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.     

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.     

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.     

Room temperature efficacious synthesis of diphenylmethane over Fe/Al-MCM-41 catalysts

Fe/Al-MCM-41 (Si/Al = 25, 50, 75 and 100) were synthesized. Their catalytic activity was evaluated towards benzylation of benzene with benzyl chloride in liquid phase. The catalytic activity of Fe/Al-MCM-41(25) was higher than the other catalysts. Diphenylmethane(DPM) was obtained as the major product with 100% selectivity and with 100% conversion of benzyl chloride under optimum condition. The effect of temperature and the feed ratio, on the activity of Fe/Al-MCM-41(25) and selectivity towards DPM was studied and a possible reaction mechanism was proposed.     

Al-MCM-41介孔分子筛吸附喹啉的性能

在碱性条件下,采用水热晶化法,以偏硅酸钠为硅源,铝酸钠为铝源,CTAB为结构模板剂,成功合成出了含铝介孔分子筛Al-MCM-41。采用XRD、BET等手段对合成的Al-MCM-41进行表征,对柴油中的氮化物喹啉进行了吸附实验,考察了Al-MCM-41介孔分子筛对氮化物喹啉的吸附能力,探究了硅铝比为60的Al-MCM-41分子筛对喹啉溶液吸附的热力学和动力学行为,测得353.15～393.15 K 温度范围内的吸附等温线数据,用Langmuir、Freundlich方程对此进行拟合,并根据热力学原理计算得到吸附过程中的ΔH、ΔG、ΔS值和吸附表观活化能。结果表明, 硅铝比为60的Al-MCM-41具有较大的孔容、比表面积和较窄的孔径分布,结晶度和有序性高。等温吸附平衡符合Freundlich 等温线模型,其ΔH -0.7682 kJ·mol^-1,ΔG -28.1215 kJ·mol^-1, ΔS 73.2434 J·mol^-1·K^-1,吸附动力学符合Pseudo拟二级方程,E_a为2.8575 kJ·mol^-1。     

Surface and bulk investigation of ZSM5 and Al-MCM-41 using synchrotron XPS, XANES, and hexane cracking

We present a comparative study of ZSM5 and Al-MCM-41 catalysts using spectroscopic and chemical techniques. The analysis of conventional and synchrotron XPS spectra of these catalysts reveals the presence of a topmost surface-related Si peak in addition to the bulk peak. XANES results suggest structural modification upon heating Al-MCM-41 at 500 °C. Depth-resolved XPS data show Al depletion from the surface of Al-MCM-41 in contrast to surface enrichment of Al in ZSM5. These surface modifications could be one of the reasons for the weak acidity of Al-MCM-41 in chemical reactions such as hexane cracking at different temperatures.     

Al-MCM-41介孔分子筛深度吸附脱硫的研究

以十六烷基三甲基溴化铵为模板剂、铝酸钠为铝源、硅酸钠为硅源、用水热合成法制备了不同硅铝比的Al-MCM-41分子筛,负载不同金属离子对其改性,并用X射线衍射仪(XRD)、N2气吸附等方法对其进行了表征。同时,考察了Al-MCM-41(80)负载不同金属离子作为吸附剂对模拟汽油的脱硫性能。结果表明,Al-MCM-41(80)在353 K时的脱硫效果最好;负载金属离子Fe3+、Ni2+、Zn2+、Cu2+、Co2+、Ce3+的脱硫效果顺序为:Ni2+>Co2+>Zn2+>Fe3+>Ce3+>Cu2+;芳烃的加入降低了分子筛对噻吩的选择性。     

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%。     

Hybrid zeolitic-mesostructured materials as supports of metallocene polymerization catalysts

The potential application of hybrid ZSM-5/Al-MCM-41 zeolitic-mesostructured materials as supports of metallocene polymerization catalysts has been investigated and compared with the behaviour of standard mesoporous Al-MCM-41 and microporous ZSM-5 samples. Hybrid zeolitic-mesostructured solids were prepared from zeolite seeds obtained with different Si/Al molar ratios (15, 30 and 60), which were assembled around cetyltrimethylammonium bromide (CTAB) micelles to obtain hybrid materials having a combination of both zeolitic and mesostructured features. (nBuCp)₂ZrCl₂/MAO catalytic system was impregnated onto the above mentioned solid supports and tested in ethylene polymerization at 70 °C and 5 bar of ethylene pressure. Supports and heterogeneous catalysts were characterized by X-ray powder diffraction, nitrogen adsorption-desorption isotherms at 77 K, transmission electron microscopy, ²⁷Al-MAS-NMR, ICP-atomic emission spectroscopy and UV-vis spectroscopy.Catalysts supported over hybrid ZSM-5/Al-MCM-41 (Si/Al = 30-60) exhibited the best catalytic activity followed by those supported on Al-MCM-41 (Si/Al = 30-60). However, catalyst supported on ZSM-5 gave lower polymerization activity because of its microporous structure with narrower pores and lower textural properties than hybrid and mesoporous materials.Although higher acid site population shown by hybrid materials could contribute to the stabilization of the metallocene system on the support, in this case their better catalytic performance is mainly ascribed to the larger textural properties.     

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.     

Uptake of decontaminating agent from aqueous solution: a study on adsorption behaviour of oxalic acid over Al-MCM-41 adsorbents

Hydrothermal method was followed to synthesis the mesoporous Al-MCM-41 (Si/Al = 25, 50, 75 and 100) and Si-MCM-41 molecular sieves using a cetyltrimethylammonium bromide as a surfactant and the materials were unambiguously characterized by XRD, N₂ sorption studies, ²⁷Al MAS-NMR and TEM. The removal of oxalic acid from aqueous solution was studied through an adsorption process because oxalic acid may cause complexes with radioactive cations during decontamination operation in nuclear industry, which resulting in interferences in their removal by conventional treatment. Adsorption of oxalic acid over Al-MCM-41 shows the applicability of Langmuir isotherm and follows first order kinetics. The effects of parameters such as contact time, concentration of oxalic acid, adsorbents (various Si/Al ratios of Al-MCM-41, Si-MCM-41 and activated charcoal) and pH have been investigated to yield higher removal of oxalic acid. The percentage of oxalic acid adsorbed per unit gram of adsorbent for Al-MCM-41 at Si/Al = 100, 75, 50 and 25, Si-MCM-41, and activated charcoal are 34.6, 40.9, 51.4, 61.3, 16.1 and 60, respectively. Retainment of crystallinity and absence of structural collapse of Al-MCM-41 after desorption and adsorption of oxalic acid, respectively has been achieved in this study.     

Effect of lanthanum addition on the thiophene hydrodesulfurization activity over Al-MCM-41 supported molybdenum catalysts

A series of Al-MCM-41 modified with 1–7% lanthanum were used as supports to prepare the Mo/La–Al-MCM-41 catalysts containing 10 wt.% molybdenum. The supports and catalysts were characterized with XRD, BET, XPS, TPD, TEM and SEM, and their catalytic activities were tested for thiophene hydrodesulfurization. The La addition did not cause any significant collapse of the structure and morphology of Al-MCM-41 samples, and increased the acidity of Al-MCM-41 samples. The Mo/La–Al-MCM-41 catalysts showed higher thiophene HDS activity than non-modified catalysts. The La-modified catalysts showed an enhanced butene selectivity but a decreased tetrahydrothiophene selectivity, indicating that the La–Al-MCM-41 supports contained a larger amount of acid sites.     

Cobalt oxide nanoparticles on mesoporous MCM-41 and Al-MCM-41 by supercritical CO2 deposition

CoO and Co₃O₄ nanoparticles were uniformly dispersed inside mesoporous MCM-41 and Al-MCM-41 supports using supercritical CO₂ reactive deposition. This method represents a one-pot reproducible procedure that allows the dissolution of the organocobalt precursor and supports impregnation in supercritical CO₂ at 70 °C and 110 bar, followed by the precursor thermal decomposition into cobalt species at 200 °C and 160 bar. By the relative concentration of the cobalt precursor [cobalt (II) bis (η⁵-ciclopentadienil)], the load of cobalt nanoparticles was controlled and then determined by Inductively Coupled Plasma (ICP-OES). The synthesis of CoO and Co₃O₄ species inside the MCM-41 and Al-MCM-41 substrates was confirmed by X-ray Photoelectron (XPS) and Laser Raman Spectroscopies (LRS). By N₂ adsorption and Small Angle X-ray Scattering (SAXS), it was determined that the hexagonal arrangement as well as the surface area and pore size of the substrates changed after the addition of cobalt. By means of X-ray mapping from SEM images, a homogeneous distribution of cobalt nanoparticles was observed inside the mesopores when the cobalt loading was 1 wt.%. In addition, spherical cobalt nanoparticles of average diameter close to 20 nm were detected on the outer surface of MCM-41 and Al-MCM-41 supports when the cobalt content was higher. On the other hand, by Transmission Electron Microscopy (TEM), it was possible to measure the interplanar distance of the crystalline plane of the outer nanoparticles, which was later compared with the theoretical distance values which allowed identifying the CoO and Co₃O₄ phases.     

Al-MCM-48 as a potential hydrotreating catalyst support: I – Synthesis and adsorption study

The work has been focused on utilizing mesoporous alumina MCM-48 material as a potential hydrotreating catalyst support for light-cycle oil (LCO) and exploring its adsorption ability for large aromatics. A series of Al-MCM-48 samples with various Si/Al ratios was synthesized via a hydrothermal method and characterized with X-ray diffraction (XRD), nitrogen adsorption isotherms, solid NMR, etc. The adsorption equilibrium isotherms of typical aromatics in LCO such as diaromatic 1-methylnaphthalene on Al-MCM-48 and MCM-48 samples were studied by a standard gravimetric technique. Compared with parent MCM-48, Al-MCM-48 samples exhibited higher adsorption capacity and stronger adsorption affinity towards the addressed aromatic compounds. The incorporation of alumina into MCM-48 materials generated acid centers and more hydroxyl groups on the support surface, which can provide enhanced adsorption for the sorbate molecules and dispersion of active phases. It was found that the adsorption behaviors of the aromatic compounds in Al-MCM-48 samples were mainly governed by the acidity of the support. The balance between pore volume and acid strength of Al-MCM-48 can be adjusted by altering Si/Al ratio. The influence of incorporation of Al on the framework and adsorption properties of the materials has also been investigated.     

Multiwalled carbon nanotubes synthesis with high yield utilizing Pt/Al-MCM-41 via catalytic chemical vapour deposition technique

Multiwalled carbon nanotubes (MWNTs) were synthesized over Pt impregnated Al-MCM-41 catalyst by decomposition of acetylene and characterized by XRD and nitrogen sorption isotherm to study the mesophase nature of the material. The optimum temperature and flow rate of the carbon source for CNTs synthesis are 800 °C and 60 mL/min, respectively, within a short reaction period, typically 10 min. Moreover, longer reaction time (i.e. 30 min) favours the formation of more amorphous carbon. When the reaction time is reduced to less than 10 min, formation of amorphous carbon is greatly suppressed by the high yield of MWNTs (85%). The products obtained from the decomposition of acetylene over these catalysts were characterized by TGA, SEM, TEM and Raman spectroscopy. The TEM analysis reveals that CNTs are free from amorphous carbon, whereas Raman spectrum shows two prominent peaks at 1,327 and 1,594 cm⁻¹ as the tangential modes of CNTs. As a conclusion, Pt/Al-MCM-41 is an effective template for MWNTs synthesis using acetylene as a carbon source.     

Al-MCM-41分子筛对多环烃的催化异构化性能

采用室温法合成了Al-MCM-41分子筛，采用XRD、FT-IR和表面测定仪等方法表征了Al-MCM-41分子筛的结构。以多环烃endo-TCD（桥式四氢双环戊二烯）异构化反应为例考察了不同铝硅物质的量比的Al-MCM-41分子筛催化异构化性能，在此基础上研究了表面负载无机酸及贵金属Pt的促进作用。结果表明，Al-MCM-41分子筛对endo-TCD具有良好的催化异构化作用，无机酸的负载对催化剂活性和提高金刚烷收率具有一定促进作用，而采用化学还原法负载Pt则未达到预期目的。     

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.     

Al-MCM-41 catalyzed decomposition of polypropylene and hybrid genetic algorithm for kinetics analysis

Mesoporous catalysts (Al-MCM-41) are synthesized by sol–gel and hydrothermal methods to study their effects on the catalytic decomposition of polypropylene (PP) sample. The catalysts are characterized by X-ray diffraction (XRD) analysis and nitrogen adsorption study. Since sol–gel Al-MCM-41 catalyst shows better catalytic activity, further experimental studies were conducted to find its reusability and its activity at five different heating rates. The constant pattern behaviour of the TG curves for different catalyst percentages possibly suggests existence of similar reaction mechanism where large polymer fragments are cracked on the external surface of the catalyst and then enters into the mesopores for further cracking. Thus, presence of catalyst surfaces not only converts the polymer into comparatively smaller fractions, but also makes the decomposition of PP energy effective. Kinetics parameters are estimated based on 15 different decomposition models and the multi-heating rate experimental data both for catalytic and noncatalytic decomposition of PP using hybrid genetic algorithm (HGA). Suitability of the model is tested using corrected Akaike's Information Criteria (AIC_c). Results show that Nucleation and Growth model better predicted the experimental TGA data. However, nth order model also shows good AIC_c score and well predicted the experimental TGA data. Thus, though apparently it seems that Nucleation and Growth model controls the decomposition of PP sample, further investigation in detail including infrared or mass spectroscopy, morphology study using SEM or TEM during such decomposition is very much essential to conclude upon the actual reaction mechanism that controls decomposition of PP sample.     

Vapour phase esterification of butyric acid with 1-pentanol over Al-MCM-41 mesoporous molecular sieves

Al-MCM-41 molecular sieves with Si/Al ratios 25, 50, 75 & 100 were synthesized hydrothermally and characterized systematically by various analytical and spectroscopy techniques. Their catalytic activity was evaluated for the vapour phase reaction of butyric acid with 1-pentanol. Pentyl butyrate was obtained as the only product. Reaction parameters such as temperature, molar ratio and feed rate were optimized for higher butyric acid conversion. The time-on-stream study was carried out at optimum conditions resulting in gradual decrease in the activity of the catalyst.     

Efficient Activation of Coal Fly Ash for Silica and Alumina Leaches and the Dependence of Pb(II) Removal Capacity on the Crystallization Conditions of Al-MCM-41

In this study, four different coal fly ashes (CFAs) were used as raw materials of silica and alumina for the preparation of the alumina-containing Mobil Composition of Matter No. 41 (Al-MCM-41) and the exploration of an activation strategy that is efficient and universal for various CFAs. Alkaline hydrothermal and alkaline fusion activations proceeded at different temperatures to determine the best treatment parameters. We controlled the pore structure and surface hydroxyl density of the CFA-derived Al-MCM-41 by changing the crystallization temperature and aging time. The products were characterized by small-angle X-ray diffraction, nitrogen isotherms, Fourier-transform infrared spectroscopy, ²⁹Si silica magic-angle spinning nuclear magnetic resonance, and transmission electron microscopy, and they were then grafted with thiol groups to remove Pb(II) from aqueous solutions. This paper innovatively evaluates the CFA activation strategies using energy consumption analysis and determines the optimal activation methodology and parameters. This paper also unveils the effect of the crystallization condition of Al-MCM-41 on its subsequent Pb(II) removal capacity. The results show that the appropriate selection of crystallization parameters can considerably increase the removal capacity over Pb(II), providing a new path to tackle the ever-increasing concern of aquic heavy-metal pollution.