Mesoporous Molecular Sieve MCM-41 Research Articles

The role of niobium in the gas- and liquid-phase oxidation on metallosilicate MCM-41-type materials

MCM-41 mesoporous molecular sieves containing Nb, V, and Mo separately and together have been synthesised and characterised by high-resolution transmission microscopy (HRTEM with EDX), N 2 adsorption isotherms, and X-ray diffraction (XRD), and tested in the oxidative dehydrogenation (ODH) of propane in the gas phase and in the liquid-phase oxidation of cyclohexene with hydrogen peroxide. For the first time, it has been documented that the incorporation of niobium during the synthesis of MCM-41 materials results in the formation of defects, the presence of which influences the selectivity in both reactions, ODH of propane to propene and epoxidation of cyclohexene. It is proposed that defect holes, generated by niobium, are convenient for access of reagents to the active species and for making the diffusion easier (particularly important in the liquid-phase reactions). NbO − species plays the role of an electronic promoter in multimetallosilicates NbV- and NbVMoMCM-41, where vanadium is an active species. In the absence of vanadium, niobium species are active in both oxidation processes. The role of acidity in the catalysts used for both oxidation processes is considered.

Comparison of Mesoporous Zn−Al−MCM-41 and Al−MCM-41 Molecular Sieves in the Production of p-Cymene by Isopropylation of Toluene

Mesoporous silica molecular sieves MCM-41 containing zinc and aluminum ions (Zn−Al−MCM-41) with Si/(Zn + Al) ratios equal to 75, 151, 228, 304, and 380 and only aluminum ions with Si/Al ratios equal to 21, 42, 62, 83, and 104 were synthesized under hydrothermal conditions using cetyltrimethylammonium (CTMA+) surfactants as templates 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 number of acid sites in Zn−Al−MCM-41 is higher than that in Al−MCM-41 due to the aluminum ion nonframework by the introduction of zinc ions. However, tetrahedral aluminum is replaced by zinc, producing two negative ions with a tetrahedral environment. The ions are associated with Bronsted acid sites, and the tetrahedral aluminum ions become octahedral aluminum ions and are associated with Lewis acid s...

Physico-chemical and catalytic properties of Ru–MCM-41 mesoporous molecular sieve catalyst: influence of Ru modification methods

The MCM-41 mesoporous molecular sieve was modified with Ru using in-situ synthesis, ion-exchange and impregnation catalyst preparation methods. The physico-chemical properties of the Ru–MCM-41 synthesized catalysts were studied using characterisation techniques such as X-ray powder diffraction, scanning electron microscopy, energy dispersive X-ray micro-analysis, X-ray fluorescence, XPS and nitrogen adsorption. The hydrogenation of cinnamaldehyde was used as a test reaction to evaluate the catalytic properties of the Ru–MCM-41 catalysts. The in-situ synthesis, ion-exchange and impregnation methods used for the introduction of Ru did not influence the parent structure and phase purity of the MCM-41 mesoporous molecular sieve under suitable designed synthesis conditions. At the same time the method of Ru introduction in MCM-41 was found to influence the physico-chemical and catalytic properties. The Ru–MCM-41 catalyst synthesized using in-situ synthesis resulted in the largest Ru crystallite size, which provided highest selectivity to the desired product cinnamyl alcohol and lowest conversion of cinnamaldehyde in the hydrogenation. The Ru–MCM-41 catalyst prepared by impregnation showed sintering of Ru particles, and lower selectivity to cinnamyl alcohol than the in-situ synthesized Ru–MCM-41 catalyst. The Ru–MCM-41 mesoporous molecular sieve catalyst prepared by ion-exchange showed the highest conversion of cinnamaldehyde, however formation of cinnamyl alcohol was not observed.

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

Pore-size control of mesoporous silica MCM-41 molecular sieve is described on the basis of the use of surfactant having different alkyl chain lengths and various organic auxiliary chemicals during the hydrothermal synthesis process. The BJH pore diameter of MCM-41 can be tuned from 1.6 to 4.2 nm using single or mixture of two surfactant(s) with alkyl chain lengths varied from C8 to C22. By the addition of different organic auxiliary chemicals: 1,3,5-trimethylbenzene, isopropylbenzene or tridecane into the synthesis medium, the BJH pore size of MCM-41 can be tailored up to 12.0 nm.

Dicyano-functionalized MCM-41 anchored-palladium complexes as recoverable catalysts for Heck reaction

Abstract Palladium(II,0) complexes were anchored on dicyano-functionalized MCM-41, producing new heterogeneous catalysts of the Heck reaction, which were synthesized via two-step surface modification of mesoporous molecular sieve MCM-41. The developed catalysts demonstrated easy separation after reaction, and reusability. BET, XRD, FT-IR, ICP-AES, H2 chemisorption as well as XPS techniques were employed to characterize the catalytic materials.

Ordered mesoporous MCM-41 silicon oxynitride solid base materials with high nitrogen content: synthesis, characterisation and catalytic evaluation

We present here the synthesis, physicochemical characterisation and catalytic evaluation of mesoporous silicon oxynitride materials. The solid base catalytic materials were prepared by subjecting pure silica MCM-41 mesoporous molecular sieves to nitridation, i.e., treatment with ammonia at high temperature. The mesoporous MCM-41 silicon oxynitride materials are well ordered and possess high surface area and pore volume. The nitrogen content was controlled within the range 8.6 to 25.1 wt% by simply changing the nitridation temperatures (between 850 and 1150 °C) or the time allowed for nitridation (from 20 to 80 hours). The nitrogen is incorporated onto the MCM-41 framework in the form of various NHx species, including terminal NH2 and bridging NH groups as well as adsorbed ammonium ions. The oxynitride materials were found to exhibit considerable catalytic activity for the Knoevenagel condensation reaction. The catalytic activity was correlated to the nitrogen content and was therefore highest for materials nitrided at high (1150 °C) temperature. In all cases, the nitrided materials were found to be generally stable with respect to storage and they suffered no significant structural degradation over a period of a few months. Oxynitride materials with the highest nitrogen content (i.e., those nitrided at temperatures ≥1050 °C) were found to be more susceptible to loss of surface area and pore volume after storage under ambient conditions for 6 months. The ease of preparation and control of the nitrogen content of mesoporous oxynitride materials and their stability makes them attractive as alternative solid base catalysts especially for large molecule transformations.

Adsorption separation of CO<SUB align=right>2 from simulated flue gas mixtures by novel CO<SUB align=right>2 "molecular basket" adsorbents

Adsorption separation of CO2 from simulated flue gas mixtures containing CO2, O2, and N2 by using a novel CO2 "molecular basket" adsorbent was investigated in a flow adsorption separation system. The novel CO2 "molecular basket" adsorbents were developed by synthesising mesoporous molecular sieve MCM-41 and modifying it with polyethylenimine (PEI). The influence of operation conditions, including feed flow rate, temperature, feed CO2 concentration, and sweep gas flow rate, on the CO2 adsorption/desorption separation performance and CO2 breakthrough were examined. The CO2 adsorption capacity was 91.0 ml (STP)/g-PEI, which was 27 times higher than that of the MCM-41 alone. Further, the adsorbent showed separation selectivity of greater than 1000 for CO2/N2 ratio and approximately 180 for CO2/O2, which are significantly higher than those of the MCM-41, zeolites, and activated carbons. Cyclic adsorption/desorption measurements showed that the CO2 "molecular basket" adsorbent was stable at 75°C. However, the CO2 "molecular basket" adsorbent was not stable when the operation temperature was higher than 100°C.

CuCl2Immobilized on Amino-Functionalized MCM-41 and MCM-48 as Efficient Heterogeneous Catalysts for Dimethyl Carbonate Synthesis by Vapor-Phase Oxidative Carbonylation of Methanol

Pure silica mesoporous molecular sieves MCM-41 and MCM-48 organofunctionalized with 3-aminopropyltrimethoxysilane and N-[(3-trimethoxysilyl)propyl]ethylene-diamine, respectively, were served as supports to immobilize CuCl2 with conventional impregnation method. The supported copper catalysts showed a considerable enhancement in the reaction rate in heterogeneous vapor-phase oxidative carbonylation of methanol to produce dimethyl carbonate in comparison with that obtained by CuCl2-supported nonfunctionalized mesoporous silicas under identical conditions. The electronic donation of the amino groups, the accessibility and dischargeability of reactants in the regular mesopores probably account for the good catalytic performance as evidenced by the characteristic studies with XRD, BET, FTIR, TG-DTA, and XPS.

Template synthesis and characterisation of MCM-41 mesoporous molecular sieves containing various transition metal elements—TME (Cu, Fe, Nb, V, Mo)

A series of metallosilicates (transition metal elements—TME) MCM-41 (TME=Fe, Cu, Nb, V, Mo) mesoporous molecular sieves with variable Si/TME ratios have been synthesized and characterised by low temperature N 2 adsorption/desorption, XRD, XPS, H 2-TPR, FTIR combined with NO+NO 2 adsorption, diffuse reflectance UV–Vis spectroscopy, and ESR study. All the materials exhibit hexagonal arrangement of uniform mesopores (with exception of CuMCM-41). Defect holes amid the nanochanels besides well-ordered mesopores characterise mainly Fe-containing materials, in which the highest TME loading was reached. Similar but smaller defects take place in NbMCM-41. The amount of TME included into MCM-41 structure under the preparation conditions used in this work changes in the order: Fe>Nb>Cu≫V≫Mo. This sequence is not related to the oxidation state of metals which was estimated in calcined materials as Fe 3+, Nb 5+, Cu 2+, V 5+, Mo 6+. It does not also correlate with cation sizes in a simple way. The possibility of forming tetrahedral coordination seems to limit the TME incorporation into the MCM-41 skeleton if free metal cations are used in the gel (Cu 2+, Fe 3+, Nb 5+). Al in the gel makes the isomorphously substitution of silicon by copper easier, but part of Cu occupies extra framework cationic positions in the final material.

Vapor-phase silylation of MCM-41 and Ti-MCM-41

MCM-41 mesoporous molecular sieves have been silylated with trimethylchlorosilane (TMCS) and trimethylethoxysilane (TMES) under anhydrous, vapor-phase reaction conditions. The silylation reactions were performed at 473 and 623 K following pre-treatment at either 523 or 973 K. At the pre-treatment temperature of 973 K, most hydrogen-bonded surface silanols in MCM-41 are dehydroxylated to form siloxane bridges. The reactivity of surface silanols and siloxane bridges with the silylation agents was monitored using in-situ infrared spectroscopy. More extensive silylation by TMCS and TMES is achieved at the higher reaction temperature. At 623 K, TMCS reacts with most lone and hydrogen-bonded silanols in non-dehydroxylated MCM-41 to yield a trimethylsilyl (TMS) surface coverage of approximately 1.2 TMS/nm 2. Silylation protocols incorporating the dehydroxylation pre-treatment step yield lower organic loadings, because the siloxane bridges do not completely react with the silylation agents or their co-products. Silylation of titanium-containing MCM-41 catalysts with TMCS enhances their hydrophobicity and improves their activity and selectivity for the epoxidation of cyclohexene with aqueous hydrogen peroxide.

Studies on the state of iron oxide nanoparticles in MCM-41 and MCM-48 silica materials

Phase transformations in and the reductive and catalytic properties of mesoporous MCM-41 and MCM-48 silica molecular sieves modified with iron oxide were studied by X-ray diffraction, nitrogen physisorption, Mössbauer spectroscopy, temperature-programmed reduction, and methanol decomposition as a catalytic test. Their behavior is compared to that of the related bulk materials. Various types of iron species with different properties were identified.

Preparation and characterization of novel CO 2 “molecular basket” adsorbents based on polymer-modified mesoporous molecular sieve MCM-41

Novel CO 2 “molecular basket” adsorbents were prepared by synthesizing and modifying the mesoporous molecular sieve of MCM-41 type with polyethylenimine (PEI). The MCM-41-PEI adsorbents were characterized by X-ray powder diffraction (XRD), N 2 adsorption/desorption, thermal gravimetric analysis (TGA) as well as the CO 2 adsorption/desorption performance. This paper reports on the effects of preparation conditions (PEI loadings, preparation methods, PEI loading procedures, types of solvents, solvent/MCM-41 ratios, addition of additive, and Si/Al ratios of MCM-41) on the CO 2 adsorption/desorption performance of MCM-41-PEI. With the increase in PEI loading, the surface area, pore size and pore volume of the PEI-loaded MCM-41 adsorbent decreased. When the PEI loading was higher than 30 wt.%, the mesoporous pores began to be filled with PEI and the mesoporous molecular sieve MCM-41 showed a synergetic effect on the adsorption of CO 2 by PEI. At PEI loading of 50 wt.% in MCM-41-PEI, the highest CO 2 adsorption capacity of 246 mg/g-PEI was obtained, which is 30 times higher than that of the MCM-41 and is about 2.3 times that of the pure PEI. Impregnation was found to be a better method for the preparation of MCM-41-PEI adsorbents than mechanical mixing method. The adsorbent prepared by a one-step impregnation method had a higher CO 2 adsorption capacity than that of prepared by a two-step impregnation method. The higher the Si/Al ratio of MCM-41 or the solvent/MCM-41 ratio, the higher the CO 2 adsorption capacity. Using polyethylene glycol as additive into the MCM-41-PEI adsorbent increased not only the CO 2 adsorption capacity, but also the rates of CO 2 adsorption/desorption. A simple model was proposed to account for the synergetic effect of MCM-41 on the adsorption of CO 2 by PEI.

Ruthenium-modified MCM-41 mesoporous molecular sieve and Y zeolite catalysts for selective hydrogenation of cinnamaldehyde

Ru-modified MCM-41 mesoporous molecular sieve and Y zeolite catalysts were synthesised and characterised using XRD, electrochemical voltammetry, ESCA (XPS), nitrogen adsorption and H 2-TPD. Selective liquid-phase hydrogenation of cinnamaldehyde to cinnamyl alcohol was investigated over these catalysts and compared to hydrogenation on a commercial Ru/C catalyst. The effect of support (MCM-41, Y and C), solvent (cyclohexane, hexane and 2-propanol) and catalyst pre-treatment (calcination) on the conversion of cinnamaldehyde and selectivity to cinnamyl alcohol was studied. The zeolite structure, pore size, acidity, catalyst pre-treatment as well as the solvent influenced the activity and selectivity. Non-calcined Ru/Y exhibited the highest selectivity to cinnamyl alcohol. The activity of Ru/Y was highest with 2-propanol as a solvent.

Rh(cod)Cl]2 complex immobilized on mesoporous molecular sieves MCM-41-a new hybrid catalyst for polymerization of phenylacetylene

Abstract A new hybrid catalyst affording polymerization of phenylacetylene (PhA) into high-molecular-weight (Mw = 180 000) high-cis-polyphenylacetylene (PPhA) was prepared via immobilization of [Rh(cod)Cl]2 (cod=η4-cycloocta-1,5-diene) on siliceous mesoporous molecular sieves MCM-41 modified by 3-aminopropyltrimethoxysilane. The polymerization was confirmed to proceed on anchored Rh-species and PPhA formed was continuously released into liquid phase, from which it was easily isolated. In comparison with related homogeneous catalysts, the hybrid catalyst provided comparable or even higher PPhA yields, considerably higher molecular weight of PPhA and reduced amounts of oligomeric by-products. The catalyst was found to be resistant to Rh leaching; however, chemical transformation of anchored Rh-species occurring during polymerization strongly reduced the possibility of catalyst re-using.

Active copper species in 1-butene skeletal isomerization: comparison between copper-modified MCM-41 and beta catalysts

The role of copper was studied in the skeletal isomerization of 1-butene over copper-modified mesoporous MCM-41 molecular sieve and Beta zeolite. The Cu–H-MCM-41 and Cu–H-Beta catalysts were synthesized in our laboratory and characterized by XRD, nitrogen adsorption, X-ray fluorescence, FTIR of adsorbed pyridine and direct current plasma atomic emission spectrometry. The oxidation state of copper after oxidation and reduction in Cu–H-MCM-41 was evaluated by FTIR with probe molecules. Copper ion-exchanged and the proton forms of MCM-41 and Beta catalysts were tested towards 1-butene skeletal isomerization by varying the weight hourly space velocity and temperature. Quantum chemical calculations at the B3LYP/6-31 + G ** level were performed in order to understand the role of copper at the molecular level. Copper in Cu–H-MCM-41 pretreated in synthetic air was mostly in the form of Cu 2+ but reduced during the catalytic experiment to the metallic form Cu 0 via Cu +. Even if the copper exchange decreased the amount of Brønsted acid sites, Cu–H-MCM-41 pretreated in synthetic air was more active than H-MCM-41 towards 1-butene skeletal isomerization. The enhanced catalytic activity is due to copper Cu +, which was formed during the reaction. Introduction of copper into H-Beta, however, did not have any effect at all on the performance of the catalyst. The probable reason for this is the high initial activity of copper-modified H-Beta causing a very fast reduction of copper to the inactive metallic form Cu 0.

Catalytic conversion of palm oil over mesoporous aluminosilicate MCM-41 for the production of liquid hydrocarbon fuels

The catalytic cracking of palm oil to liquid hydrocarbon fuels was studied in a fixed bed micro-reactor operated at atmospheric pressure, reaction temperature of 723 K and weight hourly space velocity (WHSV) of 2.5 h −1 over the synthesized mesoporous molecular sieve MCM-41 materials. Mesoporous aluminosilicate with Si/Al ratio of 50 was synthesized using the hydrothermal method. Different pore sizes were obtained by changing the type of template and organic directing agent (ODA) used. The synthesized materials were characterized using various analytical methods such as X-ray powder diffraction (XRD), BET surface area, inductive coupled plasma (ICP), MAS NMR, FTIR and temperature-programmed desorption (TPD). The materials exhibit a crystalline structure of MCM-41 mesoporous molecular sieves with surface area varyng from 550 to 1200 m 2/g and an average pore size (APS) ranging from 1.8 to 2.8 nm. The synthesized MCM-41 catalysts show high activity for palm oil cracking. The conversion of palm kernel oil, lower-molecular-weight oil, was higher as compared to higher-molecular-weight, palm olein oil. MCM-41 materials were selective for the formation of linear hydrocarbons, particularly, C 13 when palm kernel oil was used and C 17 when palm olein oil was fed. The yield of liquid product decreased with the increase of surface area of the catalyst. The gasoline selectivity increased whereas diesel selectivity decreased with the conversion of palm oil.

The effect of phosphate treatment on nickel dispersion on MCM-41 mesoporous material

The incorporation of nickel into mesoporous molecular sieves MCM-41 was carried out. Ni-PO/MCM41 and Ni-C1/MCM41 were prepared by using Ni(II) acetate solution adjusted to pH=2.5 with phosphoric acid and hydrochloric acid, respectively, by the incipient wetness method. Photoacoustic spectroscopy (PAS) was used to study the local environments of Ni(II) incorporated into mesopores. The PAS of as-prepared Ni/MCM41, Ni-Cl/MCM41, and Ni-PO/MCM41 with Ni(II) acetate solution exhibits two bands of λmax around 400 nm and 750 nm, which could be assigned to the3A2g→3Tlg(F) and the3A2g→3Tlg(P) transition of octahedral Ni(II) species. After calcination, Ni ion within Ni-PO/MCM41 dispersed atomically onto the surface of MCM-41 channel as an octahedral species without the transformation to nickel oxide phase, while Ni ion within Ni-Cl/MCM41 and Ni/MCM41 transformed to nickel oxide phase. It may be attributed to the fact that each Ni ion is separated by the phosphate grafted to surface silanol group. The effects of phosphoric acid on the dispersity of Ni ion within MCM-41 have been investigated using31P and29Si MAS NMR spectroscopy and X-ray photoelectron spectroscopy.

Allylic oxidation of cyclohexene over chromium containing mesoporous molecular sieves

Allylic oxidation of cyclohexene was carried out over mesoporous (Cr)MCM-41 and (Cr)MCM-48 molecular sieve catalysts. In both the cases, 2-cyclohexen-1-one was obtained as the major product with small amounts of cyclohexene oxide and 1,2-cyclohexandiol. (Cr)MCM-48 showed higher activity than (Cr)MCM-41 owing to the high chromium content in the former. The use of polar solvents such as acetonitrile and methanol decrease the 2-cyclohexen-1-one selectivity; however, such a procedure produces double bond oxidized product, viz. cyclohexene oxide. Furthermore, unlike many other chromium-based solid catalysts, the activity over recycled as well as washed (Cr)MCM-41 and (Cr)MCM-48 remains nearly the same, indicating that the mesoporous chromosilicate materials behave truly as heterogeneous catalysts. In other words, after the initial loss of non-framework chromium ions for the first time, no leaching was noticed for the chromium-based systems.

Mesoporous Al-containing MCM-41 molecular sieves: highly active catalysts for Diels–Alder reaction of cyclopentadiene with α,β-unsaturated aldehydes

We investigated the liquid phase Diels–Alder reaction of cyclopentadiene with α,β-unsaturated aldehydes (at 37 °C) over mesoporous Al-containing MCM-41 molecular sieves, with different Si/Al ratios, prepared by four different methods—sol–gel, hydrothermal, grafting and template cation exchange. The catalysts have been characterized for their phase purity, surface area, average pore size and acidity. The Al-containing MCM-41 catalysts prepared by different methods behaved differently in the acid-catalyzed Diels–Alder reaction. Among the different MCM-41 catalysts (having almost the same Si/Al ratio), Al:MCM-41, prepared by grafting method showed the highest activity in the Diels–Alder reaction of cyclopentadiene with crotonaldehyde, which may be due to its higher acidity. The introduction of Al into the framework of MCM-41 increased the acidity; however, the increase in the acidity up to an optimum level increased the activity. Al:MCM-41 catalyst is more catalytically active in the Diels–Alder reaction than the heterogeneous solid acids—mesoporous SBA-15, microporous H-ZSM-5 and HY zeolites, amorphous silica–alumina, amberlist 15, active alumina, silica gel and homogeneous acid catalysts— p-toluenesulfonic acid and AlCl 3.

Aluminum incorporation in mesoporous MCM-41 molecular sieves and their catalytic performance in acid-catalyzed reactions

Mesoporous aluminosilicate molecular sieves, Al-containing MCM-41, with different Si/Al ratios were synthesized by four different methods: sol–gel, hydrothermal, template cation exchange and grafting. The catalysts prepared by sol–gel, grafting and template cation exchange methods are effective for the incorporation of large amounts of aluminum into the framework of MCM-41. The catalytic activities of the resulting Al-containing MCM-41 samples were tested in the cracking of cumene and the dehydration of 2-propanol, as model acid-catalyzed reactions, and then compared with the results obtained from microporous H-ZSM-5 and HY zeolites. The Al-containing MCM-41 catalysts prepared by different methods behaved differently in acting as acidic catalysts; the catalyst (having almost same Si/Al ratio) prepared by sol–gel method showed higher cracking activity, whereas that prepared by template cation exchange method showed higher dehydration activity. Moreover, these Al-containing MCM-41 catalysts are more catalytically active than microporous HY zeolite for cumene cracking and 2-propanol dehydration reactions.