附、TG—DTA、FTIR、ICP对材料的结构和物化性质进行表征。以乙腈为溶剂，H2O2为氧化剂，考察所制备的材料对环己烷氧化的催化活性和选择性的影响。结果表明，与Fe—MCM41的催化性能相比，FeCo—MCM41会使环己烷的转化率下降，但环己醇的选择性增加；而FeCr—MCM41会使环己烷的转化率和环己酮的收率增加。     

Catalytic activity of mesoporous catalysts in Friedel–Crafts benzylation of benzene

Different samples of metal-incorporated MCM-41 were prepared and used as catalysts in Friedel–Craft’s benzylation of benzene. The catalytic performance was evaluated by off-line GC analysis. Fe-MCM-41 exhibited excellent activity, the sample with Si/Fe ratio = 10 showed 90% conversion with 95% selectivity towards diphenylmethane within a few minutes. Generally, the activity per Fe-site was an order of magnitude higher for the samples containing a combination of Fe₂O₃ nano-particles and isolated Fe³⁺ sites. A synergy of two catalytic centers (particles and isolated sites) is proposed to explain the high performance of the highly loaded samples. The catalytic performance of Fe-MCM-41 was superior to other metal-containing MCM-41 (e.g. Ga, Sn, and Ti) catalysts, or other Fe-containing mesoporous materials (e.g. Fe-HMS).     

Distribution and properties of catalytically active Cu-sites on a mesoporous MCM-41 silicate modified by Al, Zr, W, B, or P ions

Pure SiO₂ having a MCM-41 structure was modified by the introduction of 1 mmol/g of Al, Zr, W, B, or P. The parent silica and the modified materials were used to support a dispersed cupric oxide. The distribution, properties and thermal stability of the catalytic Cu²⁺-active sites were examined by ESR and IR spectroscopy and by measuring the activity in a test reaction of ethane oxidation. Modification of the parent silica MCM-41 influences drastically the stabilization of isolated Cu²⁺-species. Al-MCM-41 provides the most disperse (70–80%) and thermally stable state of the cupric phase. However, no simple correlation exists between the total number of surface Cu²⁺-sites and the catalytic activity. The specific catalytic activity (per one Cu²⁺-active site accessible to the reactants) depends strongly on the structure of the localized site. Isolated Cu²⁺-sites grafted to Al-MCM-41 show relatively high activity for the sample calcined at 520 °C. Thermal treatment at 650–750 °C causes a sharp loss of specific Cu²⁺ catalytic activity of Cu/Al-MCM-41 (as is also the case with CuH-ZSM-5). The less disperse cupric phase in non-modified MCM-41 demonstrates a higher specific catalytic activity.     

Zr (IV)-ninhydrin supported MCM-41 and MCM-48 as novel nanoreactor catalysts for the oxidation of sulfides to sulfoxides and thiols to disulfides

Modification of MCM-41 and MCM-48 mesoporous materials with bonded aminosilane species, Schiff base preparation by ninhydrin and finally complexation with zirconium, has attracted much attention in order to design catalyst with advanced applications in the oxidation of sulfides to sulfoxides and thiols to disulfides in the presence of hydrogen peroxide. In all oxidation of sulfides to sulfoxids 0.4 mL H₂O₂ used as oxidant in the presence of Zr(IV)-ninhydrin supported MCM-41 (0.01 g) or Zr(IV)-ninhydrin supported MCM-48 (0.005 g) at room temperature and solvent-free condition. Also the best conditions for oxidation of thiols to disulfides with 0.4 mL H₂O₂ were 0.005 g Zr(IV)-ninhydrin supported MCM-41 or Zr(IV)-ninhydrin supported MCM-48 at room temperature and in ethanol. These catalysts are characterized by SEM, XRD, TGA, FT-IR, EDS, ICP and BET analysis. Also the Turn over frequency (TOF) and Turn over number (TON) of catalysts are calculated. Obtained results by these heterogeneous catalysts revealed several advantages including short reaction times, simple workup, easy isolation and reusability.     

Highly hydrothermally stable Al-MCM-41 with accessible void defects

Mesoporous aluminosilicates (Al-MCM-41) with high hydrothermal stability were synthesized via self-assembly of nanoseed precursors, obtained from alkali-treatment of ZSM-5. Characterized by N₂ sorption, Transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and Mercury intrusion, as-prepared Al-MCM-41 possessed a large number of void defects, enhancing the connectivity of MCM-41. The effects of alkali-treatment degree, including time and concentration, on volume of void defects were investigated and discussed. It is revealed that volume of void defects decreased in the severe condition of alkali-treatment, and void defects representing the intraparticular pores account for a volume of 0.138 cm³/g in Al-MCM-41, prepared under the condition of 1.0 mol/L of NaOH and 1 h of stirring time. A tentative proposed mechanism for interpreting the formation of void defects was presented. Aggregated secondary building units in the precursors not only provided Si (Al) sources, but also functioned as templates for the development of void defects. Al-MCM-41 with void defects would be beneficial to diffusion and mass transportation.     

Synthesis of dypnone using SO4/Al-MCM-41 mesoporous molecular sieves

The mesoporous molecular sieves Al-MCM-41 with Si/Al ratio equal to 16, was synthesized under hydrothermal conditions using cetyltrimethylammonium bromide (CTMA⁺Br⁻) as surfactant. The same ratio of Al-MCM-41 materials was impregnated using sulfuric acid, the materials as sulfated Al-MCM-41 (SO₄²⁻/Al-MCM-41). The mesoporous materials viz Al-MCM-41 and SO₄²⁻/Al-MCM-41 were characterized using several techniques e.g. ICP-AES, Nephelometer, XRD, FT-IR, TG/DTA, N₂-adsorption, solid-state-NMR, SEM and TPD-pyridine. ICP-AES studies indicated the presence of Al in the mesoporous materials. Nephelometer studies indicated the SO₄²⁻ presence of the SO₄²⁻/Al-MCM-41. XRD studies indicated that the calcined materials of Al-MCM-41 and SO₄²⁻/Al-MCM-41 had the standard MCM-41 structure. The surface area, pore diameter, pore volume and wall thickness of the mesoporous materials were calculated by BET and BJH equations, respectively. Crystallinity, surface area, pore diameter and pore volume of SO₄²⁻/Al-MCM-41 decreased except wall thickness and the expelling aluminum from the Al-MCM-41 framework increased the Lewis acidity. FT-IR studies indicated that Al-ions were incorporated in the hexagonal mesoporous structure of Al-MCM-41 and sulfuric acid was impregnated into hexagonal Al-MCM-41 materials. The thermal stability of as-synthesized Al-MCM-41 materials and SO₄²⁻/Al-MCM-41 materials were studied using TG/DTA. The environments of the Al-ions coordinated in the silica matrix were determined by ²⁷Al-MAS-NMR. The morphology of Al-MCM-41 and SO₄²⁻/Al-MCM-41 was determined by SEM. The total acidity of Al-MCM-41 and SO₄²⁻/Al-MCM-41 materials was determined by TPD-pyridine. The catalytic results were compared with those obtained by using sulfuric acid, amorphous silica–alumina, H-β, USY and H-ZSM-5 zeolites. The SO₄²⁻/Al-MCM-41 catalyst exclusively forms the product of dypnone from self-condensation of acetophenone molecules due to higher number of Lewis acid sites and has much higher yields than other catalysts except USY.