Mesoporous Aluminosilicate Molecular Sieves Research Articles

Ruthenium supported on silicate and aluminosilicate mesoporous materials applied to selective sugar hydrogenation: Xylose to xylitol

A series of ruthenium-based catalysts supported on a set of silicate and aluminosilicate mesoporous molecular sieves was synthesized and tested in xylose hydrogenation. The materials were characterized in terms of morphology, textural properties, acidity, as well as ruthenium loading, dispersion, and oxidation state. In general, the aluminosilicates-based catalysts displayed a higher activity compared to their respective silicate supports, which can be ascribed to a higher Ru content and dispersion, enhanced by a higher acidity. The most active synthesized catalyst (Ru/Al-MCM-4) displayed an improved performance compared to a commercial Ru/C catalyst due to a better xylitol selectivity. Two modelling approaches were implemented to describe the kinetic rate. The first model was based on the hypothesis that xylose molecules and hydrogen are adsorbed in different active sites on the catalyst surface, while the second model supposes the formation of an intermediate on the catalyst surface that reacts to form xylitol. Both models gave a very good description of the experimental data.

Hydrogenation of toluene over nickel nanoparticles supported on SBA-3 and AlSBA-3 materials

Pure siliceous and aluminosilicate mesoporous molecular sieves of SBA-3 type were used as supports for nickel catalysts obtained via wet impregnation (1 wt.%). Characterization of obtained materials was performed by means of X-ray diffraction (XRD), X-ray fluorescence (XRF), low-temperature nitrogen adsorption/desorption (BET), temperature-programmed desorption of ammonia (TPD-NH3), hydrogen chemisorption measurements and temperature-programmed reduction with hydrogen (TPR-H2). The effect of nickel precursor (nickel nitrate or nickel acetate) and chemical composition of support (SBA-3 and AlSBA-3) on catalytic activity of prepared materials in toluene hydrogenation was studied. It was found that the catalysts obtained using nickel nitrate showed better preserved mesoporous structure with higher dispersion of Ni particles than catalysts obtained from nickel acetate. The use of AlSBA-3 as a support causes the formation of Ni particles with lower dispersion in comparison to the catalysts supported on SBA-3. The activity of nickel catalysts supported on the AlSBA-3 (especially the catalyst obtained using nickel nitrate) for toluene hydrogenation was higher than that of the catalyst supported on SBA-3 despite the lower Ni dispersion. The obtained results bring to conclusion that catalytic activity for toluene hydrogenation is significantly influenced by textural and chemical properties of the support.

Effect of nickel loading on hydrogen adsorption capacity of different mesoporous supports

Pure siliceous and aluminosilicate mesoporous molecular sieves of MCM-41 type have been used as support for nickel incorporation (2.5 wt%) by wet impregnation method. The hydrogen adsorption capacities at 77 K of these materials have been studied. Various techniques such as X-ray diffraction, N2 adsorption–desorption, X-ray photoelectron spectroscopy, Temperature-Programmed Reduction, UV–Vis diffuse reflectance spectroscopy and adsorption of pyridine coupled to infrared spectroscopy were employed to characterize the materials. In addition, Density Functional Theory calculations were used in order to interpret the results of hydrogen adsorption. The results obtained show that isolated metallic species are capable to promote hydrogen favorable sites. Isolated mononuclear Ni2+ species on the surface strengthen the interaction with the H2, enhancing the hydrogen adsorption capacity.

Selective synthesis of octahydroacridines and diannelated pyridines over zinc-containing mesoporous aluminosilicate molecular sieve catalysts.

We demonstrate a very eco-friendly and single-step catalytic method for the highly selective synthesis of 1,2,3,4,5,6,7,8-octahydroacridine (OHA) by the vapour phase aminocyclization of cyclohexanone (Cy[double bond, length as m-dash]O) with a mixture of formaldehyde (HCHO) and ammonia (NH3) over mesoporous bimetallic ZnAlMCM-41 (ZnAl-41) molecular sieves as efficient catalysts, which were synthesised by a simple basic hydrothermal method. To find optimum parameters for the synthesis of OHA, different reaction parameters, such as temperature, time on stream (TOS), weight hourly space velocity (WHSV), and feed molar ratios of Cy[double bond, length as m-dash]O : HCHO : NH3, have been extensively studied. The used ZnAl-41 catalysts were treated by washing and calcination to recover the recyclable catalysts which were then reused in these reactions to study their catalytic abilities. To selectively synthesize a variety of pyridine compounds, the active mesoporous catalysts, namely, ZnAl-41(75) and recyclable ZnAl-41(75), with different reaction parameters, were extensively used in the vapour phase aminocyclization reaction with different aldehydes and cycloketones, and produced excellent product selectivities, e.g., 9-alkyl substituted octahydroacridines (9-ASOHAs) and diannelated pyridines (DAPs), with good ketone conversions. In this catalytic reaction, OHA, 9-ASOHAs and DAPs are the main products and are important as starting materials in the preparation of biologically active compounds, drugs, dyes and alkaloids. It is shown by our remarkable catalytic results that the ZnAl-41(75) catalyst, as an environmentally friendly heterogeneous catalyst, has outstanding catalytic activity in the production of OHA, 9-ASOHAs and DAPs by a single-step synthetic method.

The catalytic stability of some selected bifunctional nanoporous-based catalysts in the hydroisomerisation of n-C7 and the effect of post-synthesis modification techniques

In this work, some commercial and in-house nanoporous-based catalysts, such as USY, beta and mordenite zeolites, and mesoporous aluminosilicate molecular sieves such as MCM-48 and SBA-15, loaded with metals and acting as mono- and bimetallic bifunctional catalysts, were used for hydroisomerisation experiments in a fixed-bed reactor at pressures between 1 and 15 bar and at feed space time ranging from 2.57 to 10.26 h−1 (35.14–140.6 kg s mol−1) to hydroisomerise n-heptane over a temperature range of 210–270 °C. The effect of post-synthesis treatments of micro- and mesoporous catalysts was examined, regarding their activity, selectivity and stability, such as acid and steam dealumination techniques, acid leaching via a chelating agent, bimetal loading techniques, different platinum loading methods, and composite or hybrid catalyst generation. Results show that pore architecture is the most important factor affecting coke formation and deactivation in zeolite catalysts. It was found that those catalysts with high Si/Al ratios and those which had been acid-leached or steamed showed better activity, higher selectivity towards isomeric products and better time stability. Moreover, the balance between the number of metal sites and the number of acid sites played an important role in determining the activity, selectivity and stability of the bifunctional catalysts. Higher metal loading improves catalytic stability, due to a better balance and closeness of the catalytic functions. Moreover, the bimetallic catalyst improves the formation of smaller metal particles and better dispersion, which may affect selectivity and stability.

Synthesis and characterization of ordered mesoporous aluminosilicate molecular sieve from natural halloysite

Currently, opening up the possibility of low-cost mineral for preparing ordered mesoporous materials is of significant importance. In the present work, hexagonally ordered mesoporous aluminosilicate molecular sieve was hydrothermally synthesized from natural halloysite without addition of silica or aluminum reagents. The mesoporous structure of the synthesized materials was confirmed by small angle X-ray diffraction and nitrogen sorption analysis. Scanning electron microscope and transmission electron microscope observations indicated that highly ordered two-dimensional hexagonal mesoporous structure was obtained. Wide angle X-ray diffraction and Fourier transform infrared spectroscopy were also used to examine the variations of chemical structures. The surface area of the prepared material after being calcined at 550°C was 524.6m2/g and the pore volume was 0.87cm3/g. 27Al solid state magic angle spinning nuclear magnetic resonance spectrum showed that all of aluminum species were tetrahedrally coordinated into the framework of the mesoporous material. A possible mechanism for the formation of aluminosilicate molecular sieves from natural halloysite was also discussed accordingly.

One-pot synthesis of mesoporous aluminosilicate as a novel solid acid catalyst for the alkylation of toluene with benzyl alcohol

One-pot synthesis of mesoporous aluminosilicate molecular sieve (MASM) with the Si/Al molar ratio of 25 from aluminium isopropoxide, tetraethylorthosilicate, acetylacetone as a chelating agent and cetyltrimethylaluminium bromide by the sol–gel method is reported. The solid product was characterized with XRD, FT–IR and nitrogen adsorption-desorption techniques. MASM successfully catalyzed the alkylation of toluene with benzyl alcohol with 100% conversion and 92% selectivity toward the formation of p-methyldiphenylmethane during 1 h.

Catalytic pyrolysis of oak via pyroprobe and bench scale, packed bed pyrolysis reactors

The pyrolytic conversion of oak sawdust at 500°C in flowing He over eight proprietary catalysts is described and compared to the control bed material, quartz sand. The reactions were conducted and compared in two reactors, an analytical, μg-scale pyroprobe reactor and a bench, g-scale packed bed reactor. The catalysts examined were modified acid catalysts, dealuminated-zeolite Y, β-zeolite, a naturally occurring metal hydroxide containing mineral, mordenite, and a mesoporous aluminosilicate molecular sieve. The packed bed reactor allowed the collection of three bulk product fractions, char, liquid, and gas, all of which could not be obtained from the μg-scale pyroprobe reactions. The catalysts effect on the mass balance of the bulk fractions tended toward more chars and less liquid compared to the sand control. The catalysts’ effects on the liquid products obtained in both reactors shifted away from acetic acid, furfural and higher molecular weight phenolics obtained with sand to lower molecular weight aromatics. This halved the total acid number of the liquid fraction and raised the pH by up to 1.4 units. The modified catalysts’ effects on the gas products from both reactors did not follow a specific trend. Instead, specific catalysts were able to enrich specific gas species up to a factor of 15 while suppressing the formation of others compared to the sand control. Two catalysts, β-zeolite and a naturally occurring metal hydroxide containing mineral, were regenerated and recycled up to five times with no loss of activity.

Calcium-Incorporated Mesoporous Aluminosilicates: Synthesis, Characterization, and Applications to the Condensation of Long-Chain Fatty Acid with Long-Chain Amine and Alcohol

A comprehensive study on a series of highly stable calcium containing mesoporous aluminosilicate molecular sieves (CaAlMMSH) having different acidic properties has been made by varying the Si/Ca ratio in synthesis gels. The structural, physical, and porous properties of these microporous/mesoporous composite materials were characterized by X-ray diffraction, N2 adsorption/desorption isotherm measurements, solid-state 27Al and 29Si magic angle spinning NMR, and variable-temperature hyperpolarized 129Xe NMR, Fourier transform infrared (FTIR) and diffuse reflectance FTIR spectroscopies. As compared to the parent AlMMSH materials, the incorporation of excessive amount of calcium tends to result in an overall increase in acid amount while at the expense of strong acid sites. The CaAlMMSH materials were found to have superior catalytic activities than AlMMSH in the amidation of palmitic acid with N-hexadecylamine. However, no significant enhancement in catalytic activity for the esterification of palmitic acid ...

Synthesis and Characterization of Ordered Mesoporous Aluminosilicate Molecular Sieves with High Stability in High‐Temperature Steam

AbstractThe ordered mesoporous aluminosilicate molecular sieve (MASMS‐1) stable in the high‐temperature steam has been successfully synthesized from the assembly of diluted ZSM‐5‐type precursor with mesoporous MCM‐41. The material was characterized by XRD, N2 adsorption‐desorption, FE‐SEM, TEM, FT‐IR spectroscopy and 27Al MAS NMR techniques. This mesoporous material shows high stability in the high‐temperature steam [H2O (ψ=20%) in N2 at 800 °C for 4 h], which might be ascribed to the synergistic effect of both thick walls containing zeolite‐like five‐membered ring subunits and highly condensed surface silanol groups.

Improvement of hydrothermal stability of an ordered mesoporous molecular sieve via multistage recrystallization

A highly ordered mesoporous aluminosilicate molecular sieve, designated as MSAMS-4, has been synthesized via multistage recrystallization. Hydrothermal-stability tests revealed that MSAMS-4 has retained a well-ordered hexagonal-symmetry mesostructure both after treatment with 100 °C water for 120 h and after steaming at 800 °C for 6 h.Key words: aluminosilicates molecular sieves, mesoporous materials, multistage recrystallization, hydrothermal stability.

Vapor-phase alkylation of toluene by benzyl alcohol on H 3PO 4-modified MCM-41 mesoporous silicas

Several mesoporous aluminosilicate molecular sieves with the MCM-41 structure (SiO 2/Al 2O 3 = 20–200) have been synthesized using different aluminum sources and modifying several synthesis parameters during the preparation process, such as the temperature and the content of water and sulfuric acid in the gel mixture. All samples were characterized by element chemical analysis, X-ray diffraction, N 2 physisorption, thermal analyses, and electron microscopy. These Al-MCM-41 materials have BET surface areas up to 940 m 2 g −1. The catalytic properties of their H 3PO 4-treated derivatives for Friedel–Crafts alkylation of toluene with benzyl alcohol have been evaluated. Toluene benzylation preferentially gave p-benzyl-toluene. The conversion of toluene to monoalkylated products increased with increasing the H 3PO 4 content in the catalysts and reached a maximum value for a H 3PO 4 loading of 25%, a further increase in H 3PO 4 leading to a decrease in the activity for alkylation. The influence of H 3PO 4 loading and of the operating parameters on the performance of the catalysts was also investigated.

Synthesis and characterization of mesoporous aluminosilicate molecular sieve from K-feldspar

Mesoporous aluminosilicate molecular sieves have been synthesized using K-feldspar, a natural ore rich in silicon and aluminum sources, as starting material. In this method, the mixture of K-feldspar and K 2CO 3 with mass ratio of 2:3 was first calcined at 880 °C for 1.2 h. The calcined materials were then dissolved in water together with cetyltrimethylammonium bromide as structure-directing agent, resulting in mesoporous molecular sieves after heating the solution at 130 °C for 60 h. Scanning electron microscopy and transmission electron microscopy observations indicated that the resulting materials were spherical particles with size of about 100 nm. The mesoporous structure of the as-synthesized materials was confirmed by low angle X-ray diffraction and nitrogen sorption analysis. The BET surface area of the as-prepared material after calcined at 550 °C was 507 m 2 g −1 and the pore volume was 0.854 cm 3 g −1. 27Al MAS NMR analysis showed that nearly all of aluminium is incorporated into the framework of the mesoporous material with 4-coordinated state. The acidity of the product was analyzed by FTIR spectroscopy of pyridine-adsorbed product. The product was treated in water at 100 °C for 360 h, and its mesoporous structure was still intact, suggesting its high hydrothermal stability.

Selective formation 2,6-diisopropyl naphthalene over mesoporous Al-MCM-48 catalysts

The protonated cubic mesoporous aluminosilicate (Al-MCM-48) molecular sieves have been synthesized hydrothermally and characterized by powder X-ray diffraction (XRD), nitrogen adsorption studies, thermogravimetric analysis (TGA) and solid-state 29Si and 27Al MAS NMR spectroscopy. The XRD patterns and nitrogen adsorption results reveal the cubic structural order and the mesoporous nature of the catalysts. 27Al MAS NMR spectra demonstrate that most of the Al is incorporated in the framework in tetrahedral coordination. Acidity measurement by pyridine-adsorbed FT-IR spectroscopy reveals that the incorporation of Al in the framework imparts substantial Brönsted acidity, which increases with increase in metal content. Lewis acidity is probably generated by extra-framework Al species. Vapour phase isopropylation of naphthalene (NAP) with isopropyl alcohol (IPA) was carried out over H-form of Al-MCM-48 catalysts with different n Si/ n Al ratios. The feed molar ratio of 1:2:10 (NAP:IPA:CYH) and WHSV (5.36 h −1) were found to be the optimized conditions for good NAP conversion with selectivity of 2,6-diisopropylnaphthalene (2,6-DIPN). The effect of 2,6/2,7-DIPN ratio was also studied for catalysts with various n Si/ n Al ratios and at different temperatures. Among the catalysts used in the present study, AlMCM-48 (25) showed a high NAP conversion and selectivity to 2,6-DIPN under the optimized reaction conditions.

Synthesis and catalysis of nanometer-sized bimodal mesoporous aluminosilicate materials

Nanometer-sized (below 100°nm) bimodal mesoporous aluminosilicate molecular sieves (NBMAS) are obtained by using sol–gel method and cetyltrimethylammonium bromide (CTAB) as the structure-directing agent. Ordering-packed framework mesopore is created within the colloidal particles by the templating function of surfactant CTAB and disordered textual pore is formed by the aggregation of colloidal particles as an inter-particle pore. As a result of the special properties of the present material, the hydrothermal stability and catalytic life of the material is highly improved in the catalytic cracking reactions. ZSM-5, normal AlMCM-41 and amorphous alumina–silica with nanometer particle size were used in the catalytic cracking process for comparing purpose.

Replication of Mesoporous Aluminosilicate Molecular Sieves (RMMs) with Zeolite Framework from Mesoporous Carbons (CMKs)

A novel class of mesoporous aluminosilicate molecular sieves has been prepared by replication from carbon mesoporous molecular sieves (CMKs) using zeolite precursors and characterized by a variety of analytical and spectroscopic techniques, such as XRD, N2 adsorption/desorption, SEM/TEM, IR, hyperpolarized (HP) 129Xe, and 31P MAS NMR. These replicated mesoporous materials (RMMs), namely RMM-1 and RMM-3 prepared from CMK-1 and CMK-3, were found to exhibit mesoporous structures respectively analogous to Al-MCM-48 and Al-SBA-15 but possess unique microporous characteristics due to the presence of zeolite secondary building units in the framework. Consequently, these RMMs are also found to have superior thermal, hydrothermal, and mechanical stabilities and with improved acidic properties compared to their respective parent counterparts. The RMM-3 so prepared represents the first synthesis of protonated aluminosilicate with an SBA-15 structure prepared by a nonacidic route.

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.

Preparation and characterization of aluminium – containing MCM-41

Mesoporous aluminosilicate molecular sieves with the MCM-41 structure (Si/Al=20) have been synthesized using tetraethoxysilane (TEOS) and sodium aluminate (NaAlO 2) as Si and Al sources and hexadecyltrimethylammonium bromide (HTMABr) and varying several parameters during the preparation process. All the samples were characterized by X-ray diffraction (XRD), Fourier transformed infrared (FT-IR) and solid state MAS NMR spectroscopy. A significant improvement in the structure by using a novel method for template removal has been evaluated.

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.

EPR studies of carbonaceous compounds deposited on Al-MCM-41

Electron paramagnetic resonance (EPR) spectroscopy was used to investigate carbonaceous compounds deposited on aluminosilicate mesoporous molecular sieves of the MCM-41 type during conversion of cyclohexene at various temperatures. The amount of the deposited coke grew with the increasing Al content of the catalysts and with the decreasing reaction temperature. The deposits caused a reduction in both the surface area and pore volume of the Al-MCM-41 materials. The measurements showed that the EPR lines were complex. The performed analysis revealed a hyperfine structure the envelope of which was of the Gaussian shape. It was found that the spin concentration increased and the peak-to-peak width (Δ B pp) decreased with the increasing reaction temperature.