介孔分子筛SBA-15表面改性对脂肪酶固定化的强化作用

引言 脂肪酶可以催化酯水解或醇解、酯合成、酯交换、多肽合成及高聚物合成等多种有机反应,已被广泛应用于食品、精细化工及制药工业中[1].作为重要的生物催化剂,脂肪酶应用的有效性和经济性很大程度上取决于酶的固定化.     

Silver nanoparticles synthesized from mesoporous Ag/SBA-15 composites

Silver nanoparticles were prepared by removing silica from mesoporous Ag/SBA-15 composites. The results of nitrogen adsorption–desorption isotherms, X-ray diffraction, transmission electron microscopy and UV–vis spectroscopy indicated that Ag nanoparticles existed in the pore channels of SBA-15. Ag nanoparticles with diameters in the range of 2.5–5.5 nm and a narrow size distribution were confirmed by atomic force microscope images and energy-dispersive X-ray spectroscopy. UV–vis spectroscopy showed a broad emission peak of Ag nanoparticles centered at ca. 438 nm.     

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.     

Selective oxidation of indole by chloroperoxidase immobilized on the mesoporous molecular sieve SBA-15

The selective oxidation of hydrocarbons is an important value-enhancing chemical transformation in particular with respect to fine chemicals and pharmaceuticals production. Enzymatic oxidations operate under mild reaction conditions and produce little if any waste. However, its industrial use is still limited mainly due to their high cost and the low space time yields. In the present work, chloroperoxiase from Calariomyces fumago immobilized on the mesoporous molecular sieve SBA-15 was applied for the oxidation of indole to 2-oxoindole using hydrogen peroxide or tert.-butyl hydroperoxide as oxidants. The performance of the immobilized enzyme was found to be superior to native chloroperoxidase with respect to maximum conversion and pH range applicable. However, immobilized CPO is still sensitive to high concentrations of hydrogen peroxide. The use of tert.-buty hydroperoxide is found to avoid this problem, but the reaction rate is significantly reduced.     

活性纳米金颗料在介孔分子筛SBA-15上的分散

Chemical modification （CM） and deposition-precipitation （DP） methods were used for the dispersion of active Au nanoparticles on mesoporous silica materials in this work. XRD, TEM, N2 adsorption isotherms and UV-Vis absorption spectra were used to characterize in detail Au-SBA-15 materials prepared by the two methods. The analysis results showed that high loading （1.7%, by mass） and uniform Au nanoparticles （approximately 3 nm） were dispersed in the channels of mesoporous SBA-15 by the CM method. While for the DP method, most of Au nanoparticles with the size of 10—15nm were aggregated outside of the channels of SBA-15 and the actual loading of Au was only 0.38% （by mass）.     

介孔分子筛SBA-15在催化领域的应用进展

从负载固体酸催化剂、金属和金属氧化物以及手性催化剂三方面综述了介孔分子筛SBA-15在催化领域应用的研究进展;并展望了介孔分子筛SBA-15在催化领域的研究方向。     

Tuning of nanostructured SBA-15 silica using phosphoric acid

A simple method is described to synthesize mesoporous SBA-15 with controlled distinct morphologies. Using the same initial synthesis mixture composition consisting of non-ionic P123 block co-polymer, tetra-ethyl orthosilicate as silica source and phosphoric acid, well-ordered mesoporous films, cakes, fibers and bundle-like structures were produced simply by changing the stirring rate. Free-standing films at the air–water interface and cake-like structures were obtained simultaneously under static conditions. On the other hand, fibers and bundles of threads resulted under vigorous and slow stirring conditions, respectively. Transmission electron microscopy (TEM) images of these bundles revealed straight parallel nanochannels oriented along the long axis of the bundles. X-ray fluorescence (XRF) measurements of the calcined samples indicated the presence of phosphorus, which might provide additional Brønsted acid sites for potential applications in catalysis.     

Immobilization of uranium in cristobalite ceramic through adsorption on mesoporous SBA-15 and further sintering process

The development of an adsorbent which can be easily transformed into stable ceramic waste forms through a simple route is necessary for the treatment of the radioactive wastewater. Herein, we report on the immobilization of uranium in cristobalite ceramic through adsorption on mesoporous SBA-15 and further sintering process. The mesoporous SBA-15 with short pore length was synthesized and employed to remove uranium from aqueous solution. Subsequently, the SBA-15 with adsorbed U (U/SBA-15) was solidified by sintering. The effects of sintering temperature and U content on the structure, densification and aqueous durability of the obtained cristobalite ceramic waste forms were investigated. The results indicate that the U/SBA-15 can be transformed into stable cristobalite ceramic after sintering at 1100–1400 °C for 6 h. Furthermore, all the obtained cristobalite ceramic waste forms exhibit good aqueous durability (∼10⁻⁴ g m^-2 d^-1). This work demonstrates a potential route and adsorbent to dispose the radioactive wastewater.     

Cu/SBA-15 as adsorbent for propane/propylene separation

Samples of mesoporous silica SBA-15 were prepared under hydrothermal conditions where Cu cations were incorporated to the structure by impregnation in order to compare the adsorption behavior in the presence and absence of this element. The adsorption/desorption equilibrium isotherms of propylene, propane, and N₂ were measured to evaluate their usefulness in the propane/propylene separation. All the adsorption isotherms of SBA-15 measured in the absence of Cu cations were described by the Freundlich equation, while the adsorption isotherms of propane on Cu/SBA-15 were better represented by the Henry equation and those of propylene were satisfactorily described by the Langmuir model in the range P < 100 Torr. The adsorption uptake of propylene increased and that of propane decreased in Cu/SBA-15 as compared to the amounts observed in the SBA-15 sample. The presence of Cu atoms in the adsorbent lattice increased the selectivity towards propylene. Under some working conditions the adsorbed amount of propylene in Cu/SBA-15 sample was totally reversible and the propane uptake, negligible.     

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.     

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.     

介孔分子筛SBA-15的改性研究进展

从金属改性、酸改性和氧化物改性三方面综述了介孔分子筛SBA-15的改性研究进展,重点介绍了SBA-15表面功能化后引入金属改性的方法。评述了金属纳米粒子的制备对改性的SBA-15催化剂催化性能的影响。     

Pore structure and graphitic surface nature of ordered mesoporous carbons probed by low-pressure nitrogen adsorption

Ordered mesoporous carbons (OMCs) were produced by pyrolysis of sucrose adsorbed in two different silica matrices (MCM-48 and SBA-15), followed by dissolution of the matrix in hydrofluoric acid. Subsequently, some of these OMCs were heat-treated at temperatures of up to 1600 °C. The OMC pore structure was studied by low-pressure nitrogen adsorption. Information on the graphitic order of the surface of the mesopore walls was also obtained from the nitrogen adsorption data. These results were correlated to the order of the graphene layers at the outer surface, which was studied by X-ray photoelectron spectroscopy (XPS).

The OMCs were predominantly mesoporous, but they also contained micropores. For OMCs produced in an SBA-15 matrix, the micropore volume decreased upon heating. After heating to 1600 °C, nearly all micropores had disappeared. Furthermore, upon heating the width of the mesopores increased from 35 to 50 Å. All these changes can be explained by a shrinking of the OMC framework upon heating. A different behavior was found for OMCs derived from MCM-48. Upon heating these materials at increasingly high temperatures, the width of the mesopores first decreased, and for temperatures above 1100 °C it increased again. For all OMCs studied the graphitic order of the mesopores and the order of the graphene layers at the outer surface increased upon heating. For a given temperature, the graphitic surface order of OMCs derived from SBA-15 and MCM-48 was similar.     

Synthesis of high surface area mesoporous silica SBA-15 for hydrogen storage application

In the present report, mesoporous silica SBA-15 was synthesized by different methods such as room temperature aging, hydrothermal, and sonication-mediated hydrothermal methods. The effect of different time and temperature on the synthesis method was investigated by conventional characterization techniques. The powders synthesized by different methods showed different properties, mainly in morphology and pore volume. In comparison to others, the powder synthesized by the hydrothermal method at 100°C for 48 hours showed exceptionally high surface area of 3274 m²/g. To date, as per our knowledge, no such value was reported in literature. Finally, the powders were characterized by H₂ storage capacity by the adsorption-desorption method using 99.999% H₂. The hydrogen adsorption capacity of the same powder was observed at 6.02 wt%. Also, this value seems to be the highest H₂ adsorption capacity in comparison to other powders described in literature.     

SBA-15 supports modified by Ti and Zr grafting for NiMo hydrodesulfurization catalysts

A series of Ti- and Zr-containing mesoporous SBA-15 supports and their respective NiMo catalysts were prepared to study the effect of the Ti and Zr loading into the support on the characteristics of Ni and Mo surface species and their catalytic activity in the 4,6-dimethyldibenzothiophene hydrodesulfurization (HDS). Ti and Zr-containing SBA-15 solids with different metal loading (up to 19 wt.% of TiO₂ or 22 wt.% of ZrO₂) were prepared by chemical grafting. The solids prepared were characterized by N₂ physisorption, X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (DRS), temperature-programmed reduction (TPR), chemical analysis and HRTEM. The results show that Ti- and Zr-SBA-15 supports with highly dispersed Ti and Zr species can be obtained without substantial loss of SBA-15 characteristics. Zr grafted species showed somewhat better dispersion on the SBA-15 surface than the corresponding Ti counterparts. It was found that TiO₂ and, especially, ZrO₂ incorporation in the SBA-15 support leads to stronger interaction of Mo and Ni species with the support providing better dispersion to the oxidic and sulfided metal species (XRD, TPR, HRTEM). NiMo catalysts supported on Ti- and Zr-containing SBA-15 showed high activity in 4,6-dimethyldibenzothiophene HDS. It can be concluded therefore that SBA-15 materials grafted with Ti or Zr species show promising features as supports for Mo-based hydrotreating catalysts.     

SBA-15的改性及催化文冠果油制备生物柴油

以介孔分子筛SBA-15为载体,采用直接合成法和后合成法镀饰Al后再负载碱金属盐KNO₃,制得负载型固体碱催化剂KNO₃-AlSBA-15和KNO₃-Al-SBA-15。用XRD、BET、SEM以及CO₂-TPD对催化剂进行表征。结果表明：在SBA-15上镀饰Al可以保护分子筛的介孔结构;进一步负载KNO₃,能够增强催化剂的碱性。将其应用于催化文冠果油酯交换制备生物柴油,结果显示催化剂KNO₃-Al-SBA-15的催化活性最好,优于传统均相催化剂,所得生物柴油产率可达92%,重复使用多次仍具有较好的催化效果。     

On the mechanical stability of mesoporous silica SBA-15

Mesoporous silica SBA-15 was synthesised at 80 °C. The calcined solids were exposed to a unilateral external pressure in the range 16–191 MPa in order to monitor the impact of the mechanical pressure on the properties of SBA-15. N₂ adsorption–desorption measurements, XRD and UV-Raman spectroscopy was used in order to evaluate the changes occurring in the SBA-15. For the XRD measurement, an internal Si standard was used to correct the position of the SBA-15 patterns. It appeared that the elevated pressure has no influence on the hexagonal cell parameter a. Through the N₂ sorption measurements the fraction of the preserved mesoporous structure was estimated to be 60% when the highest pressure has been used. As the remaining part of the material is irreversibly disintegrated into small particles, the pressed sample is considered to be heterogeneous. However, the preserved fraction is slightly modified, showing a smaller pore width and plugs located within the mesopores. The plugs most likely originate from a disintegrated fraction of the SBA-15. UV-Raman spectroscopy shows that the relative intensity of the band associated with the siliceous network (ω₁) has decreased on the pressed samples resulting in a less ordered material possessing an enhanced population of silanols as compared to parent SBA-15. We propose that the disorder introduced by pressing is responsible for the observed expansion of the SBA-15 walls, which is detected for the samples treated at higher pressures (112, 191 MPa).     

Synthesis and characterization of Co-containing SBA-15 catalysts

Two Co-SBA-15 catalysts were synthesized and characterized by thermogravimetry, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, porosity, UV–visible diffuse reflectance and temperature programmed reduction with H₂. The first catalyst was prepared synthesizing SBA-15 and then adding Co ions by impregnation (Co_imprSBA-15). The second catalyst was prepared using a more complex procedure of immobilization of cobalt ions in the presence of pyridine and H₂O₂ on –COOH groups anchored to the SBA-15 structure [Co-SBA-15(COOH)]. These COOH groups were created starting from cyano groups introduced during the synthesis of the periodic mesoporous materials as 4-triethoxysilylbutyronitrile. Characterization of the samples indicates that in both cases the typical 2D periodical hexagonal structure of SBA-15 was obtained, but with less ordered packing in the second case. The cobalt is highly dispersed in the SBA-15 (up to 9% w/w) and is present mainly as Co²⁺ ions in highly distorted tetrahedral or square pyramidal coordination. Some coordinatively unsaturated Co(II) Lewis acid centers are present in Co_imprSBA-15, while in Co-SBA-15(COOH) coordination of pyridine to cobalt tentatively may induce the formation of Co³⁺ ions, although in both catalysts the dominant species are Co²⁺ ions in a very close environment.     

Effect of pore structure of SBA-15 on immobilization of hemoglobin

Immobilization of hemoglobin (Hb) in SBA-15 with various pore sizes by physical adsorption was studied. The structure changes of mesoporous SBA-15 before and after the immobilization of Hb were characterized by N₂ adsorption isotherms, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Ultraviolet-visible spectroscopy (UV). The results indicate that SBA-15 is a good support for the immobilization of Hb due to its regular structure, large pore diameter, and high surface area. After immobilization of Hb, the regular structure of SBA-15 is still kept, but the pore diameter, pore volume and surface area decrease. With the increase of pore size, the binding amount and leaching amount of Hb increase. There is a maximum binding amount of Hb up to 355.2 mg/g _SBA-15 when pore size is 8.9 nm. It is suggested that the immobilization of Hb depends significantly on the pore size of SBA-15.     

Investigation of CuO/mesoporous SBA-15 sorbents for hot gas desulfurization

Metal oxides, are widely used as sorbents to remove H₂S from hot gases produced by gasification processes. These oxides, however, suffer from several problems such as low capacity, sintering, evaporation, low duration and mechanical strength. Pure metal oxides or their admixtures loaded on inert materials have been used to overcome these problems.