Synthesis Of MCM-41 Research Articles

Preparation, characterization and application of the magadiite based mesoporous composite material of catalytic interest

The synthesis of a new type of mesoporous materials by intercalation of silica between magadiite layers was carried out. For the preparation of the composite material, reactive silica gels with compositions characteristic for the synthesis of MCM-41 were used. Samples synthesized with various compositions were characterized by X-ray diffraction, IR and NMR spectroscopy, thermal analysis, BET measurements as well as scanning and transmission electron microscopy. These techniques showed that the composite samples are ordered materials with a pore opening around 4 nm, a specific surface area over 700 m 2 g −1, a regular pillared structure and tetrahedrally coordinated aluminum in the silica walls. The acidity of the samples, determined by the adsorption of pyridine and monitored by IR spectroscopy, was negligible for pure silica composites, while significant Brønsted and Lewis acid sites in different concentrations were found for the aluminum-containing materials. The catalytic activity of the samples followed the same trend in acid-catalyzed double bond isomerization of 1-butene to 2-butenes and in the alkylation of toluene with benzyl chloride. Physisorption of benzene and chemisorption of methanol were concluded from in situ adsorption measurements by IR spectroscopy. The thermal and mechanical stabilities of the composite materials were higher than those of the MCM-41, irrespective of the composition.

Synthesis of MCM-48 under low surfactant/silicon molar ratio conditions

Synthesis of MCM-48 under low surfactant/silicon molar ratio conditions

Synthesis, characterization and photocatalytic properties of titania-modified mesoporous silicate MCM-41

A series of titania modified mesoporous silicate MCM-41 (MCM-TiO2) samples with variable Ti/Si ratios have been synthesized from tetrabutyltitanate and calcined MCM-41. The samples were characterized by powder X-ray diffraction (XRD), FTIR spectroscopy, thermal analysis (DTA–TG), nitrogen adsorption–desorption at 77 K, transmission electron microscopy (TEM), and solid state diffuse reflectance UV–VIS spectroscopy. It was found that tetrabutyltitanate cocondensation occurred with pendant OH groups of MCM-41 leading to Si–O–Ti bonds so modifying the inner pore surface of MCM-41 after hydrolysis and calcination. In the titania modified MCM-41 samples, although titania species were in tetrahedral rather than octahedral coordination which is predominant in crystalline titania, it still exhibited good photocatalytic activity for oxidizing phenol to carbon dioxide and water.

New mineralization agents for the synthesis of MCM-41

Silicate and aluminosilicate MCM-41 molecular sieves have been synthesized in the presence of various new mineralization agents, such as methylamine, dimethylamine, ethylamine and diethylamine. The products were characterized with a series of techniques. XRD, TEM and nitrogen adsorption-desorption measurements suggest that the products possess highly ordered structures. 29Si NMR results show that the resultant mesophase frameworks are condensed with a higher degree than those of products prepared with NaOH as the mineralization agent. These alkali-metal-free synthesis media offer a simple and effective method for the direct preparation of high quality H-type aluminosilicate MCM-41, as shown by XRD, 27Al NMR and NH 3 TPD results. Both the pure silica and the aluminum-containing samples exhibit excellent thermal (in air up to 1373 K) and hydrothermal stability (in hot water of 353 K, 48 h for the former and 72 h for the later). The formation of the high quality MCM-41 material is discussed in terms of a buffer effect of the synthesis media, which is due to the presence of the new mineralization agents. The evidence was obtained by monitoring the pH values of the synthesis.

Novel route in the synthesis of MCM-41 containing framework aluminum and its characterization

Mesoporous molecular sieve MCM-41 with incorporated structural aluminum (Al-MCM-41) was prepared by hydrolysis of a solution of tetraethoxysilane and aluminum isopropoxide in the presence of ammonia as a catalyst. This method provides Al-MCM-41 of different Si/Al ratios from 13 to 297 corresponding to 0.3–7 mol% Al within an hour. X-ray diffraction and nitrogen adsorption measurements showed that the Al-MCM-41 prepared by this method had a highly ordered structure of pore arrays. Most Al atoms in these samples were incorporated tetrahedrally in the MCM-41 structure, which gave rise to cationic sites in the framework.

Mechanical Stability of Mesoporous Molecular Sieve MCM-48 Studied by Adsorption of Benzene, n-Heptane, and Cyclohexane

The synthesis of MCM-48 has been performed in a 5 L autoclave, and the progress of the synthesis has been monitored by X-ray powder diffraction and 29Si MAS NMR. The formation of MCM-48 progresses via an intermediate phase, whose conversion into the cubic phase is triggered by condensation of the silanol groups. The mechanical stability of silica mesoporous material MCM-48 has been investigated employing powder X-ray diffraction, nitrogen adsorption, and subcritical organic vapor (benzene, n-heptane, and cyclohexane) adsorption isotherms and breakthrough curves. The adsorption capacity is affected considerably by mechanical compression between 20 and 400 N mm-2, while the material is destroyed to a large extend at 480 and 600 N mm-2, which is reflected by a dramatic decrease in adsorption capacity and poor X-ray diffraction patterns. As a result of its three-dimensional structure, the mechanical stability of MCM-48 is larger compared to that of MCM-41 but still low compared to that of crystalline structur...

Expanding the Pore Size of MCM-41 Silicas: Use of Amines as Expanders in Direct Synthesis and Postsynthesis Procedures

New opportunities are discussed for the pore-size engineering of mesoporous silicas using amines as swelling agents. It was shown that N,N-dimethylhexadecylamine (DMHA) is a convenient expander allowing for the synthesis of large-pore MCM-41 in mild conditions. Their pore size increased and the structural ordering decreased as the amount of the amine in the synthesis gel increased. The material with the largest pore size attained (7.7 nm) exhibited narrow pore-size distribution, very large primary mesopore volume, but a disordered pore system. Other amines, such as trioctylamine and tridodecylamine, were also found to be suitable for preparation of large-pore MCM-41 but not as efficient as DMHA. Addition of dimethyldecylamine (DMDA), dimethyloctylamine (DMOA), and small trialkylamines to the synthesis gel did not lead to the pore size enlargement but decreased the structural uniformity and in some cases resulted in development of microporosity. It was also demonstrated that it is possible to induce up to ...

A comparison of post-synthesis alumination and sol-gel synthesis of MCM-41 with high framework aluminum content

Abstract Aluminum-containing mesoporous MCM-41 materials were prepared by post-synthesis modification of a purely siliceous MCM-41 using different Al sources: AlCl3, aluminum isopropoxide and NaAlO2. The structure, thermal stability and acidity of these materials have been investigated and compared with Al-MCM-41 prepared by direct hydrothermal synthesis. Irrespective of the preparation method, the surface area, pore diameter, crystallinity and thermal stability of Al-MCM-41 decrease with increasing Al content. Post-synthesis modified materials possess better thermal stability, and this method allows for the incorporation of more aluminum without disintegration of the mesoporous structure as compared to Al-MCM-41 prepared by direct hydrothermal synthesis. The post-synthesized Al-MCM-41 has a moderate acidity, comparable to that of the direct hydrothermally-synthesized material.

The effect of alkan-1-ols addition on the structural ordering and morphology of mesoporous silicate MCM-41

The effects of adding alkan-1-ols to surfactant-silicate gels during the synthesis of mesoporous silica MCM-41 are reported. Upon adding an optimal amount of medium carbon chain length alkan-1-ols (C m H 2m+1 OH, C m OH; m≥4) to quaternary ammonium halides C n H 2n+1 TMAX (n=10-14, C n TMAX, X=Br or Cl)-silicate systems, a marked improvement in the hexagonal order and the morphology of the synthesized MCM-41 materials was found. The optimal amount of added C m H 2m+1 OH for the formation of well ordered hexagonal structure was found to decrease with increasing carbon chain length of the C n H 2n+1 TMAX surfactant and C m H 2m+1 OH. However, when an excessive amount of alcohol is added, the mesostructure obtained from the longer carbon chain length C n H 2n+1 TMAX-silicate (n≥12) systems becomes lamellar. The addition of C m OH (m≥4) offers a new synthetic approach to form lamellar-hexagonal liquid crystal intermediates necessary for synthesizing tubules-within-tubule (TWT) hierarchical structures whose morphology and size can be controlled by varying the water content and the C m H 2m+1 OH/surfactant ratio.

A method for the synthesis of high quality large crystal MCM-41

Preparation of large crystal MCM-41 has been achieved by using calcined small crystallite MCM-41 as seeds in a multistage synthesis method. The possible formation mechanism is discussed. We believe that the newly discovered method is particularly important in making high quality thin films of mesoporous materials.

Mesoporous materials synthesized by intercalation of silicate tubes between magadiite layers

Synthesis of mesoporous material by pillaring of magadiite with silica was investigated. For pillaring reactive silica gel with composition characteristic for the synthesis of MCM-41 was used. The composite samples were characterized by XRD, SEM, TG-DTA, IR and BET methods. Increased mechanical stability of the composite was proven. The acidity of surface OH groups were studied by adsorption of pyridine monitored by IR spectroscopy. The results revealed the presence of both Brønsted and Lewis acid sites on the aluminium containing composite.

Synthesis of High-Quality MCM-48 and MCM-41 by Means of the GEMINI Surfactant Method

Pure silica MCM-48 and MCM-41 materials were prepared using GEMINI surfactants, with the general formula [CnH2n+1N+(CH3)2−(CH2)s−N+(CH3)2CmH2m+1].2Br-, abbreviated as GEM n-s-m. The alkyl chain length (n,m) determines the pore size, whereas the length of the spacer (s) influences the crystallographic phase formed. A spacer length of 10−12 C yields the cubic MCM-48; smaller spacers favor the hexagonal MCM-41 phase. A hydrothermal treatment is introduced as an intermediate synthesis step, which strongly improves the quality and stability of the calcined materials. The hydrothermal treatment reduces the synthesis time of high-quality MCM-48 to only 2 days. Both GEM 18-12-18 and GEM 16-12-16 yield excellent MCM-48, with a surface area in the range 1200−1600 m2/g and pore volumes exceeding 1.2 mL/g. The maxima of the very narrow pore size distributions are found at rp = 13.1 and 12.2 Å, respectively. The GEM 16-10-16 and GEM 18-10-18 surfactants also yield MCM-48, but the quality of these materials is lower. The GEM 16-8-16 finally yields MCM-41.

Synthesis of MCM-41 using microwave heating with ethylene glycol

Mesoporous material MCM-41 with hexagonal arrangement is obtained by microwave treatment of precursor gel at 100–120°C for 1 h or less, a very short period of time compared with the hydrothermal method. In addition to shorter synthesis time, microwave radiation in the synthesis of MCM-41 provides a way to control its crystallinity and morphology. Especially the addition of small amount of ethylene glycol (EG) in synthetic mixture contributes to improving crystallinity, forming homogeneous particle shape and reducing particle size of MCM-41 under microwave radiation. Attenuated total reflectance (ATR)/FTIR and photoluminescence (PL) spectroscopy have been used to monitor intermediate step of microwave preparation of MCM-41.

Liquid-phase oxidation of cyclohexane using Co-P-MCM-41 catalyst

Co-P-MCM-41 catalyst was prepared by introduction of cobalt nitrate and phosphoric acid during gel-preparation for the synthesis of MCM-41. The catalyst, which was found to have very high surface area (995 m2/g), was tested for the one step liquid oxidation of cyclohexane to adipic acid using a semi-batch autoclave reactor (without addition of any promoter and solvent) at 115°C and in a flow of 5 bar of oxygen. The effect of the amount of catalyst on the induction time, catalytic conversion of cyclohexane, and selectivity to adipic acid was investigated. Depending on the amount of catalysts used in the reaction (from 0.1 to 3.0 g), an induction period from about 100 min to less than 10 min, cyclohexane conversion from 30 to 99%, and a selectivity to adipic acid from 15 to 40 %, could be achieved using Co-P-MCM-41 as the catalyst.

Synthesis and characterisation of titanium-containing MCM-41 using (NH4)3[Ti(O2)F5] as the titanium source

Titanium-containing MCM-41 materials were synthesised using triammonium pentafluoroperoxotitanate (NH4)3[Ti(O2)F5] as the titanium source, using several templates, varying in chain length and additional auxiliary organic agents in order to vary the mean pore size. The materials obtained were characterised with XRD, UV/Vis, nitrogen adsorption and desorption, DRIFT, ICP–AES and thermogravimetric analysis. In all materials the titanium was present as tetrahedrally coordinated Ti(IV). The pore size was dependent on the surfactant chain length. The addition of an auxiliary organic compound had only minor influence on the pore size. The use of the BJH equation for the determination of the pore size distribution can result in pore sizes that are too small.

Synthesis of MCM-48 Using Mixed Cationic−Anionic Surfactants as Templates

Using a mixture of cetyltrimethylammonium bromide and carboxylate anionic surfactant (CnH2n+1COONa, n = 11, 13, 15, 17) as templates, siliceous MCM-48 is synthesized with low molar ratio (0.168:1) of mixed surfactants to silica and low concentration (5 wt %) of mixed surfactants.

Synthesis of MCM-41 with Different Pore Diameters without Addition of Auxiliary Organics

Swollen and highly ordered MCM-41 type materials with varied pores sizes, but with similar wall thicknesses, have been directly synthesized in the absence of auxilliary organics by controlling the preparation conditions. The most important parameter in the synthesis in order to control the pore opening is the cetyltrimethylammonium (CTMA+) concentration in the synthesis gel. Our results suggest that the mechanism of swelling is related with the replacement of some CTMA+ species by others cations in the interface formed between the liquid crystal and the silica surfaces. This approach could open new insights into the mechanism of formation of MCM-41 type materials as well as having in addition an important impact on the preparation of large mesoporous materials.

Synthesis of MCM-48 by a Phase Transformation Process

The ordered mesoporous silicate MCM-48 has been produced from MCM-41 by a phase transformation method, which involves heating the silicate samples while they are still incompletely polymerized. Ethanol, produced by hydrolysis of the silicate source TEOS, plays a crucial role in the transformation process. In this report, we examine samples produced using various combinations of stirring and heating times with XRD and 29Si MAS NMR and draw conclusions regarding the reasons for the transformation.

Synthesis and electron spin resonance studies of MCM-41 doped with copper pyridine complexes

Mesoporous MCM-41 materials have been synthesized and loaded with copper pyridine complexes by an ion-exchange procedure. Nitrogen adsorption and X-ray diffraction studies of the parent and loaded MCM-41 materials confirm the incorporation of the copper complexes into the mesopores of the MCM-41 structure. The incorporation status of the organometallic copper complexes is monitored by electron spin resonance and electron spin echo envelope modulation spectroscopy during the preparation procedure. Immobilized isolated copper pyridine complexes as well as agglomerates of complexes have been found in the ion-exchanged mesoporous material.

The Study of Ti-Mcm-41 by Transmission Electron Microscopy

Abstract In 1992, researchers at Mobil Research and Development created a new class of porous silicates, most notably MCM-41. This material features a hexagonal arrangement of pores and surface areas in excess of 1000 m2 g-1. Typically, MCM-41 exhibits pore diameters around 2.5 nm and a d-spacing around 4.0 nm, but slight variations in the synthesis of MCM-41 can produce a range of pore sizes from 2 to 10 nm. Zeolites, in comparison, have pore openings smaller than 1.3 nm and surface areas of a few hundred square meters per gram. Recently, Aronson et al. have been studying the grafting of TiO2 to MCM-41. TiO2 is a versatile photocatalyst in many selective organic oxidations and other reactions, including the degradation of environmental toxins. by dispersing TiO2 on the internal surface of a mesoporous support one can increase the active surface area significantly and introduce some size-selectivity.