Sulfonic acid functionalized mesoporous SBA-15 for selective synthesis of 4-phenyl-1,3-dioxane

Mesoporous SBA-15 silica has been functionalized with propylsulfonic acid groups post-synthetically using 3-mercaptopropyltrimethoxysilane as sulfur source. The materials before and after functionalization have been characterized by BET surface area and pore size distribution by BJH method, powder X-ray diffraction and temperature programmed desorption (TPD) of NH₃. The resultant mesoporous material (solid acid catalyst) exhibited hexagonal mesoscopic ordering, which possess 1.3 meq H⁺ g⁻¹ SiO₂ exchange capacity, 96 Å mesopore size diameter, and 660 m² g⁻¹surface area. Sulfonic acid groups anchored to SBA-15 silica pore surfaces are thermally stable up to 653 K, hydrothermally robust in boiling water and resistant to leaching in organic and aqueous solvents under mild conditions. XRD results indicate that there is no change in the structure after anchoring SBA-15 with SO₃H group. SBA-15-SO₃H catalyst has been found to be highly active and selective for the Prins condensation of styrene with formaldehyde. Both the conversion of styrene and the selectivity to 4-phenyl-1,3-dioxane are nearly 100%. Presence of more number of acid sites in SBA-15-SO₃H catalyst helps in achieving high yields. Furthermore, the conversion and the selectivity to 4-phenyl-1,3-dioxane are found to be consistent in four repeated cycles.     

Arenesulfonic acid functionalized ordered mesoporous silica as solid acid catalyst for solvent free dehydration of sorbitol to isosorbide

Organosulfonic acid functionalized ordered mesoporous silicas with different moieties have been synthesized and used as solid acid catalysts for solvent free dehydration of sorbitol to isosorbide. In screening experiments with distinct solid acids, the arenesulfonic acid functionalized SBA-15 (Ar/SBA-15) showed higher catalyst performance as compared to propyl and fluorosulfonic acid sites. Under optimum reaction condition, Ar/SBA-15 afforded 100% sorbitol conversion with 71% isosorbide selectivity in 2 h at moderate temperature of 170 °C. The high activity of catalyst ascribed to its ordered mesoporous structure and ease to access Brönsted acid sites with high acid strength.     

Control of amine functionality distribution in polyvinylamine/SBA-15 hybrid catalysts for Knoevenagel condensation

Poly(N-vinylformamide) was deposited on the surface of highly ordered hexagonal mesoporous silica SBA-15 by in situ polymerization. Acid-catalyzed hydrolysis followed by neutralization with NaOH (pH = 7.0–10.0) allowed obtaining the poly(vinylamine)/SBA-15 hybrid materials with various distributions of N-containing species, which were determined by XPS and DRIFT spectroscopy. The changes in the form of deposited polymer as well as its interaction with the silica support were discussed. The poly(vinylamine)/SBA-15 materials were tested as catalysts of Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate, ethyl acetoacetate and diethyl malonate. It was found that the sample neutralized at pH = 9.0 showed the best catalytic performance, which was attributed to a high content of accessible NH₂ groups.     

SBA-15-supported ionic liquid compounds containing silver salts: Novel mesoporous π-complexing sorbents for separating polyunsaturated fatty acid methyl esters

Novel π-complexing sorbents were prepared by covalently immobilizing ionic liquids (ILs) onto mesoporous SBA-15 using a one-pot sol–gel process followed by coating these SBA-15-supported IL compounds with silver salts. The mesoporous π-complexing sorbents were characterized by small angle X-ray scattering (SAXS), FTIR, TEM, SEM, nitrogen adsorption desorption isotherm, NMR, and nitrogen elemental analysis. Two advantages were obtained using these novel mesoporous π-complexing sorbents versus the traditional π-complexing sorbents formed by directly anchoring silver salts onto silica gel. (1) Higher extraction capacities were found. The extraction capacity for the polyunsaturated fatty acid methyl ester (PUFAME), methyl all-cis-5,8,11,14,17-eicosapentaenoate (20:5 or EPA), was 195 mg/g sorbent using the mesoporous AgBF₄/SBA-15 · IL · PF₆ sorbent. The capacity decreased to 121 mg/g sorbent with microporous complexing sorbent AgBF₄/SiO₂ · IL · PF₆. (2) Better reusability was also achieved. The supported IL phase immobilized and retained silver salt on SBA-15 due to the interaction between the ionic liquid’s imidazolium cations and silver ions. Eight successive sorption runs with the AgBF₄/SBA-15 · IL · PF₆ sorbent showed a satisfactory reusability. The traditional π-complexing sorbent has a silver salt directly anchored on silica without the supported ionic liquid phase. Higher silver leaching into organic solution occurred from the AgBF₄/SBA-15 sorbent determined by ICP-AES. The combined percentage (wt%) of the omega-3 PUFAMEs: 20:5 and methyl all-cis-4,7,10,13,16,19-docosahexaenoate (22:6 or DHA) stripped from the AgBF₄/SBA-15 · IL · PF₆ by 1-hexene was significantly enriched from 18% in the original cod liver oil to 90.5%.     

New mesoporous carbon materials synthesized by a templating procedure

The new porous carbon materials were obtained by templating procedure using mesoporous silica (SBA-15) as template. The ordered mesoporous silica materials were synthesized by using Pluronic P123 (non-ionic triblock copolymer, EO₂₀PO₇₀O₂₀). SBA-15/cryogel carbon composites were obtained by sol–gel polycondenzation of resorcinol and formaldehyde in the presence of different amount of SBA-15. The polycondenzation was followed by freeze drying and subsequent pyrolysis. One set of SBA-15/sucrose carbon composites was prepared by using sucrose as carbon source. The silica template was eliminated by dissolving in hydrofluoric acid (HF) to recover the carbon material. The obtained carbon replicas were characterized by nitrogen adsorption–desorption measurements, X-ray diffraction and scanning electron microscopy (SEM). It was revealed that the samples have high specific surface (533–771 m² g^?1), developed meso- and micro-porosity and amorphous structure. Porous structure of carbon replicas was found to be a function of the carbon source, properties of SBA-15 and silica/carbon ratio. Room temperature adsorption of nitrogen and adsorption of phenol from aqueous solutions were investigated.     

Effects of Fe addition on the structure and catalytic performance of mesoporous Mn/Al–SBA-15 catalysts for the reduction of NO with ammonia

Mesoporous Al–SBA-15 has been synthesized by a hydrothermal method and used as a support for Mn/Al–SBA-15, Fe/Al–SBA-15, and Mn–Fe/Al–SBA-15 catalysts. XRD, N₂ sorption, XPS, H₂-TPR and activity tests have been used to assess the properties of catalysts. The Mn–Fe/Al–SBA-15 catalyst exhibited a higher SCR activity than Mn/Al–SBA-15 or Fe/Al–SBA-15 due to a synergistic effect between Mn and Fe. After the addition of Fe, the binding energy of Mn 2p_3/2 on Mn–Fe/Al–SBA-15(573) decreased by about 0.4 eV and the Mn^4 +/Mn^3 + ratio decreased to 1.10. The appropriate Mn^4 +/Mn^3 + ratio may have a great effect on the reduction of NO over Mn–Fe/Al–SBA-15(573) catalyst.     

Thermal and hydrothermal stability of amino-functionalized SBA-16 and promotion of hydrophobicity by silylation

Amino-functionalized SBA-16 were prepared by silylating various N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AEAPS) contents on the SBA-16 supports, and their hydrophobicity, thermal and hydrothermal stabilities were investigated with water adsorption isotherms, temperature-programmed-degradation mass spectrometry (TPD-MS) and N₂ adsorption–desorption. The functionalized SBA-16 samples show super hydrophobicity to the SBA-16 support, due to the coverage of silanol groups by amino-groups. The amino-groups silylated on SBA-16 are thermally stable up to 200 °C both in He and in air. Decomposition in He and combustion of the amino-groups in air were observed at higher temperature (beyond 200 °C), respectively. The functionalized SBA-16 samples show high hydrothermal stability and they are related to the extent of silylation.     

Synthesis and characterization of the SBA-15/carbon cryogel nanocomposites

The ordered mesoporous silica SBA-15 materials were synthesized using Pluronic P123 (non-ionic triblock copolymer, EO₂₀PO₇₀O₂₀), under acidic conditions. SBA-15/carbon cryogel composites were obtained by sol–gel polycondensation of resorcinol and formaldehyde followed by freeze drying, and subsequent pyrolysis, in the presence of different amounts of SBA-15. For comparison purpose, SBA-15/carbon composite was also prepared using sucrose as carbon source. These materials were characterized by room temperature nitrogen adsorption–desorption measurement, X-ray diffraction, scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy. It was revealed that the samples have amorphous structure, high specific surface area (350–520 m² g^?1) and developed meso- as well as microporosity. The porosity of structure depends on the carbon source and Si/C ratio which can be easily controlled by varying concentration of starting solution.     

Novel low-κ polyimide/mesoporous silica composite films: Preparation,microstructure, and properties

A series of novel low-dielectric constant (low-κ) polyimide (PI) composite films containing the SBA-15 or the SBA-16-type mesoporous silica were successfully prepared via in situ polymerization and following thermal imidization. Their morphologies, dielectric constants, and thermal and dynamic mechanical properties were investigated. It is found that the dielectric constants of the composite films can be reduced from 3.34 of the pure PI to 2.73 and 2.61 by incorporating 3 wt% SBA-15 and 7 wt% SBA-16, respectively. The reduction of the dielectric constant is attributed to the incorporation of the air voids (κ = 1) stored within the mesoporous silica materials, the air volume existing in the gaps on the interfaces between the mesoporous silica and the PI matrix, and the free volume created by introducing large-sized domains. The PI/mesoporous silica composite films prepared in this study also present stable dielectric constants across the wide frequency range and a good phase interconnection. The improvement of the thermal stability and dynamic mechanical properties of the PI film is achieved by incorporation of the mesoporous silica materials. The enhanced interfacial interaction between the surface-treated mesoporous silica and the PI matrix has led to the minimization of the deterioration of the mechanical properties. The incorporation of the mesoporous silica materials is a promising approach to prepare the low-κ PI films.     

Production of high-quality biodiesel fuels from various vegetable oils over Ti-incorporated SBA-15 mesoporous silica

Ti-incorporated SBA-15 mesoporous silica (shortly termed Ti-SBA-15) was a highly efficient and recyclable solid acid to synthesize high-quality biodiesel fuel (BDF) derived from various vegetable oils at moderate reaction condition, in comparison to siliceous SBA-15 and commercial TiO₂ catalysts with different anatase sizes, where the catalytically active sites mainly related to the tetrahedral-coordinated Ti(IV) species with weak Lewis acid nature. The TOF values of Ti-SBA-15 catalysts were around 18–166 h^− 1, an order of magnitude larger than those of commercial TiO₂ catalysts. A high-quality BDF containing more than 98.4 mass% of fatty acid methyl ester (FAME), which met with international fuel standard, was obtained over 3Ti-SBA-15 catalyst at 200 °C using a methanol/oil ratio of 108. Most importantly, the 3Ti-SBA-15 catalyst showed extremely high water and free fatty acid (FFA) tolerance levels, which were several ten times better than homogeneous and heterogeneous catalysts in conventional BDF production technology.     

In situ hydrothermally synthesized mesoporous LaCoO3/SBA-15 catalysts: High activity for the complete oxidation of toluene and ethyl acetate

Mesoporous yLaCoO₃/SBA-15 (y = 10–50 wt%) catalysts were prepared and characterized for the combustion of toluene and ethyl acetate (EA). The results show that well-ordered mesoporous LaCoO₃/SBA-15 catalysts of high surface areas (338–567 m²/g) could be fabricated by a facile in situ method of hydrothermal treatment. The particles of perovskite-type LaCoO₃ were highly dispersed on the walls of pore channels. The ordered mesoporous structure and high dispersion of LaCoO₃ are beneficial to the adsorption and activation of toluene and EA molecules. We found that in terms of specific activity, the in situ fabricated 35LaCoO₃/SBA-15 and 40LaCoO₃/SBA-15 is, respectively, superior to 35LaCoO₃/SBA-15_imp (generated by incipient wetness impregnation method) and bulk LaCoO₃ (prepared by sol–gel method) in catalytic performance. Based on the above results, we conclude that the excellent performance can be attributed to the good dispersion of highly reducible LaCoO₃ species in yLaCoO₃/SBA-15.     

Synthesis of pure rod-like α-Si3N4 powder with in situ C/SBA-15 composite

Well crystallized pure rod-like α-Si₃N₄ powder (PRSN) without β-Si₃N₄ was successfully synthesized by carbothermal reduction-nitridation (CRN). In situ carbon/mesoporous silica composite (C/SBA-15) was used as a new kind of raw material. Due to in situ composited carbon, the CRN temperature was decreased and the phase transition from α to β-Si₃N₄ was hindered. The sintering temperature was lowered to 1380 °C and the soaking time of the optimal synthesis condition was reduced to 6 h. Moreover, the as-synthesized rod-like α-Si₃N₄, which is induced by SBA-15, was used to enhance the fracture toughness (K_Ic) of α-Si₃N₄ based ceramics, which was sintered by spark plasma sintering (SPS). Compared with the undoped ceramics (2.9 MPa m^1/2), α-Si₃N₄ ceramics doped with 10 vol% PRSN exhibited a higher K_Ic value (4.9 MPa m^1/2), and lower dielectric loss in MHz frequency range. The results demonstrated that the PRSN powder would be promising for toughening α-Si₃N₄ based ceramics.     

Mechanism of NO reduction by CO over Pt/SBA-15

The mechanism of the CO + NO reaction catalyzed by Pt/SBA-15 was studied via independent investigations of CO oxidation and NO disproportionation. Below 400 °C, both CO + O₂ and CO + NO reactions approach 100 % conversion, while the catalyst shows negligible activity for NO disproportionation. These results suggest that CO oxidation by atomic oxygen arising from NO dissociation is not a major route for CO₂ formation in the CO + NO reaction. In situ IR spectra reveal the formation of isocyanates (NCO⁻) adsorbed on silica. Their surface concentration changes with the extent of the CO + NO reaction. A mechanism is proposed in which isocyanates are reaction intermediates.     

Thermolytic conversion of a bis(alkoxy)tris(siloxy)tantalum(V) single-source molecular precursor to catalytic tantala–silica materials

The new complex (ⁱPrO)₂Ta[OSi(O ^tBu)₃]₃ (1) was prepared via silanolysis of Ta(O ⁱPr)₅ with (^tBuO)₃SiOH and is a useful structural and spectroscopic (NMR, FTIR) model of Ta(V) on silica. The complex was also used to prepare tantalum-containing silica materials, via the thermolytic molecular precursor method (yielding Ta₂O₅ ⋅ 6SiO₂ and Ta₂O₅ ⋅ 18SiO₂) or by grafting 1 onto mesoporous SBA-15 silica (yielding a surface-supported tantala species, TaSBA-15). The solution phase thermolysis of 1 in nonpolar media afforded homogeneous, high-surface-area (ca. 450 m² g⁻¹) xerogels (Ta₂O₅ ⋅ 6SiO₂) that are amorphous up to approximately 1100 °C. A more silica-rich tantala–silica material (Ta₂O₅ ⋅ 18SiO₂) was prepared via a solution-phase co-thermolytic route with 1 and HOSi(O ^tBu)₃, to yield a material with a Si/Ta ratio of 9/1. It was demonstrated that tantala–silica materials are active as catalysts for cyclohexene oxidation.     

Mesoporous silicas containing carboxylic acid: Preparation,thermal degradation,and catalytic performance

The calcination and thermal degradation behaviors of surfactants in mesoporous silicas SBA-15 and MCM-41 were investigated by FT-IR, ¹³C CP/MAS NMR, TG/DTA, and GPC. It was found that carboxylic acid-containing products were generated as active components in the mesopores of SBA-15 and MCM-41 from the triblock copolymer (PEO)₂₀(PPO)₇₀(PEO)₂₀ and cetyltrimethylammonium bromide (CTAB), respectively; the latter materials were used as templates. The carboxylic acid-containing mesoporous silica obtained showed a catalytic activity for hydrolysis of sucrose. The acidity was evaluated by means of NaOH titration. The acidity sensitively depended on both the calcination temperature and the atmosphere; the maximum appeared at 150 °C in air for SBA-15 where the highest activity was observed. However, the product in MCM-41 showed a lower catalytic activity than that in SBA-15. The SBA-15 product was easily leached from the mesopores of SBA-15 into the solution, but the degree of leaching for MCM-41 was considerably smaller than that for SBA-15.     

Ni based on dual-support Mg-Al mixed oxides and SBA-15 catalysts for dry reforming of methane

A series of new dual support Ni catalysts consisting of Mg-Al mixed oxides and SBA-15 was prepared. The performance of the catalysts in the dry reforming of methane to syngas was investigated at 800 °C, atmospheric pressure and gas hourly space velocity of 12000 mL/g_cat · h. The ordered hexagonal mesoporous structure of SBA-15 coated with Mg-Al mixed oxides was found to be maintained. One of the composite catalysts exhibited excellent anti-deposition of carbon and high stability for 500 h on stream. It is concluded that strong metal-support interaction promoted catalyst performance by inhibiting carbon deposition and metal sintering.     

Regenerable solid CO2 sorbents prepared by supercritical grafting of aminoalkoxysilane into low-cost mesoporous silica

The present work examines the functionalization of silica supports via supercritical CO₂ grafting of aminosilanes, which is an important step in the preparation of materials used as solid sorbents in CO₂ capture. Four materials have been considered as solid supports: two commercially available silica gels (4.1 and 8.8 nm pore diameter), the mesoporous silica MCM-41 (3.8 nm pore diameter) and a microporous faujasite of the Y type. Mono- and di-aminotrialkoxysilane were chosen for this study. The optimal operating conditions required to have free aminosilane in solution were first evaluated by studying the phase behavior of the system scCO₂/aminosilane at different pressures and temperatures. FTIR spectroscopy was used to determine the chemical structure of the grafted species. Aminosilane uptake was estimated by thermogravimetric and elemental analysis. Densities up to 3–4 molecules of monoaminosilane per nm⁻² were reached by using a small amount of a cosolvent together with the supercritical CO₂. The samples were characterized in regards of thermal stability, showing that aminosilane groups were covalently attached to the amorphous silica surface in the mesoporous supports, but not in the microporous zeolite. Low temperature N₂ and ambient temperature CO₂ isotherms were recorded to establish the adsorptive behavior of the prepared hybrid materials. The amine functionalized MCM-41 and the 8.8 nm silica gel exhibited a significant higher uptake of CO₂ at low pressures compared with the bare supports. On the contrary, for the 4 nm silica gel and the zeolite the adsorption decreased after impregnation.     

Diluent filler particle size effect for thermal stability of epoxy type resin

Epoxy resin is used as a material for electrical and electronics molding in various forms but its thermal conductivity must be controlled with various additives on account of its lower conductivity than metal or ceramics. Silicon dioxide (SiO₂) and silica were selected as the reinforcement and diluent filler for epoxy resins, respectively. The optimum amount of reinforcement filler, SiO₂, was 50 wt%. The thermal properties and thermal stability were observed according to silica ratio and particle size. An epoxy modified with a polyamide type hardener showed superior thermal conductivity to that modified with a cyclo-aliphatic amine type hardener. The thermal conductivity increased with increasing silica ratio and particle size. The thermal stability evaluation based on the particle size of silica was in the order of 14/18 mesh (1.00–1.16 mm) > 8/10 mesh (1.65–2.36 mm) > 28/35 mesh (0.42–0.59 mm). The optimum silica size of the diluent filler was 14/18 mesh (1.00–1.16 mm). An epoxy type resin transformer with excellent thermal properties and thermal stability could be designed when the mixing weight of epoxy resin was equal to that of the hardener.     

Potassium-modified molybdenum-containing SBA-15 catalysts for highly efficient production of acetaldehyde and ethylene by the selective oxidation of ethane

Mo-incorporated SBA-15 (Mo-SBA-15) catalysts with different Mo:Si molar ratios were synthesized by a direct hydrothermal method, and SBA-15-supported Mo catalysts (Mo/SBA-15 and K-Mo/SBA-15) were prepared by an incipient-wetness impregnation method. The structures of the catalysts were characterized by means of N₂ adsorption–desorption, XRD, TEM, FT-IR, and UV-Raman, and their catalytic performance for the oxidation of ethane was tested. Turnover frequency and product selectivity are strongly dependent on the molybdenum content and catalyst preparation method. Furthermore, the addition of potassium promotes the formation of isolated tetra-coordination molybdenum species and potassium molybdate. The K/Mo-SBA-15 catalysts possess much higher catalytic selectivity to acetaldehyde in the selective oxidation of ethane than the supported molybdenum catalysts (Mo/SBA-15 or K-Mo/SBA-15). The highest selectivity of CH₃CHO + C₂H₄ 68.3% is obtained over the K/Mo-SBA-15 catalyst. Analysis of kinetic results supports the conclusion that ethane oxidation is the first-order reaction and ethane activation may be the rate-determining step for the oxidation of ethane. Ethylene is a possible intermediate for acetaldehyde formation.     

Suprarmolecular hydrogels driven by the dual host–guest interactions between α-cyclodextrin and ferrocene-modified poly(ethylene glycol) with low-molecular-weight

In general, α-cyclodextrin (α-CD) and low-molecular weight poly(ethylene glycol) (low-MW PEG) (M_w = 400–10,000) cannot construct supramolecular hydrogels but easily form crystalline precipitates. In this study, low-MW PEG (M_n = 2000, PEG-2000) was functionalized by ferrocene as mono-end-group. The obtained ferrocene-modified PEG-2000 (FcPEG-2000) further self-assembled into supramolecular hydrogel with α-CD even at low concentration (C_FcPEG-2000 = 17 mg/ml), driven by dual host–guest interaction between α-CD and FcPEG-2000. Interestingly, the hydrogel was still observed even when hydrophobic Fc group was oxidized to hydrophilic ferrocenium (Fc⁺) or included into the cavity of β-CD. In the former case, the existence of Fc⁺ end groups is considered to decrease the probability of PEG de-penetration from α-CD cavity, so that α-CDs have more location and opportunities to aggregate into more channel-type crystalline domains as physical cross-linking points. While in the later case, the synergistic effect of host–guest interaction between β-CD and ferrocenyl groups and host–guest interaction between α-CD and PEG chains are considered to be the main reason. The resultant FcPEG-2000 based hydrogels showed the property of shear-thinning.