Gold nanoparticles stabilized in a novel periodic mesoporous organosilica of SBA-15 for styrene epoxidation

The stabilization of gold nanoparticles (GNPs) by disulfide groups linked to imidazolium chloride units in a periodic mesoporous organosilica of SBA-15 and their catalytic performances in the epoxidation of styrene were investigated. The mesoporous organosilica (PMO-SBA-15) was synthesized via a one-pot condensation process involving the assembly of ionic liquid silsesquioxane organic precursor containing disulfide group and tetraethoxysilane (TEOS) in the presence of P123 (EO₂₀PO₇₀EO₂₀). Aqueous chloroaurate ions were in situ reduced by the silanol groups presented on the channel surface of the mesoporous organosilica to form GNPs that were subsequently captured by disulfide group to obtain Au-containing mesoporous organosilica (Au-PMO-SBA-15). The PMO-SBA-15 and Au-PMO-SBA-15 were characterized by XRD, ²⁹Si MAS-NMR, FT-IR, UV–vis, TEM and N₂ adsorption–desorption measurements. It was found that both PMO-SBA-15 and Au-PMO-SBA-15 had the typical characteristics of mesoporous SBA-15, and that the GNPs entrapped into the channels of Au-PMO-SBA-15 possessed mean size of ca. 1.8 nm. The Au-PMO-SBA-15 was used as a catalyst in the epoxidation of styrene. 95% of styrene conversion and 75% of selectivity to styrene epoxide were obtained over the novel Au-PMO-SBA-15 catalyst, which were higher than that over the reported nano-Au catalysts. Furthermore, the Au-PMO-SBA-15 could be conveniently recovered for recycled use without significant loss of catalytic activity and selectivity.     

Direct synthesis and catalytic performance of ultralarge pore GaSBA-15 mesoporous molecular sieves with high gallium content

Mesoporous GaSBA-15 molecular sieves with different n_Si/n_Ga ratios have been directly synthesized using Pluronic 123 triblock polymer as a structure-directing agent by pH-adjusting method. The mesoporous materials have been characterized using ICP-AES, XRD, N₂ adsorption, ⁷¹Ga-MAS NMR, SEM and TEM. ICP-AES studies show a high amount of gallium incorporation on the silica pore walls. The structural and textural properties of calcined GaSBA-15 are characterized by XRD and N₂ adsorption. ⁷¹Ga MAS NMR results demonstrate that a high amount of tetrahedral-gallium could be substituted for Si in the framework of SBA-15. TEM and FE-SEM images show the uniform pore diameter and rope-like hexagonal mesoporous structure of GaSBA-15. These GaSBA-15 materials have been used as catalysts for vapour-phase t-butylation of 1,2-dihydroxybenzene (DHB) for selective synthesis of 4-t-butylcatechol (4-TBC) under different reaction conditions. GaSBA-15(10) gave the highest 93.2% conversion of DHB and 95.7% selectivity of 4-TBC as compared with other GaSBA-15 catalysts.     

Benzylation of benzene and other aromatics by benzyl chloride over mesoporous AlSBA-15 catalysts

Aluminum-containing mesoporous molecular sieves AlSBA-15 with different n_Si/n_Al ratios and AlMCM-41 have been synthesized hydrothermally and characterized in detail by physicochemical methods, viz. XRD, N₂ adsorption and ²⁷Al NMR spectroscopy. The low angle XRD and N₂ adsorption measurements reveal that the structural order of SBA-15 was retained after the incorporation of Al. The increase of the unit cell parameter with increasing aluminum content and ²⁷Al MAS NMR spectroscopy confirm the incorporation of aluminum in the framework. Benzylation of benzene and substituted benzenes reaction employing benzyl chloride as the alkylating agent over AlSBA-15 and AlMCM-41 have been investigated. The influence of various reaction parameters such as reaction temperature, reactant feed ratio and catalyst amount affecting the activity and selectivity of AlSBA-15, have been studied. Among the mesoporous catalysts studied, AlSBA-15(45), where the number in parentheses indicates the molar n_Si/n_Al ratio, shows both high conversion and high selectivity for the benzylation of benzene. The activity of this catalyst for the benzylation of different aromatic compounds is in the following order: benzene > toluene > p-xylene > mesitylene > anisole. Kinetics of the benzene benzylation over different catalysts have also been investigated.     

Synthesis of hexagonal and cubic mesoporous silica using power plant bottom ash

An alkali fusion method was adopted to extract silicate species from coal bottom ash in a power plant and the supernatant solution was used for the synthesis of MCM-41, SBA-15, and SBA-16 mesoporous silica materials. The minor impurities present in the bottom ash were not found to be detrimental to the successful formation of mesoporous silica phases. Additional silica from sodium metasilicate was introduced to improve the textural properties for SBA-15 and SBA-16. According to SEM analyses, particle morphology of the samples gradually approaches those prepared using pure chemical as the amount of external silica source increases. XRD analyses confirmed well-ordered mesostructures in all of these silica materials. N₂ adsorption–desorption isotherms of MCM-41 prepared using bottom ash showed a type IV isotherm with a region of steep increase due to capillary condensation, whilst SBA-15 and SBA-16 showed type IV isotherm with H1 and H2 hysteresis loops, respectively. ²⁷Al MAS NMR analysis of MCM-41 synthesized from the supernatant solution reveals that the extracted Al species from bottom ash were tetrahedrally incorporated in the framework. TEM clearly showed the uniform pore structure of the materials prepared using the industrial waste.     

Ordered mesoporous aluminosilicates with very low Si/Al ratio and stable tetrahedral aluminum sites for catalysis

New and ordered 2D-hexagonal (p6mm) mesoporous aluminosilicates (CMI-11) have been synthesized in strongly alkaline media using aluminosilicate ester ((Bu^sO)₂-Al-O-Si-(OEt)₃) as single-source molecular precursor and CTMABr as surfactant and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N₂ adsorption–desorption and ²⁷Al and ²⁹Si MAS NMR spectroscopy. These mesoproous aluminosilicates exhibit a very low Si/Al ratio of 1.9 and highly thermal stable tetrahedral aluminum sites in the mesoporous walls. ²⁷Al and ²⁹Si MAS NMR spectroscopy indicates that the pore walls of CMI-11 are fully condensed with molecular homogeneity of Si–O–Al linkage. These materials are highly important in catalysis, in particular for the petroleum processing and the bulky molecules treatment.     

Characterization of Pt/SBA-15 prepared by the deposition–precipitation method

Mesoporous silica SBA-15 was prepared and loaded with Pt using the deposition–precipitation method (DP). The Pt loaded material was characterized by N₂ sorption, and X-ray diffraction (XRD) at low scattering angles as well as XRD at wide angles, in order to monitor the impact of the metal deposition pathway on the mesoporous texture. After DP the material contains ordered mesoporous silica as well as a fraction appearing as non-ordered amorphous silica. This is most likely caused by the hydrothermal treatment involved in the DP. The material was also characterized using NIR and ²⁹Si MAS NMR spectroscopy. The NIR results of the calcined materials indicate that the silanol groups of SBA-15 may act as anchoring groups for the metallic Pt particles. The NMR spectroscopy data shows that the Pt/SBA-15 sample prepared by the DP method posseses a better short-range regularity of SBA-15 walls as compared to the parent SBA-15. This is suggested to be caused by dissolution and possible re-precipitation of siliceous species.     

Use of mesoporous SBA-15 for nanostructuring titania for photocatalytic applications

SBA15–TiO₂ samples prepared by introducing titanium with a grafting method and having TiO₂ loadings below 15 wt.% have been characterized by XRF, XRD, IR, porosimetry, SEM, HRTEM, and UV–Visible diffuse reflectance. Differently from the samples reported in the literature characterized by a high TiO₂ loading, no evidences have been found for the presence of titania particles inside or outside the mesopores of SBA-15. Three different titanium species were instead evidenced to be present. The first two derive from the reaction of titanium with silanol groups in the corona area of inner SBA-15 walls leading to the formation of either TiO₄ tetrahedral sites (by reaction by hydroxyl nests of surface defect sites) and/or pseudo-octahedral surface sites anchored by two (or more) Si or Ti ions through bridging oxygens. The third species derives from the reaction of titanium in the regions with high sylanol density, e.g. in the micropores located in the corona of SBA-15 channels, leading to the formation of TiO₂-like nanoareas (probably Si-doped) with dimensions of around 1–2 nm maximum. The potential interest of these materials as photocatalysts, for the presence of a TiO₂-like nanoareas highly accessible by reactants, is discussed.     

介孔氧化硅固载Yb(OTf)3的制备及催化葡萄糖生产乳酸

采用溶剂法和焙烧法制备了SBA-15和MCM-41两类介孔氧化硅,并以此为载体制备固载型三氟甲基磺酸镱(Yb(OTf)₃)催化剂。通过小角X射线衍射(SAXD)、氮气吸附/脱附、²⁹Si固体核磁共振光谱(NMR)、透射电子显微镜(TEM)及热重分析(TG)等方法对载体及催化剂进行表征,研究其在葡萄糖制备乳酸反应中的催化性能。结果表明：溶剂法制备的氧化硅表面羟基含量比焙烧法高,负载的磺酸基团和三氟甲基磺酸镱都更多,催化活性更高;SBA-15的平均孔径比MCM-41的大3 nm左右,这使得SBA-15具有更好的传质性能以及Yb(OTf)₂-SBA-15具有更好的催化性能。以Yb(OTf)₂-SBA-15-S为催化剂,在2 MPa N₂压力、190 ℃下反应60 min,乳酸的收率达到42.35%。     

过氧化氢溶液中痕量离子吸附分离用氨基功能化SBA-15的制备及性能

通过后接枝法制备了氨基功能化SBA-15介孔氧化硅(S-N),用于吸附过氧化氢溶液中的金属和阴离子及有机杂质制高纯过氧化氢.研究了接枝量对吸附剂结构和性能的影响并发现S-N中的氮含量随接枝剂用量增加而增加,最高为1.83％.S-N保留了高度有序的六方孔道结构,但比表面积和孔体积均随接枝量增加而下降.在过氧化氢溶液中,各...     

Synthesis,characterization of triphenyltin grafted on SBA-15 mesoporous silica and its catalytic performance for the synthesis of 4-methylacetophenone

The production of Ph3Sn–O–SBA-15 (Ph3SnSBA) was achieved by heating triphenyltin chloride and SBA-15 in N-methylpyrrolidone at 190 °C for 5 h using triethylamine as a catalyst. The composition, structure, and sur-face physical and chemical properties of Ph3SnSBA were characterized using inductively coupled plasma-atomic emission spectroscopy (ICP-AES), 13C, 119Sn and 29Si solid-state nuclear magnetic resonance (NMR) spectroscopy in situ pyridine infrared spectroscopy (Py-IR), N2 adsorption–desorption isotherms, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results of ICP-AES and organic elemental analysis showed that the grafting yield of Sn was 17%(by mass) for Ph3SnSBA. The elemental analysis and solid-state NMR results for Ph3SnSBA were consistent with grafting of triphenyltin on SBA-15. The N2 adsorption–desorption, XRD and TEM analyses showed that Ph3SnSBA retained an ordered hexagonal mesoporous structure, resulting in decreases in the surface area, pore size and mesopore volume, and an increase in acidity as compared with SBA-15. The Hammett acidity function (H0) value and the number of acid sites for Ph3SnSBA, obtained by the Hammett methods, were 2.77–3.30 and 2.07 mmol·g?1, respectively. The Friedel–Crafts acylation of toluene and acetic anhydride over Ph3SnSBA was investigated. The yield of methylacetophenone (MAP) and the selectivity for 4-methylacetophenone (PMAP) were 79.56%and 97.12%, respectively, when the conditions were n (toluene):n (anhydride)=2.0:1.0 with 6%(by mass) catalyst, and heating under reflux for 5 h. The PMAP selectivity stil reached 93.11%when Ph3SnSBA was used for the fifth time under the same reaction conditions.     

Synthesis, characterization and catalytic application of mesoporous molecular sieves SBA-15 functionalized with phosphoric acid

The phosphoric acid groups has been successfully grafted on the surface of mesoporous molecular sieve SBA-15 to form a solid acid catalyst P-SBA-15 by post-synthesis method. The samples were characterized by means of XRD, FT-IR, SEM, TEM, ³¹P MAS NMR, NH₃-TPD, N₂ adsorption/desorption and the esterification reaction. The XRD and N₂ adsorption/desorption results indicate that P-SBA-15 catalyst keeps the 2D hexagonal mesoporous structure and opens channels with the lower surface area of 554.35?m²/g compared with that of SBA-15. The SEM and TEM results show that the figuration of P-SBA-15 behaves ??rod-like?? and phosphoric acid groups is scattered differently on the surface of P-SBA-15. The FT-IR and ³¹P MAS NMR results display that phosphorus species graft onto the surface of SBA-15, which provide the Br?nsted acid sites on the surface of P-SBA-15. The acidity of the generated Br?nsted acid sites on P-SBA-15 significantly is verified by NH₃-TPD. The esterification reaction results shows that catalytic activity of P-SBA-15 is enhanced significantly compared with that of SBA-15, and its stability is good.     

Highly Sensitive Fluorescence Probe Based on Functional SBA-15 for Selective Detection of Hg<Superscript>2+</Superscript>

An inorganic–organic hybrid fluorescence chemosensor (DA/SBA-15) was prepared by covalent immobilization of a dansylamide derivative into the channels of mesoporous silica material SBA-15 via (3-aminopropyl)triethoxysilane (APTES) groups. The primary hexagonally ordered mesoporous structure of SBA-15 was preserved after the grafting procedure. Fluorescence characterization shows that the obtained inorganic–organic hybrid composite is highly selective and sensitive to Hg²⁺ detection, suggesting the possibility for real-time qualitative or quantitative detection of Hg²⁺ and the convenience for potential application in toxicology and environmental science.     

Dendritic SBA-15 supported Wilkinson's catalyst for hydroformylation of styrene

After PAMAM (polyamidoamine) dendrimers have been successfully grown in SBA-15 mesoporous materials, Wilkinson's catalyst (RhCl(PPh₃)₃) precursor has been tethered on these dendritic supports to produce heterogeneous catalysts for hydroformylation reaction of styrene. SBA-15 has been functionalized by two methods. In the passivation method, the silanols outside the SBA-15 pores have been passivated to preclude the rhodium precursor to be tethered outside the channels. The rhodium catalysts supported in the pore channels of this passivated SBA-15 show positive dendritic effects in enhancing the catalytic activity, regio-selectivity and stability of the catalyst by minimizing the leaching of the rhodium complex catalyst from the catalyst support to the liquid-phase media.     

Incorporation of Ag nanostructures into channels of nitrided mesoporous silica

Nitrided mesoporous silica was used as a host for accommodating nano-silver into the channels. The nitridation of the mesoporous silica host, i.e. SBA-15, with ammonia caused the generation of –NH_x groups on the surface. The following impregnation of the nitrided SBA-15 with aqueous AgNO₃ solution and further reduction led to formation of silver nanostructures in the channels. The samples were characterized by FTIR, XRD, TEM and XPS techniques. The impregnation time has effect on the morphology of the resulting nanostructures. The interaction between silver species and surface –NH_x was the key to immobilize Ag in the channels. A scheme was proposed to illustrate the synthesis of Ag nanostructures using nitrided mesoporous host.     

Control of ordered structure and morphology of cubic mesoporous silica SBA-1 via direct synthesis of thiol-functionalization

Well-ordered cubic mesoporous silicas SBA-1 functionalized with thiol groups have been synthesized via co-condensation of tetraethoxysilane (TEOS) and 3-mercaptopropyltrimethoxysilane (MPTMS) templated by cetyltriethylammonium bromide (CTEABr) under strongly acidic conditions. Various synthesis parameters such as HCl concentration, synthesis temperature, and time for hydrothermal treatment were systematically investigated as a function of MPTMS contents. The materials thus obtained were characterized by a variety of techniques including powder X-ray diffraction (XRD), solid-state ¹³C and ²⁹Si NMR spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and nitrogen sorption measurements. Direct evidence of the presence of chemically attached thiol moieties was provided by solid-state ²⁹Si and ¹³C NMR spectroscopy. A high degree of structural ordering was still retained when MPTMS loading was incorporated up to 20 mol% in the synthesis mixture. Increasing the synthesis temperature and the time for the hydrothermal treatment not only increased the degree of framework cross-linking, but also did not lead to the undesirable phase transformation as often observed in the conventional synthesis of pure silica SBA-1. SEM results reveal that the morphology of thiol-functionalized SBA-1 depends on the HCl concentration used in the synthesis. The sample prepared with a low acid concentration exhibits a highly isotropic morphology with more facets than that of pure silica SBA-1, whereas it changes to a spherical shape as the acid concentration is increased. The maximum content of the attached thiol group (–SH) in the mesoporous framework is 2.39 mmol/g. The thiol-functionalized SBA-1 mesoporous materials are efficient Hg²⁺ adsorbents.     

Characterization of mesoporous alumina prepared by surface alumination of SBA-15

Mesoporous aluminas of controlled pore sizes were synthesized by multiple grafting of Al isopropoxide in organic solvents on mesoporous silica SBA-15. These materials were characterized by N₂ physisorption, TEM, XRD, ²⁷Al NMR and their surface chemical properties were probed by DRIFT, cumene cracking and MoO₃ thermal spreading. The results show that the chemical nature of the Al-grafted materials varies continuously with the number of grafting from pure silica to pure alumina. Typically, after three graftings, this original method of synthesis allows one to prepare ordered mesoporous aluminas with specific surface areas above 300 m² g⁻¹ and a narrow pore size distribution centered on ca. 60 Å. In addition to the characterizations, different models were developed to understand the evolution of the specific surface area and to discard a possible pore blocking.     

A comparative investigation on the properties of Cr-SBA-15 and CrOx/SBA-15

High-surface area and well-ordered mesoporous Cr-incorporated SBA-15 (Cr-SBA-15) and SBA-15-supported chromia (CrO_x/SBA-15) with Cr surface density = 0.05–1.11 Cr-atom/nm² have been prepared, respectively, using the one-step synthesis and incipient wetness impregnation method, and characterized by AAS, XRD, BET, ESEM, TEM, XPS, laser Raman, UV-Vis, FT-IR, and H₂-TPR. It is observed that the Cr-SBA-15 and CrO_x/SBA-15 samples showed an evolution of surface morphology from long chain-shaped to short rod-like and further to an irregularly spherical architecture at elevated Cr content, which might arise from the interaction of Cr ions or CrO_x domains with SBA-15. There were co-presence of tetrahedrally coordinated mono- and poly-chromate (Cr⁶⁺) as well as octahedrally coordinated Cr³⁺ species in Cr-SBA-15 and CrO_x/SBA-15, with the Cr⁶⁺ species being dominant at Cr surface density ≤0.22 Cr-atom/nm² in Cr-SBA-15 and Cr ≤0.54 Cr-atom/nm² in CrO_x/SBA-15, whereas the amount of the Cr³⁺ species increased markedly at Cr surface density ≥0.53 Cr-atom/nm² due to the formation of crystal Cr₂O₃ phase. Maximal Cr incorporation into Cr-SBA-15 and one monolayer surface CrO_x coverage on CrO_x/SBA-15 occurred at Cr surface density ≤0.53 Cr-atom/nm² and <1.11 Cr-atom/nm², respectively. The CrO_x/SBA-15 samples exhibited better reducibility than the Cr-SBA-15 samples, with the best reducibility exhibited at Cr surface densities of 0.54 and 0.12 Cr-atom/nm², respectively.     

Direct synthesis of highly ordered Co-SBA-15 mesoporous materials by the pH-adjusting approach

Cobalt-substituted SBA-15 (Co-SBA-15) mesoporous materials were directly synthesized under mild conditions (pH > 2.0) by a “pH-adjusting” method using sodium hydroxide. Characterization results, such as powder X-ray diffraction (XRD), N₂ physisorption and high-resolution transmission electron microscopy (HRTEM), showed that the resultant materials exhibit highly ordered hexagonal mesoporous structures, which was strongly correlated to the pH in the synthesis solution. The Co-SBA-15 sample obtained at pH of 3.0 gave the best structure. Solid state magic-angle-spinning nuclear magnetic resonance (MAS NMR) results indicated less condensation under higher pH. In addition, the pH also strongly affected the incorporation of cobalt cations in the silica framework. Diffuse reflectance UV–vis absorption spectra of calcined Co-SBA-15 samples and hydrogen temperature programmed reduction (H₂-TPR) demonstrated that the cobalt ions in the silica framework locate at tetrahedrally coordinated sites. The effect of pH and sodium (NaOH) addition on improving the cobalt ion incorporation and the mesostructure of Co-SBA-15 materials were also discussed.     

Synthesis and characterization of the layered sodium silicate ilerite

A sodium ilerite, molar ratios 1Na₂O:8.2SiO₂:10.2H₂O, was obtained with a good crystalline structure and characterized by several NMR techniques in addition to X-ray diffraction (XRD). The X-ray pattern of the as-synthesized ilerite is in very good agreement with the structure proposed by Gies and coworkers. The narrow ²⁹Si MAS NMR signals (FWHM=0.3 ppm) indicate a good short-range order of the framework. The proton dynamics influences several ²⁹Si NMR parameters. The 16 ppm signal in the ¹H MAS NMR spectra is explained by a proton in a bridging position in the short (2.3 Å) O4–O4 bonding. The quadrupole coupling constant C_qcc=100 kHz with η=0.2 for the 16 ppm signal, which was obtained from the ²H MAS NMR spectra, confirms this explanation. ¹⁷O NMR shows also a separate signal for SiOH groups but cannot resolve the three expected lines for SiOSi. PFG NMR detects a small mobile portion of water in the ilerite, which is located probably on the external surface of the crystallites. An intracrystalline diffusion coefficient of the intercalated water molecules of the order of magnitude 10⁻¹⁵ m² s⁻¹ was obtained by NMR tracer exchange experiments.     

Synthesis of hydrothermally stable aluminium-containing ethane-silica hybrid mesoporous materials using different aluminium sources

Aluminium-containing ethane-silica hybrid mesoporous materials having ethane groups in the frame wall positions are synthesized using aluminium isopropoxide as well as aluminium nitrate as the aluminium sources. The materials were characterized in detail using powder XRD, N₂ adsorption–desorption, SEM, TEM, TG-DTG, TPD, ²⁹Si, ¹³C and ²⁷Al MAS NMR techniques. Characterization techniques revealed that aluminium isopropoxide was the appropriate source for the synthesis of organo aluminosilicas on considering the structural ordering, acidity as well as the percentage of aluminium incorporation into the ethane bridge. ²⁷Al MAS NMR displays aluminium as tetrahedrally coordinated in both the aluminium-containing organosilicas. Unlike the conventional EtOH–HCl template extraction process, in the present studies, we had used EtOH–NH₄OH as the surfactant-extracting medium and chemical analysis results suggest that using this procedure the extent of dealumination can be greatly reduced. XRD and nitrogen physisorption studies further proved that the materials are hydrothermally stable, that the ordered pore channels retains its structure even after 150 h reflux in boiling water, while the conventional Al-MCM-41 catalyst collapsed its mesostructure after 50 h reflux in water. The improved hydrothermal stability of the hybrid materials, even in presence of sodium ions, is attributed to the thick pore walls as well as due to the presence of hydrophobic bridging ethane groups in the wall positions.