Mesoporous Molecular Sieve Materials Research Articles

From Al-SBA-15 to Ga-SBA-15: Morphology and acidity evolution in the acid-free synthesis

Tuning the morphological and acidic properties of mesoporous molecular sieve materials is highly valuable for catalyst design towards the reactions involving large molecules. In this work, a series of Ga-containing SBA-15 ordered mesoporous materials (OMMs) were synthesized following the acid-free strategy. Ga-SBA-15 exhibits an acid amount of 0.48 mmol/g, comparable to the Al-SBA-15 (0.45 mmol/g). In addition, it is found that the straight short stick particles of Al-SBA-15 integrally bended upon a replacement of Al with Ga and the tendency continuous with the incremental addition of gallium, until fully transforms into the highly dispersed isolated bending particles of Ga-SBA-15. Owing to the improved interparticle-type mesoporosity derived from the dispersed bending particles, the active sites on external surface are highly accessible for large molecules. As for the acidic property, the Brönsted-type acidic property of Al-SBA-15 changed to the Lewis-type acidity with the replacement of gallium. In the Ga-SBA-15 case, more than 93% of strong acid sites were confirmed as Lewis characteristic. On the other hand, Low Density Polyethylene (LDPE) exhibits a faster decomposition rate over Ga-SBA-15 than Al-SBA-15 and Al–Ga bimetallic doped SBA-15 (galloaluminosilicate) catalysts. • Ga-containing SBA-15 mesoporous materials were synthesized following the acid-free strategy. • Replacement of Al with Ga induces a morphological evolution from the straight short stick to a bending shape. • Ga-SBA-15 exhibits strong Lewis acidity and hierarchical pore structure solely composed of interparticle-type mesopores.

Study on SBA-15 as an effective sorbent for dye butyl rhodamine B

Nano mesoporous silica molecular sieve material SBA (Santa Barbara Amorphous)-15 was prepared by hydrothermal method and characterized by means of powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen adsorption-desorption studies. Butyl rhodamine B (BRB) was adsorbed by the SBA-15. The impacts of solution acidity, adsorbent dosage, the initial concentration of butyl rhodamine B, contact time, and temperature on the effects of adsorption were studied and the optimum adsorptive conditions were obtained. The experimental results of adsorption showed that the optimal adsorptive conditions were: pH = 5.0, (SBA-15): BRB = 750: 1, room temperature 30 ± 1 °C and the contact time 20 min. At this time, the adsorption capacity is 1.30 mg/g and the adsorption ratio is 97.52%. Dynamic and thermodynamic properties of the adsorption for butyl rhodamine B by SBA-15 were studied, and the results showed that the adsorption of butyl rhodamine B by SBA-15 is a pseudo-second-order kinetic adsorption. The adsorption thermodynamic data showed that in the 4–30 °C interval ∆G0 0 showed that the adsorption of butyl rhodamine B by SBA-15 is an endothermic process. ΔS0 = 204.9 J / (mol · K) > 0 illustrated that the adsorption process is a reaction of entropy increase. In the 30–60 °C interval, ∆G0 < 0, the reaction can occur spontaneously. ΔH0 = −32.371 kJ/mol < 0 showed that the adsorption of butyl rhodamine B by SBA-15 is an exothermic process. ΔS0 = −30.2 J / (mol · K) < 0 illustrated that the adsorption process is a reaction of entropy decrease. ΔG0 is between −20 and −80 kJ/mol, showing that this adsorption is a coexisting of chemical and physical adsorption. The adsorption of butyl rhodamine B by SBA-15 satisfies the Freundlich adsorption isotherm and belongs to a heterogeneous adsorption.

Ultrastable and strongly acidic Al-SBA-15 with superior activity in LDPE catalytic cracking reaction

Ordered mesoporous molecular sieve materials, Al-SBA-15 was respectively synthesized from the strong acidic and the acid-free media by using a very small quantity of surfactants because of the economic and environmental considerations. The effects of various Al sources on the structural and acidic properties of the final materials were investigated with powder X-ray diffraction (XRD), nitrogen adsorption–desorption at 77 ​K, transmission electron microscopy (TEM), scanning electron microscopy (SEM), inductively coupled plasma (ICP) analyses, and chemical sorption (Py-IR). When following the acid-free strategy, a highly ordered mesostructure can be facilely constructed even with a very low surfactant concentration, extremely regardless of the kind of Al source that used. The resulting Al-SBA-15 exhibited a much higher aluminum content, a stronger acid strength and especially the predominant Brønsted acidic properties in comparison with those synthesized under the traditional strong acidic conditions, thanks to the high-quality crosslinking and self-assembly of silica and alumina species. In addition, the morphology of the product can also be modulated by simply altering the type of aluminum sources. The Al-SBA-15 synthesized with the aluminum nitrate as Al source exhibited very high catalytic activity in the Low Density Polyethylene (LDPE) cracking reaction, and the temperature corresponding to the maximum cracking rate was even comparable to the zeolitic catalyst.

Effect of organic template removal approaches on physiochemical characterization of Ni/Al-SBA-15 and eugenol hydrodeoxygenation

Template removing approaches can significantly impact the physiochemical properties of mesoporous molecular sieve materials. In order to better understand the relationship between template removing approaches and the properties of Ni/Al-SBA-15, four kinds of template removing approaches were introduced to remove the organic template from Al-SBA-15, respectively. The structural characteristics of these materials were analyzed by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray fluorescence (XRF), powder X-ray diffraction (XRD), N2-sorption, Fourier transform infrared spectra (FT-IR), infrared spectra of pyridine adsorption (Py-FTIR), magic angle spinning-nuclear magnetic resonance (MAS-NMR), X-ray photoelectron spectroscopy (XPS) and gas chromatography-mass spectrometry (GC-MS). Ni/Al-SBA-15 of which the organic template was removed by two-step calcination method had the maximum specific surface area (619 ​m2/g). In contrast, Ni/Al-SBA-15 of which the organic template was removed using solvent extraction approaches had the lowest specific surface area (555 ​m2/g). The mesopore diameter of Ni/Al-SBA-15, using electric heating digestion method to remove the template, was significantly increased and the wall thickness was significantly decreased to 11.62 ​nm in comparison with the other samples. The selectivity of products during the process of eugenol hydrodeoxygenation was investigated. High hydrocarbons were obtained during catalytic hydrodeoxygenation over Ni/Al-SBA-15 of which the organic template was removed by using solvent extraction approaches. Compared with direct calcination process, two-step calcination was more effective in removing template and the corresponding catalyst was much more suitable for the hydrodeoxygenation process.

Removal of Pb (II) from Aqueous Medium by Nanostructured Mesoporous Material MCM-48: Studies on Equilibrium, Isotherm, Kinetics and Thermodynamics

Background: In recent years, with the progress of human civilization, environmental pollution is aggravating. Among them, heavy metal pollution is one of the greatest harmful water pollution problems. As a global pollution problem, heavy metal pollution, such as lead, has been given more attention by scientists. How to solve this problem, is an interesting issue. Objective: The aims of the current study are to develop the optimized adsorption conditions of Pb2+ by an MCM (Mobil Composition of Matter)-48 mesoporous molecular sieve material and study the properties of this adsorption. Method: First, an MCM-48 mesoporous molecular sieve was prepared by the hydrothermal method by using cetyltrimethylammonium as the template and tetraethyl orthosilicate as the silica source. The prepared sample was characterized by powder X-ray diffraction and scanning electron microscopy. Then, a harmful heavy metal Pb2+ was adsorbed by MCM-48. Effects of acidity, contact time, temperature, the initial concentration of lead(II) and the dosage of adsorbent on the rates of adsorption were studied, and the optimum adsorptive conditions were obtained. Results: The results show that when pH value was 4.5, the temperature was 18 ± 1°C, contact time was 40 min and m(MCM-48): m(Pb2+) = 2.5 (mass ratio), the adsorptive effect was the best, the adsorption rate was 96.71% and the adsorptive capacity was 386.84 mg/g. After the kinetic calculation, it was known that the process of the adsorption of Pb2+ by MCM-48 conforms to the pseudo-secondorder kinetic equation. Thermodynamic calculation shows that the adsorption is an exothermic process. The adsorption obeys the Freundlich adsorption isotherm equation. Nitric acid, hydrochloric acid and acetic acid were used to study the effects of desorption, indicating that the desorptive effect was the best using 0.1 mol/L of nitric acid as a desorptive agent. At the time of desorption 6 h, its desorptive ratio was the highest and reached 71.11%. Conclusion: This method is an alternative for removing harmful substances containing lead, which has a potential for application in processing lead-polluted waters.

Ruthenium-Based Macromolecules as Potential Catalysts in Homogeneous and Heterogeneous Phases for the Utilization of Carbon Dioxide.

Ruthenium-containing tetraphenylporphyrin (Ru-TPP) molecule was prepared, and the structural elucidation was confirmed using 1H nuclear magnetic resonance (NMR), CHN, and mass spectral analyses. The incorporation of ruthenium ion into the cavities of the macromolecule was confirmed from the disappearance of the 1H NMR signal, characteristic of the N–H bond (−2.72 ppm in TPP). The CHN and mass spectral analyses of the ligand and metallomacromolecules are consistent with the theoretically calculated values. The homogeneous Ru-TPP macromolecule is grafted on the surface of aminosilane-, diaminosilane-, and iodosilane-functionalized SBA-15 molecular sieves. The successful grafting of Ru-TPP on functionalized mesoporous molecular sieve materials was evident from low-angle powder X-ray diffraction, 13C magic angle spinning NMR, and scanning electron microscopy–energy-dispersive X-ray analyses. The resultant homogeneous and heterogenized Ru-TPP catalysts were used for the utilization of carbon dioxide (CO2) under moderate reaction conditions. The homogeneous Ru-TPP catalyst showed first-order kinetics with respect to epoxide with the exclusive formation of cyclic carbonate (about 98%) and an activation energy of 16.07 kg/mol, which is much lower than some of the reported catalysts. Ru-TPP grafted on aminosilane- and iodosilane-functionalized materials showed better catalytic activity (above 90% conversion and 83–96% cyclic carbonate selectivity) and reusability for the chosen reaction.

Vapor phase alkylation of toluene using various alcohols over H3PO4/MCM-41 catalyst: Influence of reaction parameters on Vapor phase alkylation of toluene using various alcohols over H_3PO_4/MCM-41 catalyst: influence of reaction parameters on selectivity and conversion

A mesoporous MCM-41 molecular sieve material with a molar ratio of SiO_2/Al_2O_3 = 70 and loaded with H_3PO_4 was used as a catalyst for the alkylation of toluene, using various alcohols, namely methanol, iso-propanol, and tert-butanol, as alkylating agents. Para-alkylated toluene was the predominant product, formation of which was enhanced by moderate temperature, low amounts of the alkylating agents in the feed, and high carrier gas flow rate. Time on stream was found to exert a profound effect on the selectivity and conversion to the different products.

Study on Several Mesoporous Materials Catalysts Applied to the Removal of Trace Olefins from Aromatics and Commercial Sidestream Tests

Deep removal of trace olefins from aromatics using mesoporous materials and modified mesoporous materials was studied with regard to the removal of trace olefins from aromatic hydrocarbons. The mesoporous materials and the modified mesoporous molecular sieve materials were characterized by X-ray diffraction and Fourier transform infrared (FT-IR) spectroscopy. Under the commercial sidestream test, the effects of four types of mesoporous materials, with regard to the removal of olefins from the aromatics, were evaluated. The result showed that the mesoporous materials that had surface areas larger than 300 m2/g and modified with AlCl3 were best, with regard to the effect on the removal of olefins from aromatics. The FT-IR results showed that the modifier could increase the concentration of weak Lewis acid of mesoporous materials and obviously enhance the effect of removing olefins and prolonging the reaction time.

Optical Spectra of a Novel Polyoxometalate Occluded within Modified MCM‐41.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Optical Spectra of a Novel Polyoxometalate Occluded within Modified MCM-41

The novel polyoxometalate ([(Eu2PW10O38)4(W3O8(H2O)2(OH)4)]22-), also referred to herein as Eu8P4W43, has been immobilized inside the channels of MCM-41 mesoporous molecular sieve material by means of the incipient wetness method. For proper host-guest interaction, amine groups were introduced into the system as a result of an aminosilylation procedure. A stable and integrated Eu8P4W43 polyoxometalate was shown to be formed inside the channels of the modified MCM-41. The products were characterized by XRD, UV-vis absorption, emission, Raman excitation, Raman, and 31P solid-state NMR measurements. Infrared and Raman spectra of the polyoxometalate/MCM-41 composite systems are interpreted as showing spectral shifts due to site induced electrostatic interactions. The photoluminescent behavior of the composite at room temperature indicates a characteristic Eu3+ emission pattern corresponding to 5D0- 7F(J) transitions. A strong photoluminescence suggests the potential utility of the polyoxometalate as a luminescent material.

Aggregation of Thionine within AlMCM-48

We report the formation of aggregated thionine molecules encapsulated within an Al-containing mesoporous molecular sieve material (specifically, AlMCM-48) that possesses a cubic pore structure. XRD, UV−vis absorption, fluorescence, and Raman measurements were used, where appropriate, as spectroscopic tools to characterize the AlMCM-48 host sample and the composite system consisting of the host and encapsulated thionine molecules. Due to the size of the cubic pores possessed by the host, aggregates of thionine larger than the dimers, trimers, and so forth, reported hitherto, are likely formed and are more appropriately termed H-aggregates. The structure of the H-aggregate is proposed. Raman band assignments for thionine are made based on both empirical determinations and quantum chemical calculations using density functional theory at the B3LYP level.

Heterogeneously catalysed partial oxidation of cyclohexane in supercritical carbon dioxide

Heterogeneously catalysed partial oxidation of cyclohexane to cyclohexanol and cyclohexanone in supercritical carbon dioxide was investigated realising batch experiments and continuous runs within the temperature range from 353 to 673 K at pressures between 80 and 160 bar. Before catalytic runs, phase behaviour of the reaction mixture was studied by means of a high-pressure optical cell and the results indicate that: (i) the system is supercritical at the applied reaction conditions; and (ii) results agree well to estimated values using the Peng–Robinson equation of state. Mainly two classes of catalysts were tested in oxidation runs: (i) conventional metal oxide catalysts (active metals Co, Mn, Fe) on alumina or silica as well as microporous (MOR, AlPO-31) and mesoporous materials (Al-MCM-41) as supports; and (ii) organometallic complexes (salenes) of those metals immobilised on mesoporous molecular sieve (MCM-41) or microporous material (EMT). In general, the use of supported metal oxides leads to higher yields for target products cyclohexanone and cyclohexanol compared to the immobilised complexes. Maximum selectivity for these products reached 26% (-one) respective 16% (-ol) at 10% conversion.

Synthesis, characterization, and catalytic properties of chromium-containing hexagonal mesoporous aluminophosphate molecular sieves

Chromium-containing hexagonal mesoporous aluminophosphate molecular sieve materials were synthesized, characterized and evaluated for the oxidation of cyclohexane under mild conditions. The catalysts showed remarkable activity for the chosen reaction with very high substrate conversion and excellent product selectivity. In addition, recycling studies over the spent catalysts as well as studies on quenched solutions under the reaction conditions indicated no or very meager loss in activity; thus, the materials behaved truly as heterogeneous catalysts. This observation was well supported by ICP-AES analysis of the filtrates obtained from the washed catalysts where no leaching of active chromium species was detected. Furthermore, the reaction carried out using these filtrates confirmed the absence of active metal ions as it exhibited only a marginal activity.

Linear combination of XANES for quantitative analysis of Ti–Si binary oxides

A new method is demonstrated for the quantification of Ti-O-Si and Ti-O-Ti bonds in Ti-Si binary oxides. It is based on the linear combination of two reference X-ray absorption near-edge structure (XANES) spectra at the Ti K edge. The proper selection of a Ti-O-Si reference material is most important for the successful application of this method. Three Ti-Si binary oxide systems have been analysed by the new method: Ti-Si mixed oxides, titania supported on silica and Ti-substituted MCM-41 (crystalline mesoporous molecular sieve material invented by Mobil) with various Ti contents.

Investigating the state of Fe and La in MCM-41 mesoporous molecular sieve materials

Fe-containing, La-containing, siliceous and aluminum silicate MCM-41 mesoporous materials were synthesized using water glass as silica source. The states of Fe(III) and La(III) species were investigated by thermogravimetric analysis (TGA), powder X-ray diffraction (XRD), framework infrared (FTIR), electron spin resonance (ESR) and Mössbauer spectroscopic techniques. It was shown that Fe(III) or La(III) species was incorporated into framework. Because the Fe–O or La–O bond is longer than Si–O bond, Fe(III) or La(III) species was limited to insert into framework and transformed from tetrahedrally coordinated state to octahedrally coordinated state upon calcination to remove template.

Studies on the State of Fe and La in MCM-41 Mesoporous Molecular Sieve Materials by TG Analysis and Other Techniques

Siliceous MCM-41 mesoporous materials and those possessing Fe, La, Al,respectively, were synthesized using water glass as silica source. Results from thermogravimetric analysis and other techniques showed us that Fe(III) or La(III) species was incorporated into framework. Owing to Fe–O or La–O bond longer than Si–O bond, Fe(III) or La(III) species was limited to insert into framework and transformed from tetrahedrally coordinated state to octahedrally coordinated state upon calcination to remove template.

Growth of Carbon Nanotubules on Fe/HMS Mesoporous Molecular Sieve Materials

Hexagonal mesoporous molecular sieve materials (HMS) with different pore sizes were applied as supports of Fe-loading catalysts to catalytically synthesize carbon nanotubules. The larger the pore size of HMS is, not only the larger the pore size of the formed carbon nanotubes is, but also the longer the reaction time is. It was observed that the growth of carbon nanotubes can be orientated by the one-dimensional mesoporous structure of HMS.

Effect of Structure and Pore Size of Mesoporous Molecular Sieve Materials on the Growth of Carbon Nanotubes

Microporous and mesoporous molecular sieve materials with different channel structures and pore sizes were applied as supports for Fe-loaded catalysts to catalytically synthesize carbon nanotubes. The deposited carbon materials were characterized by the TEM technique. It was shown that the structures and pore sizes of supports greatly influence the forms and quality of the deposited carbon materials. The larger the pore size of the support used, the larger the diameter and pore size of the carbon nanotubes formed. It seems that the growth of carbon nanotubes can be orientated by the one-dimensional mesoporous structure of hexagonal mesoporous molecular sieve materials.

The very strong photoluminescent (PL) effect of mesoporous molecular sieve materials

MCM-41 mesoporous molecular sieve materials with nanometer-sized pores show the very strong photoluminescent (PL) effect and the Al-depleted defect sites are responsible for this strong PL effect of the investigated MCM-41 samples. The porous channel structures of molecular sieves are another factor influencing the investigated PL effect.

Effect of trivalent elements on the thermal and hydrothermal stability of MCM-41 mesoporous molecular materials

Effect of trivalent elements on the thermal and hydrothermal stability of MCM-41 mesoporous molecular sieve materials has been investigated. Al(III) decreases the thermal and hydrothermal stability of MCM-41 materials, whereas La(III) and Fe(III), especially Fe(III), can improve the thermal and hydrothermal stability. Benzene adsorption and IR spectra suggested that thick channel wall and the fewer structural defect sites in MCM-41 would enhance the thermal and hydrothermal stability of MCM-41.