Mesoporous Molecular Sieve MCM-41 Research Articles

Photophysical and photochemical properties of Coumarin-6 molecules incorporated within MCM-48

Laser dye Coumarin-6 (C6) molecules were incorporated into the three-dimensional channels of mesoporous molecular sieve MCM-48. The photophysical and photochemical properties of C6 in MCM-48 were characterized by absorption, emission and electron paramagnetic resonance (EPR) spectra. The results indicated that MCM-48 exerted a significant influence on the photophysical and photochemical properties of the incorporated C6 molecules. Absorption maxima of C6 in MCM-48 exhibited large red-shift while emission exhibited relatively small red-shift compared with those in ethanol. A broad EPR signal with a g value of 2.003 indicates that electron transfer occur easily in the C6/MCM-48 composite.

MCM-41 anchored Schrock catalyst Mo( [dbnd]CHCMe 2Ph)( [dbnd]N-2,6- i-Pr 2C 6H 3)[OCMe(CF 3) 2] 2-activity in 1-heptene metathesis and cross-metathesis reactions

Schrock carbene complex Mo( CHCMe 2Ph)( N-2,6- i-Pr 2C 6H 3)[OCMe(CF 3) 2] 2 was immobilized on mesoporous molecular sieves MCM-41 via a ligand exchange reaction with OH surface groups. The heterogeneous catalyst prepared in this way was Mo-leaching resistant and exhibited high activity and selectivity in metathesis of neat 1-heptene. The catalyst activity in cross-metathesis of 1-heptene with norbornene and cyclooctene was also studied.

Progress in Pore‐Size Control of Mesoporous MCM‐41 Molecular Sieve Using Surfactant Having Different Alkyl Chain Lengths and Various Organic Auxiliary Chemicals

AbstractFor Abstract see ChemInform Abstract in Full Text.

Metal cation sensing material based on the assembly of meso-terakis(4-N,N,N-trimethylamiophenyl) porphyrin and mesoporous molecular sieve MCM-41

The metal cation sensing material was prepared by entrapment of a water-soluble porphyrin compound, meso-terakis(4-N,N,N-trimethylamiophenyl) porphyrin (TTMAPP), in mesoporous molecular sieve MCM-41. The powder X-ray diffraction (XRD) spectra results demonstrated that after the introduction of TTMAPP, the ordered channel arrangement of MCM-41 remained. The assembly material, TTMAPP/ MCM-41, exhibited a typical absorption feature of porphyrin compound. Emission spectrum study revealed that the introduction of zinc (II) cation resulted in the formation of a new emission peak at 600 nm for TTMAPP/MCM-41, while the presence of copper (II) cation at low concentration led to that the luminescent intensity of TTMAPP/MCM-41 was obviously reduced by 68.42%. The experiment results demonstrated that TTMAPP/MCM-41 is a cation sensing materials with good performance.

11C-radioisotope labeled methanol conversion over H- and Cs- modified ZSM-5, Beta zeolites and MCM-41 mesoporous molecular sieve

The Na–MCM-41 mesoporous molecular sieve, Na–ZSM-5 and Na–Beta zeolites have been modified by Cs- and H- using ion-exchange method and characterized by XRD, SEM and nitrogen adsorption. The conversion of methanol was studied over H- and Cs- modified ZSM-5, Beta zeolites and MCM-41 mesoporous molecular sieve. Methanol was in 11C-radioisotope labeled form in-order to follow its conversion during the catalytic process, since the radioactivity method provides a very sensitive detection possibility to investigate the conversion of small amounts of methanol and some intermediates at different reaction times and temperatures. The understanding of reaction mechanism is important for side-chain methylation over Cs–zeolite catalysts by methanol, as they are more selective than other alkali exchanged zeolites (Li, Na and K). The reaction pathway of the transformation of methanol to hydrocarbons and aldehydes has been elaborated.

Oxidation of Cyclohexane over Bi-incorporated MCM-41 Mesoporous Molecular Sieve Catalyst with Oxygen as Oxidant

Abstract Bismuth-incorporated MCM-41, which was directly synthesized under strongly acidic conditions and characterized, for the first time, by XRD, UV–vis and Raman spectroscopy, was used as catalyst for the oxidation of cyclohexane without organic solvent using O2 as oxidant, and the results of reaction indicate that Bi-MCM-41 is a very stable and efficient catalyst.

Physical chemistry of nanostructured molecular sieves by the study of phase diagrams: the case of the cetyltrimethylammonium bromide–tetramethylammonium silicate–water system

A phase diagram for the system cetyltrimethylammonium bromide (CTAB)/tetramethylammonium silicate (TMASi)/water has been constructed in order to better understand the interactions between these precursors of the MCM-41 mesoporous molecular sieves. Three different CTAB concentration regions were analyzed: the dilute and semidilute regions, where simple surfactant species, such as monomers and spherical and nonspherical CTAB micelles, are found, and the concentrated region, involving liquid-crystalline phases. In the dilute and semidilute regions, the formation of a white nanostructured solid, having a hexagonal array similar to that found in MCM-41 materials, was observed. Precipitation of this solid requires some degree of surfactant monomer aggregation, which is favored by the presence of silicate anions. If micelles have already been formed, the material can be obtained at any CTAB concentration above a threshold concentration of silicate anions. These facts suggest that silicate anions have an important role in changing the aggregation and/or the shape of the surfactant aggregates. In the concentrated region, precipitation of the solid was not observed, but the presence of the silicate anions alter the characteristics of the liquid-crystalline phase formed by the surfactant. The system shows very complex and rich behavior and its investigation may be very useful in understanding the processes of nanostructured solid formation.

Synthesis and characterization of Mn–MCM-41and Zr–Mn-MCM-41

Mesoporous silica molecular sieves MCM-41 containing zirconium and manganese ions (Zr–Mn-MCM-41) with Si/(Zr+Mn) ratio equal to 49, 98, 147, 196, 262 and 327 and only manganese ions with Si/Mn ratio equal to 15, 31, 46, 61, 82 and 102 respectively, were synthesized under hydrothermal conditions using cetyltrimethylammonium (CTMA +) surfactants as template in the absence of auxiliary organics. The mesoporous materials, viz. Zr–Mn-MCM-41 and Mn-MCM-41 were characterized using several techniques, e.g. ICP-AES, XRD, FTIR, Nitrogen adsorption, TG/DTA, ESR, UV–Vis/DRS, SEM and TEM. ICP-AES studies indicated the content of zirconium and manganese in the mesoporous materials. XRD studies indicated that the materials had the standard MCM-41 structure. FTIR studies showed that zirconium and manganese ions were incorporated into the hexagonal mesoporous structure of Zr–Mn-MCM-41 and Mn-MCM-41. The thermal stability of the as-synthesized materials was studied using TG/DTA. Nitrogen adsorption was used to determine specific surface area, pore diameter, pore volume and wall thickness in the calcined Zr–Mn-MCM-41 and Mn-MCM-41 mesoporous molecular sieves. The incorporated of zirconium and manganese ions oxidation state was determined by ESR and UV–Vis/DRS. The morphology of Zr–Mn-MCM-41 and Mn-MCM-41 materials was determined by SEM. The inference that the Zr–Mn-MCM-41 and Mn-MCM-41 mesoporous materials had uniform pore size was obtained by TEM studies. The incorporated metal ions as Zr 4+, Mn 2+ and Mn 3+ in Zr–Mn-MCM-41 are coordinated to Si(IV) by tetrahedral, disordered octahedral and tetrahedral environments respectively. The zirconium and manganese ions are homogenously dispersed on the inside silica surface of the Zr–Mn-MCM-41, but only the manganese ion is not homogenously dispersed on the inside surface of the Mn-MCM-41 under hydrothermal conditions. Thus the Zr–Mn-MCM-41 mesoporous molecular sieves are more useful for oxidation of olefin reaction with TBHP, e.g., in the epoxidation of trans-stilbene, trans-stilbene-oxide (84.58%) was found to be the highest in the presence of Zr–Mn-MCM-41(49).

Synthesis, characterization, and catalytic properties of stable mesoporous molecular sieve MCM-41 prepared from zeolite mordenite

Mesoporous molecular sieves (denoted as M-MCM-41) with ordered hexagonal structure have been successfully synthesized from the assembly of precursors from preformed zeolite Mordenite with CTAB surfactant micelle in alkaline media. The samples were characterized by XRD, N 2 adsorption, IR and DTG. The materials exhibit highly hydrothermal stability, as compared with conventional MCM-41. Characterization results indicate that the mesoporous walls of M-MCM-41 contain the secondary building units similar to those in microporous crystal of zeolite Mordenite. In catalytic dealkylation of C10 + aromatic hydrocarbon, M-MCM-41 shows higher activities in comparison with Mordenite and MCM-41, which would be ascribed to the combination of advantages of both MCM-41 (large pores) and Mordenite (strong acidity). Furthermore, this synthesis strategy could be used as a new general method for the preparation of hydrothermally stable mesoporous aluminosilicate materials under alkaline conditions.

Preparation and catalytic application of MCM-41 modified with a ferrocene carboxyphosphine and a ruthenium complex

Abstract Reaction of 1′-(diphenylphosphino)ferrocenecarboxylic acid (Hdpf) with mesoporous molecular sieve MCM-41 gives immobilized carboxyphosphine (3), which was further reacted with [{Ru(η6-p-cymene)Cl(μ-Cl)}2] (1) to afford Ru/carboxyphosphine-modified molecular sieve 4. A simple reaction between MCM-41 and 1 afforded Ru-only modified molecular sieve 5. Materials 4 and 5 were tested as catalysts for the reaction of propargyl alcohol with benzoic acid to give 2-oxopropyl benzoate (6). The reactions catalyzed with immobilized catalysts are slower and give lower yields of the ester as compared to the homogeneous precatalyst [Ru(η6-p-cymene)(Hdpf-κP)Cl2] (2), which was prepared from Hdpf and the dimer 1. Formation of ester 6 catalyzed with 4 and 5 competes with a parallel, propargyl alcohol consuming process, which occurs also with MCM-41 itself in the absence of benzoic acid and ruthenium compounds. The solid-state structure of 2·CH2Cl2 has been determined by single-crystal X-ray diffraction.

Preparation of organic–inorganic material from MCM-48 and pyrylium salt

Pyrylium salt 2,4-diphenyl-5,6,7,8-tetrahydro-chromenylium; perchlorate (S-2) was introduced into the three-dimensional channels of mesoporous molecular sieve MCM-48 by post-synthesis impregnation method. There were large blue shifts in absorption and fluorescence spectra when S-2 was included into MCM-48. The results indicate that the S-2 molecules exist in the monomer state in MCM-48 and form hydrogen bond with the surface silanols of MCM-48.

Transition Metal Modified TiO2-Loaded MCM-41 Catalysts for Visible- and UV-Light Driven Photodegradation of Aqueous Organic Pollutants

A number of transition metal (Cr, V, Fe, Cu, Mn, Co, Ni, Mo, and La) incorporated MCM-41 mesoporous molecular sieves with Si/Me = 80 have been synthesized by a hydrothermal method. It was demonstrated that the presence of transition metal salts in the gel during synthesis hinders the action of the template, which results in pores of MCM-41 that are not well-formed. These materials were then loaded with TiO2 via the sol−gel method, and the resulting materials were explored for the destruction of 4-chlorophenol in the presence of visible, as well as UV, light. A combination of various physicochemical techniques such as N2 physisorption, O2 chemisorption, X-ray diffraction (XRD), diffuse reflectance UV−vis (DR UV−vis), and temperature program reduction (TPR) were used to characterize the chemical environment of these transition metals in the prepared catalysts. The dispersion of transition metals as determined by O2 chemisorption suggests that they are well dispersed inside the MCM-41 framework, but the disp...

Synthesis of Novel Ag Modified MCM-41 Mesoporous Molecular Sieve and Beta Zeolite Catalysts for Ozone Decomposition at Ambient Temperature

Mesoporous molecular sieve Na-MCM-41 with Si/Al ratio 20 and 50 and Na-beta zeolite with Si/Al ratio 11 were synthesized and characterized using X-ray powder diffraction, scanning electron microscope and nitrogen adsorption. The Ag (5 and 2 wt%) modifications of H-MCM-41-20, H-MCM-41-50 and H-beta-11 catalysts were carried out using impregnation method. The catalysts were tested in the decomposition of ozone at ambient temperature. The 5 wt% Ag-H-MCM-41 catalyst showed a very high decomposition of ozone (~98%). The 5 wt% Ag-H-MCM-41-50 catalyst exhibited higher decomposition rate than 2 wt% Ag-H-MCM-41-50. The Ag modified H-MCM-41 catalyst with higher Si/Al ratio showed higher reaction rate than the catalyst with lower Si/Al ratio. The H-MCM-41 catalyst without Ag exhibited the lowest decomposition of ozone indicating an important role of Ag in the reaction.

Comparison of mesoporous solid acid catalysts in the production of DABCO by cyclization of ethanolamineI. Synthesis and characterization of mesoporous solid acid catalysts

Mesoporous silica molecular sieves MCM-41 containing zinc and aluminum ions (Zn–Al-MCM-41) with Si/(Zn + Al) ratio equal to 75, 151, 228, 304 and 380 and only aluminum ions (Al-MCM-41) with Si/Al ratio equal to 21, 42, 62, 83 and 104 respectively, were synthesized under hydrothermal conditions using cetyltrimethylammonium (CTMA+) surfactants as template in the absence of auxiliary organics. The mesoporous materials viz. Zn–Al-MCM-41 and Al-MCM-41 were characterized using several techniques. e.g. ICP-AES, XRD, FTIR, TG/DTA, Nitrogen adsorption, 27Al-MAS-NMR, SEM, TEM, XPS and pyridine acidity (TPD and FTIR) measurements. The d-spacing value and unitcell parameter in the Zn–Al-MCM-41 and Al-MCM-41 decreases by increasing the metal ions content. FT-IR studies showed that zinc ion was incorporated into the hexagonal mesoporous Al-MCM-41 materials, however, the wavenumber of the anti-symmetric Si–O–Si vibration bands (1096 cm−1) in Zn–Al-MCM-41 are higher than those in Al-MCM-41 (1083 cm−1). These bands should be due to the increase of the mean Si–O distance in the wall caused by the substitution of the small ionic radii of silicon by the larger ionic radii of zinc. The surface area, pore diameter, pore volume of Zn–Al-MCM-41 is smaller than that of Al-MCM-41 while the hydrothermal stability and acid sites in the Zn–Al-MCM-41 are higher than that of Al-MCM-41 due to increasing protons with the aluminum ions non-framework by the introduction of zinc ions. Thus Bronsted and Lewis acid sites in Zn–Al-MCM-41 are same, but its acid sites are higher than Al-MCM-41.

Comparison of mesoporous solid acid catalysts in the production of DABCO by cyclization of ethanolamine: I. Synthesis and characterization of mesoporous solid acid catalysts

Mesoporous silica molecular sieves MCM-41 containing zinc and aluminum ions (Zn–Al-MCM-41) with Si/(Zn + Al) ratio equal to 75, 151, 228, 304 and 380 and only aluminum ions (Al-MCM-41) with Si/Al ratio equal to 21, 42, 62, 83 and 104 respectively, were synthesized under hydrothermal conditions using cetyltrimethylammonium (CTMA +) surfactants as template in the absence of auxiliary organics. The mesoporous materials viz. Zn–Al-MCM-41 and Al-MCM-41 were characterized using several techniques. e.g. ICP-AES, XRD, FTIR, TG/DTA, Nitrogen adsorption, 27Al-MAS-NMR, SEM, TEM, XPS and pyridine acidity (TPD and FTIR) measurements. The d-spacing value and unitcell parameter in the Zn–Al-MCM-41 and Al-MCM-41 decreases by increasing the metal ions content. FT-IR studies showed that zinc ion was incorporated into the hexagonal mesoporous Al-MCM-41 materials, however, the wavenumber of the anti-symmetric Si–O–Si vibration bands (1096 cm −1) in Zn–Al-MCM-41 are higher than those in Al-MCM-41 (1083 cm −1). These bands should be due to the increase of the mean Si–O distance in the wall caused by the substitution of the small ionic radii of silicon by the larger ionic radii of zinc. The surface area, pore diameter, pore volume of Zn–Al-MCM-41 is smaller than that of Al-MCM-41 while the hydrothermal stability and acid sites in the Zn–Al-MCM-41 are higher than that of Al-MCM-41 due to increasing protons with the aluminum ions non-framework by the introduction of zinc ions. Thus Bronsted and Lewis acid sites in Zn–Al-MCM-41 are same, but its acid sites are higher than Al-MCM-41.

Tertiary amino group covalently bonded to MCM-41 silica as heterogeneous catalyst for the continuous synthesis of dimethyl carbonate from methanol and ethylene carbonate

A tertiary amino group was covalently bonded to the silica surface of mesoporous MCM-41 molecular sieve. The resulting anchored complex was characterized by X-ray powder diffraction (XRD), nitrogen adsorption and FT-IR spectroscopy, and was used as catalyst for the transesterification of ethylene carbonate and methanol to produce dimethyl carbonate. The catalyst exhibits excellent stability as well as good catalytic activity in the reaction conditions, and was subjected to utilization for 100 h without obvious loss of activity.

Cu state and behaviour in MCM-41 mesoporous molecular sieves modified with copper during the synthesis––comparison with copper exchanged materials

CuAlMCM-41 and CuNbMCM-41 mesoporous molecular sieves with various Si/Cu ratios were synthesised at room temperature (RT) by the method of direct insertion of metal ions during the synthesis. The physicochemical properties of the materials have been investigated by means of XRD, N 2 adsorption/desorption, 27Al MAS NMR and 29Si MAS NMR, ESR, H 2-TPR and FTIR combined with NO or NO + NO 2 adsorption. It has been documented that H 2-TPR measurements and FTIR spectroscopic study combined with the adsorption of NO and NO + NO 2 are useful methods for the estimation of the localisation of transition metal cations (framework or extra-framework positions). The comparison of results obtained for CuMCM-41 catalysts prepared by the direct synthesis with those for copper-exchanged MCM-41 allows the statement that copper in CuMCM-41 exhibits a different state and behaviour than that in Cu-MCM-41. It could suggest that copper in CuMCM-41 materials is partially located in the skeleton. The catalytic activity was tested in the liquid phase hydroxylation of phenol. CuNbMCM-41 material presents the highest yield of hydroquinone, that is why this catalyst can be attractive material for hydroxylation with selectivity to p-product. The role of copper leaching during the liquid phase reaction in water medium is pointed out.

Incorporation of aluminum into the framework of mesoporous MCM-41: the contribution of diffuse reflectance spectroscopy

Diffuse reflectance spectroscopy (DRS) has been used to investigate structural modification of aluminum-incorporated mesoporous molecular sieves MCM-41. A room temperature synthesis method was used for preparation of pure silica MCM-41 and for aluminum-containing AlMCM-41 materials. Samples with Si/Al ratios of 100, 50, 25 and 10 were synthesized. A post-synthesis modification of a purely siliceous MCM-41 was also carried out using an aqueous aluminum sulfate solution with appropriate concentration to obtain materials with the same Si/Al ratios. The products possess highly ordered structure and high surface area as evidenced from X-ray diffraction (XRD) and BET measurements, respectively. DR spectra of aluminum-containing materials show a distinct and well-defined band at ≈200 nm correlated to framework aluminum. The intensity of this band is proportional to the amount of aluminum incorporated. post-synthesis-modified materials show a slightly lower incorporation of aluminum according to the DR spectra and energy-dispersive X-ray (EDX) analysis. Reflectance spectra of the as-synthesized samples, irrespective of the preparation method, show no significant amount of extra-framework aluminum. A very small amount of extra-framework aluminum was found when samples with a low Si/Al were calcined. These species are detected by producing a broad band at about 240–280 nm in the DR spectra.

Nickel containing MCM-41 and AlMCM-41 mesoporous molecular sieves: Characteristics and activity in the hydrogenation of benzene

Pure siliceous and aluminosilicate mesoporous molecular sieves of MCM-41 type have been used as matrices for nickel incorporation (1.7–5%, w/w) via wet impregnation. Moreover, the AlMCM-41-32 material was modified by the cation-exchange method. The properties of the prepared catalysts were studied by means of XRD, XPS, N 2-adsorption, H 2-TPR, H 2-adsorption and TPD. The reaction of gas-phase benzene hydrogenation was carried out on the prepared catalysts. The hydrogen spillover effect in this reaction was also studied using 3% Ni/MCM-41 and 3% Ni/AlMCM-41-32 catalysts diluted by MCM-41 and AlMCM-41-32, respectively. NiSiO 3 and Ni 2O 3 species in the calcined precursor were shown by H 2-TPR and XPS techniques. The presence of metallic aluminium is shown in the Ni/AlMCM-41-32 reduced materials. The reducibility of the catalyst is strongly influenced by the nature of the matrix and the method of preparation. The kinetic study of benzene hydrogenation on 1.7% Ni catalysts demonstrated various partial orders in hydrogen and benzene ascribed to the existence of several surface chemical processes. Investigations on the hydrogen spillover effect showed a maximum of activity for the diluted catalyst. The intensity of hydrogen spillover is strongly decreased in the presence of Al. The kinetic study with the mechanical mixtures suggested changes in the surface reactions due to the contribution of the support to the chemical processes. Moreover, the results strongly indicated that the migration of hydrogen atoms from the metal phase onto the support oxide is assisted by the aromatic hydrocarbon.

Adsorption of Lysozyme over Mesoporous Molecular Sieves MCM-41 and SBA-15: Influence of pH and Aluminum Incorporation

The adsorption of lysozyme on the mesoporous molecular sieves MCM-41 and SBA-15 from buffered solutions with different pH values has been studied as a model protein adsorption system. The amount adsorbed depends on the solution pH as well as on the pore volume and the composition of the adsorbent. The adsorption isotherms at pH 6.5 to 10.5 fitted the Langmuir model (type L isotherm), while the isotherms recorded at pH 12 are of the S type. The maximum amount adsorbed was observed for AlSBA-15 at pH 9.6 and amounted to 47.2 μmol/g (580 mg/g). The stability of SBA-15 toward to the buffer solution is higher for SBA-15 as compared to MCM-41, which is probably a consequence of the higher wall thickness of the former material. Diffuse reflectance Fourier transform infrared spectra of the adsorbed lysozyme confirm that the adsorption of the enzyme did not result in denaturation of Lz.