Mesoporous SBA-15 Catalysts Research Articles

Highly Dispersed and Active Iron Oxide Nanoparticles in SBA-15 with Different Pore Sizes for the Synthesis of Diphenylmethane

Highly ordered mesoporous SBA-15 catalysts with different pore diameters decorated with various amounts of highly dispersed iron oxide nanoparticles were prepared by using a simple wet-impregnation technique. The structural order of the samples before and after the encapsulation of iron oxide nanoparticles were analysed by X-ray diffraction (XRD), BET nitrogen adsorption, high resolution scanning electron microscopy (HRSEM) and high resolution transmission electron microscope (HRTEM) whereas the nature and coordination of the iron oxide nanoparticles were obtained by ultraviolet-visible diffused reflection spectroscopy (UV-Vis DRS). Characterization results revealed that the iron oxide functionalized samples possess a well-ordered structure and excellent textural properties and the nanoparticles are highly dispersed inside the mesochannels of the SBA-15 supports. The size of the nanoparticles inside the mesochannels was also controlled by tuning the pore diameter of the supports whereas the amount of the nanoparticles was tuned by adjusting the amount of iron source in the synthesis mixture. Finally, these catalysts were tested for Friedel-Crafts benzylation of benzene and other aromatics with benzyl chloride (BC) as alkylating agent under liquid phase condition. All the samples exhibited excellent catalytic performance with a clean BC conversion and the selectivity to diphenylmethane (DPM). The influence of various reaction parameters such as substrate mole ratio, reaction time, reaction temperature and electron donating substituent moieties on the catalytic performance of iron oxide nanoparticles functionalized SBA-15 samples was also investigated. The catalysts showed 100% conversion of BC even at the reaction temperature as low as 50 °C which confirms a higher activity of these catalysts than that of other metal substituted mesoporous catalysts for the benzylation of benzene.

Sulfonic acid functionalized mesoporous SBA-15 catalysts for biodiesel production

Sulfonic acid functionalized mesoporous SBA-15 catalysts have been studied in the microwave-assisted transesterification of soybean oil with 1-butanol in order to produce low freezing point biodiesel. Small-angle powder XRD and nitrogen adsorption analysis revealed the formation of mesoporous materials with high surface area and uniform porosity. Catalytic activity was found to be largely dependent on the acid strength rather than the number of acid sites. Propyl-SO3H and arene-SO3H functionalized SBA-15 catalysts showed high activity and stability in transesterification reactions whereas perfluoro-SO3H functionalized SBA-15 catalyst exhibited a complete loss of activity after recycling due to complete leaching of perfluoro-SO3H groups in the reaction medium. The results over arene-SO3H functionalized catalysts showed that the optimal loading of arene-SO3H groups is approximately 15% (molar percent of functional group to total silicon) and the optimal oil to alcohol molar ratio is 1:6. Increases in catalyst to oil weight ratio and reaction temperature significantly enhance the reaction rates. Simultaneous transesterification and esterification of soybean oil with up to 20 wt% oleic acid over arene-SO3H functionalized catalyst indicated that this catalyst could be a promising candidate for processing low quality feedstocks containing high fraction of free fatty acids. Further modification of Ar-SO3H SBA-15 catalyst with hydrophobic groups did not significantly improve its catalytic performance.

Low temperature steam reforming of ethanol for carbon monoxide-free hydrogen production over mesoporous Sn-incorporated SBA-15 catalysts

This study investigated the application of a new metal catalytic species, Sn ion, rather than conventional Ni-based catalyst, to hydrogen production from ESR (ethanol steam reforming). Mesoporous SBA-15 catalysts with various contents of incorporated Sn (Sn-SBA-15) exhibited significantly higher ESR reactivity and the highest reactivity was achieved with 20 mol% Sn-SBA-15 catalysts: the H2 production and ethanol conversion were maximized at 75% and 92%, respectively, at a mild temperature of 500 °C for 1 h at a CH3CH2OH:H2O ratio of 1:1 and a GHSV (gas hourly space velocity) of 6600 h−1. The XRD (X-ray diffraction) and XPS (X-ray photoelectron spectroscopy) results indicated that the incorporated Sn species, SnO2/Sn, was simultaneously transferred to Sn/SnO2 by alternating their redox reactions and that the reactivity of the Sn-based activity could be long-lasting.

Polymerization of ethylene with (nBuCp)2ZrCl2 supported over mesoporous SBA-15 functionalized with sulfonic acid groups

The polymerization of ethylene in n-heptane with (nBuCp)2ZrCl2 supported over mesoporous SBA-15 catalysts functionalized with propyl or aryl sulfonic acid groups and impregnated with either MAO or TMA was investigated and compared with reference samples. All the supports showed mesoscopic ordering with pore sizes of 7.8–6.6nm, BET surface areas around 700m2g−1, sulfonic acid loadings between 10 and 20 wt% and an acidity of roughly 1–1.7mmol H+g−1. None of the catalysts were capable of polymerizing ethylene in the absence of MAO in spite of using TMA or TIBA as scavengers. The addition of MAO (Al/Zr=800 or 5000) led towards ethylene polymerization, being the activity dependent on Al/Zr molar ratio (higher for Al/Zr=5000). The catalysts treated with TMA during the impregnation exhibited considerable leaching, unlike those treated with MAO wherein the leaching was low (<9 wt%). The presence of the sulfonic acid moiety enhanced the activity of the catalysts. In addition, the activity was also augmented with the increase of the sulfonic acid content from 10 to 20 wt%. Interestingly, the molecular weight of the polyethylene synthesized with the SBA-15 functionalized with sulfonic acid groups were 1.5–2.5 times higher, especially with the propyl moiety which leads towards Mw∼350,000gmol−1 at 1.2barg. The results were explained through an interaction between the sulfonic acid moiety and the chlorinated MAO species, which activates the metallocene.

Highly efficient and clean synthesis of verbenone over well ordered two-dimensional mesoporous chromium silicate catalysts

Two-dimensional mesoporous SBA-15 catalysts synthesized by different hydrothermal methods have been used, for the first time, in the liquid-phase oxidation of α-pinene with t-butyl hydrogen peroxide (TBHP) for the synthesis of verbenone (V O). The recyclable CrSBA-15 catalysts have also been reused in this reaction to find their catalytic activities. To investigate the leaching of chromium species on the silica surface, CrSBA-15(8) has been treated with ammonium acetate solution, and it has been also treated with boiling water for the investigation of hydrothermal stability. The treated CrSBA-15(8) catalyst has been used in the catalytic reaction for finding the effects of catalytic stability. The influences of various reaction parameters such as temperature, time, ratios of reactant (α-pinene-to-TBHP) have been extensively investigated for the synthesis of V O. In addition, the liquid-phase oxidation of α-pinene has been conducted with different solvents to find the best solvent with a good catalytic activity. On the basis of all investigations with a hypothetical reaction pathway of α-pinene oxidation, the CrSBA-15(8) catalyst is found to be a highly active, recyclable and promising heterogeneous catalyst in the liquid-phase oxidation of α-pinene for highly selective synthesis of V O. Furthermore, CrSBA-15(8) catalyst has higher selectivity of V O (88.2%) than other CrSBA-15 and CrMCM-41.

Analytical pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS) of sawdust with Al/SBA-15 catalysts

Pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS) was employed to achieve fast pyrolysis of sawdust and on-line analysis of the pyrolysis vapors. A mesoporous SBA-15 catalyst and four Al/SBA-15 catalysts with different Si/Al ratios were prepared, and tests were performed to determine their effects on cracking the pyrolysis vapors. After catalysis, levoglucosan was significantly reduced or even completely eliminated. The yields of heavy furans and heavy phenols decreased significantly, while light furans and light phenols increased. Moreover, the catalytic cracking reduced the yields of light aldehydes and ketones, while increased the formation of acetic acid. Catalytic cracking also resulted in the formation of hydrocarbons, but their yields were not high. In regard to the four Al/SBA-15 catalysts, their effects on cracking the pyrolysis vapors were enhanced with the reducing of Si/Al ratios.

Zinc Carboxylate Functionalized Mesoporous SBA-15 Catalyst for Selective Synthesis of Methyl-4,4′-di(phenylcarbamate)

Mesoporous SBA-15 functionalized with zinc carboxylate (ZC/SBA-15) was used as a heterogeneous catalyst for the selective synthesis of methyl-4,4′-di(phenylcarbamate) (MDC) from dimethyl carbonate (DMC) and 4,4′-methylenedianiline (MDA). ZC/SBA-15 was prepared in three steps: first, SBA-15 grafted with –CN group was synthesized via the conventional one-pot route; then the –CN group was converted into –COOH group in H2SO4 solution; lastly, Zn2+ ions were introduced into the material by a facile ion-exchange process. The catalyst ZC/SBA-15 exhibits high MDA conversion (near 100%) and MDC selectivity (about 86.5%) with good recyclability in the MDC synthesis; this may provide a new approach for the non-phosgene synthesis of isocyanates.

DRIFTS Study on the Decomposition Mechanism of Mn Acetylacetonates Supported on SBA-15

Manganese oxides supported on mesoporous SBA-15 catalysts have been prepared by molecularly designed dispersion method, using Mn(II) and Mn(III) acetylacetonate organic precursors. XRD and in situ Raman studies demonstrate the formation of highly dispersed Mn2O3 and Mn3O4 nanoparticles on SBA-15 for the calcined samples. The detailed decomposition mechanism was studied by using in situ DRIFTS. Acetylacetonate ligands are stable up to 573 K and can only be completely removed by oxygen treatment.

Microwave assisted selective oxidation of lignin model phenolic monomer over SBA-15

Microwave assisted oxidation of the lignin model monomer apocynol, 1-(4-hydroxy-3-methoxyphenoxy)-ethanol was carried out over mesoporous SBA-15 catalyst using H2O2 as oxidant to produce acetovanillone, vanillin and 2-methoxybenzoquinone. Reaction conditions were optimised in order to obtain acetovanillone selectively, which serves as a raw material for 3,4-dimethoxybenzoic acid, a building block for synthesis of the smooth muscle relaxant mebeverin. Under conventional heating reactions were sluggish and gave poor yields of a mixture of products. The use of increased amount of catalyst resulted in lowering of acetovanillone selectivity. The possibility of recycling the catalyst was also studied.

Catalytic property of Pt/AlSBA-15 in selective catalytic reduction of NO

Pt-supported on mesoporous SBA-15 catalysts (Pt/SBA-15) have been investigated for selective catalytic reduction of NO by propene in excess oxygen. Catalytic activity of Pt/SBA-15 can be improved by the post-synthesis modification of A1 into SBA-15. The resulting material (A1SBA-15) retains a hexagonal order and physical properties of the parent SBA-15 and shows new acid sites. Increased acid sites are confirmed by NH 3 -TPD. Medium acid site appeared at 200 °C and broad strong acid site appeared above 250 °C. A certain degree of support acidity of Pt/A1SBA-15 increased the NO conversion, but when there are too many acid sites, carbon deposition becomes extensive and lead to decrease the NO conversion. The influence of different Pt loadings on the catalytic properties was also investigated.

Study of the benzylation of benzene and other aromatics by benzyl chloride over transition metal chloride supported mesoporous SBA-15 catalysts

The benzylation of benzene by benzyl chloride to diphenylmethane over FeCl 3, InCl 3, GaCl 3, ZnCl 2, CuCl 2 and NiCl 2 supported on mesoporous SBA-15 at 353 K has been investigated. The redox property due to the impregnation of the SBA-15 by transition metal chloride seems to play a very important role in the benzene benzylation process. Among the catalysts, the FeCl 3/SBA-15 showed both high conversation and high selectivity for the benzylation of benzene. The activity of these catalysts for the benzylation of different aromatic compounds is in the following order: benzene > toluene > p-xylene > anisole. More interesting is the observation that this catalyst is always active and selective for large molecules like naphthenic compounds such as methoxynaphthalene and he can also be reused in the benzylation of benzene for several times. Kinetics of the benzene benzylation over these catalysts have also been investigated.

Synthesis and characterization of tungsten-substituted SBA-15: An enhanced catalyst for 1-butene metathesis

Tungsten-substituted mesoporous SBA-15 materials have been successfully synthesized in a one-step co-condensation sol–gel method. The resultant materials have been characterized by X-ray diffraction (XRD), nitrogen adsorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), 29Si MAS NMR, UV–Visible spectroscopy and Raman spectroscopy. Results of these analyses indicate that the tungsten oxide species are highly dispersed in the silica-based framework structure. The tungsten-substituted mesoporous SBA-15 catalysts show excellent catalytic performance in the metathesis of 1-butene to high value olefins. The conversion of 1-butene is as high as 92.6% with metathesis selectivity reaching 68.3% which is more than double that of amorphous silica supported tungsten oxide catalyst (25.4%) prepared by the conventional impregnation method. The high dispersibility of tungsten oxide species, strong interaction between tungsten oxide species and silica as well as the pore structure of the tungsten-substituted mesoporous SBA-15 are critical factors leading to the excellent catalytic behavior.

Highly efficient tungsten-substituted mesoporous SBA-15 catalysts for 1-butene metathesis

Tungsten-substituted mesoporous SBA-15 materials have been synthesized by using a direct co-condensation sol–gel method. These resultant materials have been characterized by X-ray diffraction (XRD), nitrogen adsorption, transmission electron microscopy (TEM), 29Si MAS NMR and UV–Visible spectroscopy. Results of these analysis indicated that these materials had high surface area, uniform hexagonal channels and thick framework walls which were similar to that of SBA-15 and the tungsten species were highly dispersed in the silica-based framework structure. The tungsten-substituted mesoporous SBA-15 materials were used as catalysts for 1-butene metathesis for the first time, and they showed excellent catalytic performance. Such outstanding catalytic performance should be attributed to the proper content of tungsten species and its high dispersion.

Chromium Supported on Mesocellular Silica Foam (MCF) for Oxidative Dehydrogenation of Propane

A series of chromium-containing mesocellular silica foam (MCF) catalysts have been prepared and characterized in the oxidative dehydrogenation (ODH) of propane between 350 and 600 °C. It is demonstrated that the chromium catalysts supported on MCF exhibit much higher catalytic activity in terms of propane conversion and propylene yield than literature results obtained over chromium-supported mesoporous SBA-15 or MCM-41 catalysts during the ODH of propane. Enhanced catalytic performance of the chromium-containing mesoporous MCF catalysts has been attributed to the unique three-dimensional (3D), continuous, ultralarge mesopore structure of the MCF materials, which allow a much faster internal molecular transport during the ODH of propane.

Dehydrocondensation of alcohols to form ethers over mesoporous SBA-15 catalyst

A propylsulfonic acid-derivatized mesoporous SBA-15 catalyst was examined for activity and selectivity in the dehydrocondensation of methanol and isobutanol to form ethers, principally methyl isobutyl ether (MIBE) and dimethyl ether (DME), and dehydration of isobutanol to olefins, at elevated temperatures and pressures. It was shown that the catalyst maintained activity for > 1600 h , and the Brønsted acid sites corresponding to 1 meq/g of catalyst were stable under these reaction conditions until they were deliberately in situ poisoned by addition of pyridine. X-ray photoelectron spectroscopy (XPS) revealed that the pyridine was selectively and strongly adsorbed on the sulfonic acid groups. Kinetic studies demonstrated that MIBE and DME were formed by surface-catalyzed S N2 reactions that follow Langmuir–Hinshelwood kinetics involving competitive adsorption of the alcohols, while isobutene formation utilizes a vacant Brønsted acid site adjacent to the adsorbed isobutanol molecule. Isobutene formation rate exhibited a distinct maximum as a function of the alcohol pressure. This kinetic behavior is similar to that observed with Nafion-H and other catalysts. Because of the high apparent activation energy of isobutene synthesis compared with the much lower apparent activation energies of the ethers, lower reaction temperatures along with higher reactant pressures favor the formation of ethers over olefins. Theoretical modeling of the reaction pathway located stationary points including the transition states (TS) with barrier energies for all reactions involved, and showed that for ether synthesis one alcohol was adsorbed on a sulfonic acid site (I) via a donor H bond while the second alcohol was adsorbed on a proximal sulfonic acid site (II) via an acceptor H bond. In the intermediate, methyl transfer from the adsorbed methanol to the isobutanol oxygen occurs to form MIBE. At the same time, isobutanol donates its proton to a sulfonic acid group (II) whose oxygen acts as a base, and the methanol OH group accepts a proton from a sulfonic acid group (I) and is split off as water. To balance the surface charge, the original proton on sulfonic acid group (II) is transferred to sulfonic acid group (I), and MIBE is desorbed. The flexibility of the TS involving the concerted movement of all three protons is essential for the connectivity of the TS with the reactants and products and the umbrella inversion of the methyl group during its transfer. The theory has thus not only yielded a picture that is fully consistent with observed isotope flows, sp 3 carbon inversion, and temperature/pressure-dependent selectivity, but also revealed unprecedented detail of the concerted proton transfer and the role of acid–base interactions in this dual-site catalysis.

Vanadium oxide supported on mesoporous SBA-15 as highly selective catalysts in the oxidative dehydrogenation of propane

The combination of different techniques (DR UV–vis, 51V NMR, UV-Raman, FTIR, and H 2-TPR) in the characterization of vanadia supported on mesoporous SBA-15 catalysts shows that the dispersity and the nature of the vanadium species depend strongly on the V loading. In dehydrated catalysts with V contents lower than 2.8 wt%, vanadium is mainly in a tetrahedral environment. Higher V contents in the catalyst lead to the formation of polymeric V 2O 5-like species. Textural, SEM/TEM, and XRD results indicate that the ordered hexagonal mesoporous structure with large pore diameters of the support is retained upon the vanadium incorporation, and therefore high surface areas were obtained on the final catalysts. Vanadium species anchored to the surface show structural properties similar to those on mesoporous V-MCM and conventional VSiO 2 catalysts, but a higher surface concentration of isolated or low polymeric VO x species could be achieved on the V-SBA samples. The number and nature of the acid sites also change with the vanadium loading. The superior performance of the present mesoporous SBA-15 catalysts in the oxidative dehydrogenation of propane has been attributed to a higher dispersion of V species achieved on the SBA-15 support with large pore diameters as well as the low surface acidity of the catalyst.

Highly Effective Oxidative Dehydrogenation of Propane Over Vanadia Supported on Mesoporous SBA-15 Silica

Vanadia-containing mesoporous SBA-15 catalysts were prepared and characterized for the oxidative dehydrogenation (ODH) of propane. It is demonstrated that the vanadia-supported SBA-15 catalysts exhibit a much higher catalytic activity than those reported in the literature obtained over vanadium-supported mesoporous MCM-41 catalysts in the ODH of propane. The high catalytic performance of the mesoporous SBA-15 catalysts is attributed to the particularly large pore diameters and low surface acidity.

Sulfonic Acid-Functionalized Mesoporous Silica: Synthesis, Characterization, and Catalytic Reaction of Alcohol Coupling to Ethers

A propanesulfonic acid-derivatized mesoporous SBA-15 catalyst was synthesized, characterized in terms of surface properties, and shown to have high selectivities for alcohol coupling to form ethers, specifically from methanol and isobutanol coupling to form methyl isobutyl ether with no detectable formation of butenes at temperatures <400 K. Kinetic analysis was consistent with competitive adsorption of the two alcohols onto Bronsted acid sites, with isobutanol being more strongly adsorbed on the acid sites than the methanol.