Inside SBA-15 Research Articles

Synergistic Effect of Ethylene Glycol and Active Surface Group of SBA-15 under Ultrasound to Improve Catalytic Properties of Pd/SBA-15

Using ultrasonic methods in preparation of noble metal nanocatalysts is a hot spot in catalysis. In this paper, the synthesis of mesoporous material SBA-15 supported palladium catalyst Pd/SBA-15 was done by ultrasound assisted reduction and the synergistic effect between reductant and SBA-15 under ultrasound was discussed. The interaction of reductant ethylene glycol and active surface groups of SBA-15 under ultrasound led to the change in structure and surface properties of SBA-15, so that oxygen element in the structure of SBA-15 could chelate with palladium ions during impregnation, leading to the in-situ reduction of palladium nanoparticles(PdNPs) inside SBA-15. The obtained PdNPs in Pd/SBA-15 had a narrow size distribution and an average diameter of 2.98 nm. The yield of Suzuki coupling reaction between 4-bromotoluene and phenylboronic acid catalyzed by the prepared Pd/SBA-15 catalyst was 98.01%. And the results of recycle test proved the strong stability of Pd/SBA-15.

Hydrodeoxygenation of isoeugenol over Ni-SBA-15: Kinetics and modelling

Hydrodeoxygenation (HDO) of isoeugenol has been investigated over Ni-SBA-15 and Ni-SZ-SBA-15 containing sulfated ZrO2 with Si/Zr molar ratio of 8.4. The catalysts were prepared via incipient wetness method and characterized by N2 adsorption, AAS, TPR, X-ray diffraction (XRD), thermal gravimetric/differential thermal analyses (TG-DTA), organic elemental analysis, pyridine adsorption-desorption with Fourier-transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). The results revealed that 75% yield of propylcyclohexane was obtained over a non acidic Ni-SBA-15 in isoeugenol HDO at 300 °C under 3 MPa H2 using dodecane as a solvent. Ni-SZ-SBA-15 gave only very low HDO activity, which is explained by location of the acid sites both inside and outside SBA-15, whereas nickel particles were partially located inside the SBA-15 structure. On the other hand Ni particles in Ni-SBA-15 with the size of 20 nm were located outside SBA-15 promoting HDO. The kinetic model was developed for HDO of isoeugenol based on the proposed reaction network, which took into account formation of intermediate products as well as oligomers. The developed kinetic model was capable of describing well the experimental data with the degree of explanation equal to 91%. The activation energy for hydrogenation of propylcyclohexene and for demethoxylation of dihydroeugenol to 4-propylphenol are equal to 92 kJ/mol and 62 kJ/mol, respectively.

Effect of pore-directing agents and silanol groups in mesoporous silica nanoparticles as Nafion fillers on the performance of DMFCs

Pore-directing agents in SBA-15 and MSN mesopores could resist methanol crossover, while only P123 inside SBA-15 could assist proton transferring. But, highest proton conductivity was obtained on membranes with extracted MSN of high silanol contents.

New phase behavior of n-undecane–tridecane mixtures confined in porous materials with pore sizes in a wide mesoscopic range

Solid–liquid phase behaviors of normal alkane mixtures, undecane–tridecane (n-C11H24–C13H28, C11–C13), in bulk and adsorbed in SBA-15 and controlled porous glass (CPG) are investigated using differential scanning calorimetry (DSC) and temperature-dependent X-ray diffraction (XRD). The bulk C11–C13 mixtures display multiple phases due to the special rotator phase RI. In very small pores of SBA-15 (pore diameter d, 3.8 nm), the mixtures exhibit a curved melting boundary on heating. Inside SBA-15 (8.9 nm), the solid mixtures can form two-phase regions of mixed orthorhombic crystals with C11 and C13 packings (O11 + O13), and (RI + O13), which might include a possible RI phase in a narrow temperature range before melting. The solid mixtures confined in CPG (8.1 nm) also display two-phase regions (O11 + O13) and (RI + O13) and a possible RI phase in a small gap. The phase diagrams of the mixtures confined in SBA-15 (17.2 nm), CPG (46.4, and 300 nm) resemble to some extent that of the bulk system and appear in the close temperature range as well. The pore size exerts significant influence on the phase behavior of the C11–C13 mixtures under confinement. From the XRD analysis, the pore solid alkane molecules show effectively 2D arrangements confined in pores of diameter less than 20 nm while the lamellar ordering recovers in large pores of CPG (46.4, and 300 nm). The pore geometries of SBA-15 and CPG, the quasi one-dimensional vs. 3D connected network, also impact greatly on the phase behavior of the pore C11–C13 mixtures. Depression of the melting points and solid–solid transition temperatures of the pure C11 and C13 follows the Gibbs–Thomson equation confined in SBA-15, while it needs an extra term of d−2 in addition to the equation under confinement of CPG.

Effect of SBA-15 microporosity on the inserted TiO 2 crystal size determined by Raman spectroscopy

The effect of SBA-15 microporosity on the crystal size of TiO 2 was investigated employing SBA-15 materials with high (SBA-15-HM) and low (SBA-15-LM) microporosities (14.2% and 4.7% of microporous volume, respectively). TiO 2 phase was incorporated inside SBA-15 using internal hydrolysis method over a wide range of loadings (7–63 wt%). At all loadings, TiO 2 inside SBA-15 pores was in the form of anatase nanocrystals as found in characteristic Raman spectra. The crystal size of TiO 2 anatase phase was determined by Raman spectroscopy using a correlation between Raman peak position and peak width and TiO 2 crystal size. The correlation was established based on the set of unsupported TiO 2 samples with the crystals size in the range 5–120 nm (BET and XRD). Using this correlation, it was found that the crystal size of TiO 2 inside SBA-15 with high microporosity was lower than inside SBA-15 with low microporosity. This is a direct proof of the effect of wall microporosity on the dispersion of TiO 2 inside SBA-15. Due to the higher TiO 2 dispersion, TiO 2/SBA-15-HM adsorbed more vanadia than TiO 2/SBA-15-LM at the same TiO 2 loadings. As a result, V 2O 5/TiO 2/SBA-15-HM displayed higher activity than V 2O 5/TiO 2/SBA-15-LM in NO SCR with ammonia.

Influences of synthesis conditions and mesoporous structures on the gold nanoparticles supported on mesoporous silica hosts

Loading gold on mesoporous materials via different methods has been actively attempted in the literature, but the knowledge about the influences of synthesis details and different mesoporous structures on the size and thermal stability of gold nanoparticles supported on mesoporous hosts is still limited. In this study, Au/HMS, Au/MCM-41, Au/MCM-48, Au/SBA-15, and Au/SBA-16 samples were prepared by modifying a variety of mesoporous silicas by amine ligands followed by loading HAuCl 4 and calcination. The influences of different amine ligands ((3-aminopropyl)triethoxysilane versus N-[3-(trimethoxysilyl)propyl]ethylenediamine), solvents (water versus ethanol), calcination temperatures (200 or 550 °C), and mesoporous structures on the size of supported gold nanoparticles were systematically investigated employing nitrogen adsorption–desorption measurement, X-ray diffraction (XRD), diffuse reflectance UV–vis spectroscopy, and transmission electron microscopy (TEM). Interestingly, while big and irregular gold particles situate on MCM-48 with bicontinuous three-dimensional pore structure and relatively small pore size (2.4 nm) upon calcination at 550 °C, homogeneous and small gold nanoparticles maintain inside SBA-15 with one-dimensional pore structure and relatively big pore size (6.8 nm). Apparently, the pore structure and pore size of mesoporous silica hosts play a key role in determining the size and thermal stability of the supported gold nanoparticles. Our results may provide some useful clues for the rational design of supported metal catalysts by choosing suitable mesoporous hosts.

SBA-15-based polyamidoamine dendrimer tethered Wilkinson's rhodium complex for hydroformylation of styrene

Dendritic SBA-15 supported HRh(CO)(PPh 3) 3 catalysts were designed for liquid-phase hydroformylation of styrene. The silanols outside SBA-15 channels were passivated so that HRh(CO)(PPh 3) 3 complexes could be anchored mostly inside the SBA-15 channels. After passivation, PAMAM (polyamidoamine) dendrimers up to second generation were then grown inside the SBA-15 channels. Both pore size and dendrimer generation were found to influence the performance of catalysts for styrene hydroformylation, and the second-generation PAMAM was found to be optimal for these passivated dendritic SBA-15-supported rhodium catalysts. To study the effect of tethering HRh(CO)(PPh 3) 3 inside and outside SBA-15 mesopore channels, we also studied SBA-15-supported catalyst analogs with no passivation of external silanols. The passivated SBA-15 supported rhodium catalysts demonstrated an increase in catalytic activity and stability when the generation of supported dendrimer was increased from zeroth to second generation.

Direct Synthesis and Structural Characteristics of Ordered SBA-15 Mesoporous Silica Containing Tungsten Oxides and Tungsten Carbides

A series Of WO3-SBA-15 materials with different Si/W ratios have been hydrothermally synthesized using tetraethyl orthosilicate (TEOS) as silica precursor, ammonium paratungstate as tungsten precursor, and EO20PO70EO20 (P] 23) as structure-directing reagent. After temperature-programmed carburization (TPC) in flowing CH4/H-2 (20/80 v/v mixture), the materials were converted to the corresponding WxC-SBA- 15 materials. The structure of the oxide and carbide materials has been characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), nitrogen adsorption -desorption measurements, Si-29 magic-angle spinning (MAS) NMR spectroscopy, Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), and thermogravimetric and differential scanning calorimetric analysis (TG-DSC) measurements. The results show that after hydrothermal synthesis using different amounts of tungsten and subsequent carburization, the materials retain the mesopore structure of SBA- 15. When Si/W = 30-15, the majority of the tungsten is dispersed in the channels of SBA-15 with the remainder being incorporated into the framework of SBA-15 with the formation of Si-O-W bonds. The tungsten carbide exists as a single W2C phase after carburization. At higher tungsten content (Si/W = 7.5), the amount of tungsten in the framework of SBA-15 increases with the formation of both Si-O-W bonds and W-O-W bonds. The tungsten carbide formed after carburization exists as a mixture Of W2C and WC phases. A model for the distribution of tungsten in SBA-15 is proposed involving three different tungsten species: alpha-W inside SBA-15 channels, beta-W embedded in the internal surfaces of the SBA- 15 channels, and gamma-W inside the framework of SBA- 15. After temperature-programmed carburization, alpha-W sites are transformed into W2C, whereas beta-W sites afford WC; in contrast, gamma-W sites show little change after carburization.

Catalytic Aerobic Oxidation of Acetaldehyde over Keggin-type Molybdovanadophosphoric Acid/SBA-15 under Ambient Condition

Keggin-type molybdovanadophosphoric acids (HPA), H4PMo11VO40 (1), H5PMo10V2O40 (2) and H6PMo9V3O40 (3) were anchored onto γ-aminopropyltriethoxysilane (APTS) aminosilylated silica mesoporous SBA-15 through acid-base neutralization and the resulting HPA/APTS/SBA-15 were characterized by BET, TEM, XRD, ICP, FTIR and 31P MAS NMR. The characterization results indicate that the Keggin-structure of these HPAs is preserved within the mesoporous silica host. The samples were tested for catalytic aerobic oxidation of acetaldehyde heterogeneously in liquid phase under ambient condition. The electrostatic force between heteropoly acid and amino groups grafted on the silica channel surface leads to strong immobilization of HPA inside SBA-15 which is against the leaching during the reaction. The good catalytic performance and easy recycle of these catalysts make them as potential environmental friendly catalysts for elimination of indoor air pollutants.

High loading TiO 2 and ZrO 2 nanocrystals ensembles inside the mesopores of SBA-15: preparation, texture and stability

TiO 2 (30–80 wt.%) and ZrO 2 (48–75 wt.%) were inserted inside the pores of SBA-15 mesostructured silica host by chemical solution decomposition (CSD) or internal hydrolysis (IH) of the corresponding alkoxides. Both methods yielded composites with 85–94% TiO 2 crystallinity (anatase). In case of ZrO 2, CSD yielded >95% crystallinity (tetragonal phase), while IH gave an amorphous ZrO x -phase that does not crystallize up to 1073 K. The guest Ti(Zr)-oxide phases did not block the SBA-15 pores, and their surface was fully accessible for nitrogen adsorption. Calcination in air of TiO 2/SBA-15 and ZrO 2/SBA-15 (CSD) composites up to 1073 K did not change the nanocrystals structure and slightly increased the domain size derived from XRD data from 5.0–8.5 to 6–10 nm for TiO 2 (IH and CSD) and from 4.5 to 6.5 nm for ZrO 2 (CSD). After the same treatment the crystals domain size of bulk reference TiO 2 increased to >100 nm with full conversion to rutile polymorph and of reference bulk ZrO 2––to 20–25 nm with partial conversion to monoclinic modification. Thorough characterization of the texture, structure, location and dispersion by HRTEM, SAXS, EDS, SEM, XRD, N 2-adsorption methods allowed evaluation of the assembling mode of TiO 2 and ZrO 2 inside SBA-15 nanotubes: amorphous layer, ensemble of small 4–5 nm crystals (TiO 2-IH and ZrO 2-CSD) or single large 8.5 nm crystals (TiO 2-CSD).