Aluminosilicate MCM-41 Research Articles

Effective removal of fluorine ions in phosphoric acid by silicate molecular sieve synthesized by hexafluorosilicic acid

Silicone zeolite prepared from hexafluorosilicic acid is a good adsorbent for fluoride removal. The morphology and structure of the prepared composites were characterized by XRD, FT-IR and BET. XRD images showed that fluorine was adsorbed on the surface of zeolite and the FT-IR spectra showed that there are different kinds of silicon and aluminum in silica-based zeolite. Therefore, through the studied of regeneration-adsorption cycle of zeolite, fluoride desorption and regeneration mechanism of zeolite defluorination was explained, and the adsorption performance and regeneration adsorption performance of zeolite defluorination were evaluated. The effects of phosphoric acid concentration, operating condition and specific surface area of zeolite and Si/Al ratio of zeolite on adsorption performance were investigated. Silicate molecule sieve shows strong adsorption capacity for fluoride (F-), and the adsorption capacity reached 352.46 mg/g under the optimal conditions. The Freundlich and Langmuir isotherm models for aluminosilicate MCM-41 and NaA zeolite which experimental data of F- adsorption on in phosphoric acid were fitted to investigate the adsorption mechanism. In the mechanism of anion adsorption, F- or SiF62- is bound by electrostatic adsorption of hydroxyl on the surface of adsorbent with anion adsorption. The adsorbed SiF62− ions can be regenerated when the environmental pH increases to value higher than that of zero charge point of zeolite. There is a competitive adsorption between OH– and F- with negative charge, which reduces the adsorption efficiency of adsorbent for F-. The NaA zeolite regenerated with NH3·H2O showed better fluorine re-adsorption performance.

Unprecedented improvement of the hydrothermal stability of amine-grafted MCM-41 silica for CO2 capture via aluminum incorporation

The hydrothermal stability of amine-containing CO2 adsorbents is of paramount importance as steam stripping is often practiced for regenerating CO2-loaded materials. The impact of aluminum incorporation into the structure of MCM-41 silica on its adsorptive properties and hydrothermal stability during CO2 capture was studied. Large-pore MCM-41 silica and MCM-41 aluminosilicate (Si/Al = 15) supports with similar average pore sizes of 64 and 66 Å, respectively, were synthesized using a novel method. Amine functionalization of the supports was conducted using grafting of triamine under dry and wet conditions. Amine-tethered MCM-41 aluminosilicate adsorbents exhibited higher CO2 uptakes (up to 63% higher after 60 min of adsorption at 25 °C) and faster CO2 adsorption kinetics (up to 71% faster after two minutes of adsorption at 25 °C) relative to their MCM-41 silica counterparts. Following a three-hour exposure to steam, extensive deterioration of adsorptive properties was observed for the triamine-grafted MCM-41 silica materials, particularly at low adsorption temperatures of 25 and 50 °C, showing CO2 uptake losses as high as 73 and 56%, respectively. The triamine-grafted MCM-41 aluminosilicate materials, however, showed unprecedented hydrothermal stability with no significant drop in CO2 uptake (respective losses as high as 27 and 17%) and adsorption kinetics. After steam stripping, N2 adsorption-desorption measurements at 77 K showed significantly higher reductions in the Brunauer-Emmett-Teller surface area of the triamine-grafted MCM-41 silica materials (losses of 36–49%) compared to their MCM-41 aluminosilicate counterparts (losses of 31 to 35%). It is inferred that aluminum incorporation into the support increases the hydrothermal stability of the resulting grafted materials in the presence of steam.

Hierarchical ZSM-5 based MCM-41 aluminosilicates: Ostwald ripening effect of 8 years old aged samples

MCM-41 with zeolitic nanocomposite has been reported to reduce diffusional restrictions, strengthen structural stability of mesophase and improve acidity. Here we study the natural growth process known as Ostwald ripening effect over composite zeolite particles with aging time. Three different MCM-41/ZSM-5 composites were studied along with conventional AlMCM-41 (AlM41) that are stored for 5 and 8 years. Textural features of MCM-41 with proto-zeolitic nanoclusters at pore walls (ZMST2), ZSM-5/MCM-41 composite with equiproportion mixture of meso and microphases (50 wt%) (ZM27), disordered hexagonal/ZSM-5 composite (ZM23), and AlMCM-41 were compared using x-ray diffraction (XRD), nitrogen adsorption isotherm, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), 27Al MAS NMR, scanning electron microscope (SEM) and transmission electron microscope (TEM). Calcined AlMCM-41 showed aging stability, while calcined ZMST2 showed high Ostwald ripening effect. The disordered hexagonal surface area and pore volume of ZMST2 increase to ∼54% and ∼68% compared to fresh ZMST2. Remarkably, aging in as-synthesised form (A-ZMST2) slowed down the Ostwald process and improved hexagonal thermal stability at 550 °C and 800 °C. ZM27 exhibited high aging stability even in calcined form. The surface area showed about 92% of retainment with an increase in the pore volume (∼20%). ZM23 with disordered hexagonal structure showed that aging period of 5 years decreases meso and increases micropore characters of ZSM-5. Overall, the study shows Ostwald ripening effect dominates over calcined ZMST2, while A-ZMST2 and A-ZM27 in as-synthesised form are able to withstand the structural collapse during long shelf time. Prolonged aging rearranges aluminium coordination environment similar to micropore environment of ZSM-5. The study will further help to understand the atmospheric moisture interactive process with hierarchical zeolites and facilitate preventive measures for long-term industrial applications.

Bifunctional MCM-41 aluminosilicate supported Ir with adjusted metal and acid functionality for catalytic ring opening of 1,2-dimethylcyclohexane

Herein we report H-AlMCM-41 aluminosilica supported Ir materials with adjusted acid/metal function as bifunctional catalysts for selective ring opening (RO) of 1,2-dimethylcyclohexane (1,2-DMCH) at 330°C and 3MPa to primary ring opening products (P-ROP), which are defined as C8 alkanes. Large-pore H-AlMCM-41 materials were synthesized with Si/Al atomic ratios of 20 and 45 and impregnated for the first time with 0.6–1.8wt% Ir to afford xIr/H-Al-MCM-41(y) bifunctional catalysts (x=Ir content in wt%, y=Si/Al ratio) with moderate Brønsted acidity and relatively strong hydrogenolysis tendency. The optimum catalytic performance was achieved with 1.2Ir/H-AlMCM-41(45), which gave 31% yield of desired alkane products at 71% conversion of 1,2-DMCH. In contrast, zeolite based 0.5Ir/H-Beta-25 as well as the purely metallic 0.7Ir/Na-AlMCM-41(20) catalysts did not exhibit suitable catalytic performance for the production of C8 alkanes compared to Ir/H-AlMCM-41 catalysts. All materials were thoroughly characterized by N2 adsorption, solid-state NMR, TEM and FTIR of adsorbed pyridine, and their catalytic behavior was discussed in light of their physiochemical properties.

Hydrocracking of bio-alkanes over Pt/Al-MCM-41 mesoporous molecular sieves for bio-jet fuel production

Bi-functional catalysts consisting of platinum on aluminosilicate MCM-41 materials with Si/Al ratios between 10 and 30 were prepared via direct mixed-gel synthesis. The catalysts were tested in the hydrocracking of bio-alkanes, produced from biodiesel hydrodeoxygenation and composed of n-hexadecane and n-octadecane, for the production of bio-jet fuel. The effects of temperature, pressure, weight hourly space velocity (WHSV), and H2/n-paraffin weight ratio on bio-alkanes conversion and product distribution were examined. The conversion was found to be dependent on the acid strength of the catalyst supports which were proportional to the Al content. However, the catalyst selectivity decreased with the increasing Al content. The optimal Si/Al ratio, temperature, pressure, WHSV, and H2/n-paraffin weight ratio were determined to be 20, 330 °C, 2 MPa, 1 h−1, and 0.20, respectively. Under these conditions, the bio-alkanes conversion and kerosene/gasoline ratio in the product reached 65.62% and 1.96, respectively.

Template-Induced Nucleation of Isonicotinamide Polymorphs

By studying the potential of different heterogeneous templates to stimulate heterogeneous nucleation, this work aims to enhance the current knowledge of heterogeneous nucleation mechanisms and to obtain improved control of polymorphic selectivity in solution crystallization. The possibility of inducing nucleation of different isonicotinamide (INA) polymorphs by using heterogeneous templates, exhibiting porous and regular surfaces structures in the nanometer range, such as synthetic zeolite ZSM-5, mesoporous aluminosilicate MCM-41, and TiO2 in both rutile and anatase phase, was investigated by monitoring in real-time the course of the crystallization process. Experiments demonstrated that all used templates were effective in reducing induction time, thus being successful in enhancing the nucleation rate of INA. Furthermore, the ability of the TiO2 template in anatase form to induce the formation of a mixture of metastable forms I and III, thus diverting the expected course of polymorph crystallization due to INA self-association in ethanol, was demonstrated, providing an additional tool to achieve polymorphic selectivity in solution crystallization.

Modifier-enhanced supercritical CO2 extraction of organic template from aluminosilicate MCM-41 materials: Effect of matrix Al/Si ratios and different modifiers

The introduction of polar modifiers usually can make supercritical CO2 extraction more attractive in various potential applications. In this work, modified SCCO2 extraction has been investigated for removing the template cetyltrimethylammonium bromide (CTMABr) from newly synthesized aluminosilicate MCM-41 materials. The effects of the modifier identity and matrix Al/Si ratio on the extraction efficiency and material structural properties are then investigated in detail through numerous characterization methods. The results shows that the incorporation of aluminum into the MCM-41 framework has led to considerable decrease in the extraction efficiencies and the efficiencies are observed to decrease as the Al/Si molar ratio increases arising from the strong interactions between the template and the Al species incorporated into the matrix. Methanol modifier has resulted in much higher extraction efficiencies in the range of 60–87% depending on the Al/Si molar ratio in the sample matrix. Nitrogen adsorption/desorption and XRD results shows that the modifier identity and matrix Al/Si ratio have strongly influenced the structural properties of resultant mesoporous materials. Friedel–Crafts acylation reaction of 2-methoxynaphthalene has been analyzed through gas chromatography and the results show that the sample treated with SCCO2 extraction modified with acetic methanol is more catalytically active than the directly calcined counterpart.

Hydrodesulfurization of Dibenzothiophene over MCM-41-Supported Pd and Pt Catalysts

Three series of aluminosilicate MCM-41 (Al-MCM-41) were synthesized using different aluminum sources, including aluminum isopropoxide (AlM-I), pseudoboehmite, and aluminum sulfate, by a hydrothermal method. The hydrodesulfurization (HDS) performance of the Al-MCM-41-supported Pd and Pt catalysts prepared with chlorided precursors were evaluated with dibenzothiophene (DBT) as the model sulfur-containing molecule, in comparison with those supported on a siliceous MCM-41 (SiM). Pd/SiM and Pt/SiM were not promising for DBT HDS because of their relatively low activities and the rapid irreversible deactivation. Pd and Pt supported on the acidic Al-MCM-41 materials showed higher dispersion and enhanced HDS performances. AlM-I, which possessed the strongest acidity, was the most promising among the mesoporous materials investigated. The deactivated Pd/AlM-I and Pt/AlM-I can be reversibly regenerated by H2 reduction. DBT HDS over the Pd catalysts predominantly took the hydrogenation (HYD) pathway, whereas the direct desulfurization (DDS) pathway and HYD pathway were comparable for the Pt catalysts. Increasing the support acidity had no positive effect on the DDS activity of Pd but significantly enhanced its HYD activity, while the increase in the rate constant of DDS pathway was close to that of the HYD pathway for Al-MCM-41-supported Pt catalysts. The effect of the acid properties of the supports on the HDS performance of Pd and Pt catalysts was discussed by considering the formation of “electronic-deficient” particles and the hydrogen spillover process.

Calorimetric study of mesoporous solids at room temperature

Mesoporous aluminosilicate molecular SBA-15, SBA-16, MCM-41 and MCM-48 were synthesized using standard procedures. The products were characterized by powder X-ray diffraction (XRD), diffuse reflectance Fourier-transform infrared (DRIFT), nitrogen sorption and immersion microcalorimery. The walls of the mesopores are essentially crystallinity, and the local atomic arrangement is similar to that in amorphous aluminosilicates. On the other hand, the immersion enthalpies in solvents polar and non-polar are a function of the accessible area of each of mesoporous solids.

Synthesis and characterization of ionic liquid-functionalized alumino-silicate MCM-41 hybrid mesoporous materials

Ionic liquid-functionalized alumino-silicate MCM-41 hybrid mesoporous materials have been synthesized with two-step approach, by means of in situ skeleton doping with aluminium and post surface grafting with N-methylimidazole ionic liquid groups. The samples were characterized by X-ray diffraction (XRD), high resolution transmission electron microscope (HRTEM), N2 adsorption–desorption, Fourier transform infrared (FTIR) spectra, 27Al and 13C MAS NMR spectra and temperature-programmed desorption (TPD) of NH3. The results indicated that the bifunctionalized MCM-41 possessed ordered mesostructure. Aluminium was efficiently introduced into the framework of the mesostructure, generating Lewis and Brönsted acid sites. N-methylimidazole ionic liquid groups were covalently grafted onto the surface of mesoporous materials. The as-synthesized bifunctional MCM-41 showed good catalytic performance in the coupling reaction of CO2 and propylene oxide.

ChemInform Abstract: Preparation of Aluminosilicate MCM-41 in Desirable Forms via a Novel Co-Assemble Route.

A new alkali-free synthesis system allows us to prepare aluminosilicate MCM-41 directly in a variety of desirable forms: M-AlMCM-41 (M=H, Cu, Zn, Cd, Ni), the solution ion-exchange and subsequent calcination being avoided; the formation is discussed in terms of a co-assemble process.

Hydrodesulfurization of dibenzothiophene catalyzed by Pd supported on overgrowth-type MCM-41/HY composite

Siliceous MCM-41 (Si-MCM-41), aluminosilicate MCM-41 (Al-MCM-41) and two micro-mesoporous materials obtained either by physically mixing Si-MCM-41 with HY zeolite [MY(M)] or by overgrowing Si-MCM-41 over HY zeolite particles [MY(C)], were prepared and characterized by means of XRD, XRF and pyridine adsorbed FT-IR. The hydrodesulfurization (HDS) performances of the supported Pd catalysts were evaluated with dibenzothiophene (DBT) as the model sulfur-containing molecule. The results indicated that the HDS performances of Pd catalysts are significantly influenced by the pore structures and acid properties of the supports. Pd catalysts supported on the acidic supports showed enhanced stability as well as HDS and hydrogenation (HYD) activities. Among the catalysts studied, Pd/MY(C) exhibited the highest activity and stability in DBT HDS. Its enhanced HDS performance especially sulfur resistance may result from the unique core/shell structure of MY(C). The effect of the acid properties and pore structures of the supports on the HDS performances of Pd catalysts was discussed by considering formation of “electronic-deficient” Pd particles and an “auto-regeneration” mechanism involving spillover hydrogen.

Silicotungstic Acid Impregnated MCM-41-like Mesoporous Solid Acid Catalysts for Dehydration of Ethanol

In this study, mesoporous nanocomposite silicotungstic acid (STA) incorporated MCM-41 and mesoporous aluminosilicate catalysts with narrow pore size distributions, in the range of 2.5–3.5 nm, were successfully synthesized following different impregnation procedures. Results showed that the catalyst preparation procedure had significant influence on its activity as well as the product distribution in ethanol dehydration. STAMCM41C catalyst, which was prepared by the impregnation of STA into calcined MCM-41 containing a W/Si ratio of 0.24, and STAMAS catalyst, which was prepared by the impregnation of STA into mesoporous aluminosilicate, showed very high activities in dehydration of ethanol. Ethylene yield showed an increasing trend with temperature, reaching to about 100% above 250 °C. In contrast to ethylene, DEE was formed at lower temperatures, reaching to a yield value of about 70% at 180 °C with STAMCM41C. DEE formation at lower temperatures was concluded to be due to the presence of Bronsted acid sites of this catalyst.

Charge separation in mesoporous aluminosilicates

EPR spectroscopy has been used to investigate spontaneous and/or photo-induced electron transfer between adsorbed organic molecules and the mesoporous aluminosilicate MCM-41 host. Spontaneous electron transfer occurs from the host to electron acceptor molecules with sufficiently favourable reduction potentials (TCNE, TCNQ, 1,4-benzoquinone, 1,4-naphthaquinone and 1,4-anthraquinone), provided the MCM-41 contains aluminium and the radical anion yield correlates with the aluminium content of the host. The semiquinone radical anions are interacting strongly with exposed Al3+ sites, whereas the TCNE and TCNQ radical anions are loosely bound and can be washed from the host. Radical cation formation is observed when electron donor molecules with favourable oxidation potentials are adsorbed in MCM-41 containing aluminium, and the radical cations formed interact with exposed Al3+ sites. This work shows that aluminium-containing MCM-41 contains both electron donating and electron accepting sites which may intervene in intra-molecular charge separation processes in adsorbed organic molecules.

Synthesis and characterization of Cu(I)–salen complex immobilized aluminosilicate MCM-41

Copper(I)–salen: N, N −-ethylenebis(salicylidene-iminato)copper(I), immobilized into the structure of Al-MCM-41 has been synthesized by a liquid-phase adsorption of salen through Cu(I)-exchanged Al-MCM-41 (Cu(I)–salen/M imp) and by a flexible ligand method (Cu(I)–salen/M ss). The ligand and complex were characterized by various physico-chemical measurements such as elemental analysis, powder XRD, mid-spectral FT-IR, thermal analysis (TGA, DTGA), surface texture and scanning electron microscopy (SEM). A comparative in situ FT-IR study of CO adsorption onto simple Cu(I)-exchanged Al-MCM-41 and the complex-immobilized Al-MCM-41 has been carried out. The structure of Al-MCM-41 after modification remains intact, which was evident from XRD and FT-IR studies. The surface characteristics and thermal analysis have provided evidence for successful immobilization of the copper complex inside Al-MCM-41. The structure of Cu(I)–salen complex in Al-MCM-41 prepared by the liquid-phase adsorption of salen was more thermally stable than the analogous prepared by the flexible ligand method. The in situ FT-IR investigation of CO adsorption showed a band at 2124 cm −1 due to Cu(I)–CO in the spectrum of Cu(I)-exchanged Al-MCM-41. This band was shifted to 2146 cm −1 in the spectra of Al-MCM-41-containing complex due to a stronger mode of CO interaction. The Cu(I)–salen/M imp sample was more active than the Cu(I)–salen/M ss one in the generation of CO 2 (2336 cm −1), which was produced from CO and H 2O by the water–gas shift reaction. Surface bound adsorbed species like carbonate (1636, 1590, 1488 and 1434 cm −1) and formate (1727 cm −1) were also detected. The spectrum of the Cu(I)–salen/M ss sample was characterized by a band at 2278 cm −1 assigned to isocyanate ion, NCO −, coordinated to a Cu(I) ion which was absent in the spectra of other samples. The extent of this band depends on the interaction of the immobilized complex with the Al-MCM-41 lattice.

Catalytic conversions of linalool and linalyl acetate over large-pore zeolites and mesoporous MCM-41

The dehydration, condensation, and isomerization of linalool and linalyl acetate occur over the H-and dealuminated forms of zeolites FAU(Y), BEA, MOR, and OFF and mesoporous aluminosilicate MCM-41 at 373–453 K. The yields of linalool isomerization to geraniol and α-and β-terpineols are low. The use of linalyl acetate enhances isomerization; the highest yields of the products of linalyl acetate rearrangement (geranyl acetate and terpinyl acetate) are achieved over DeAlBEA(277). Dehydration produces various C10H16 terpenic hydrocarbon isomers.

Hydrocarbon Reformer Trap by Use of Transition Metal Oxide-Incorporated Beta Zeolites

The concept of a hydrocarbon reformer trap is proposed as a novel technology for cleaning up automobile emissions. Zeolite beta with/without metal species such as iron, manganese, or cobalt is synthesized through a solid phase transformation of mesoporous (metallo)aluminosilicate MCM-41 along with tetraethylammonium cations for structure direction to zeolite beta. The microporosity of zeolite functions as a hydrocarbon trap, and the metal species inside the pores provide a reforming site.

Influence of the Incorporation of Aluminum on the Optical Properties of MCM-41

Different ratios of aluminum were incorporated into MCM-41. PL measurements revealed a blue shift and an enhancement in intensity by 2 orders of magnitude as the Si : Al ratio was decreased to 14. By comparing the PL and the photoluminescence excitation (PLE) spectra of aluminosilicate MCM-41 to silica MCM-41 and to published reports on similar materials, we are able to identify the origin of the photoluminescence enhancement.

Effect of hydrothermal treatment on the structure, stability and acidity of Al containing MCM-41 and MCM-48 synthesised at room temperature

The effect of hydrothermal treatment of the synthesis gel on the structure, hydrothermal and mechanical stabilities and acidity of MCM-41 and MCM-48 aluminosilicates synthesised at room temperature has been investigated by X-ray diffraction, nitrogen adsorption at 77 K and DRIFTS with pyridine as probe molecule. The influence of the Al content and pore size on the structure of the resulting treated Al-MCM-41 materials has also been studied. For all samples improvement of the structural ordering and increase of the pore size, was observed, with pore wall thickness remaining practically unchanged. For Al-MCM-48 an improvement of the pore size uniformity occurs during the treatment. Only a small loss of pore size uniformity occurred for Al-MCM-41 prepared with hexadecyltrimethylammonium bromide, but with samples prepared with tetra and octadecyltrimethylammonium bromide the treatment generated a bimodal pore size distribution. The pore volume increased (17%) in the case of Al-MCM-48 but decreased (5.5–14%) for Al-MCM-41, suggesting a decrease in surface roughness resulting from increase of the degree of condensation of the pore walls. Both treated and untreated samples presented relatively strong Brønsted sites and increase of the Lewis acidity was found to occur upon treatment. Treated samples were found to be more resistant to refluxing in boiling water and mechanical compaction, which was attributed to more polymerised pore walls, with Al-MCM-41 samples tested demonstrating higher stability than Al-MCM-48. However, the differences in stability of samples prepared with or without hydrothermal treatment were not significant. Both treated and untreated samples presented high hydrothermal stability. Although refluxing in boiling water lead to some loss of structural ordering, only a small decrease of pore volume (3–5.5% for Al-MCM-41 and 8-14% for Al-MCM-48) occurred, with practically no alterations in pore size and wall thickness. Ordered mesopore structure, with narrower pores and thicker walls, was still observed after compression at 590 MPa for most of the samples tested.

Synthesis and characterization of novel mesoporous aluminosilicate MCM-41 containing aluminophosphate building units

Novel MCM-41 aluminosilicate/aluminophosphate materials that exhibit good mesostructural ordering have been synthesized and characterised; the synthesis of these silicoaluminophosphates involved the use of gel mixtures containing amorphous mesoporous aluminosilicate and aluminophosphate phases as precursor.