Low Energy TEM Characterizations of Ordered Mesoporous Silica-Based Nanocomposite Materials for Catalytic Applications (original) (raw)
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Chemistry - A European Journal, 2011
The influence of pore surface functionalities in mesoporous SBA-15 silica on the stability of a model olefin metathesis catalyst, namely Grubbs I, is substantiated. In particular, it is demonstrated that the nature of the interaction between the ruthenium complex and the surface is strongly depending on the presence of surface silanols. For this study, differently functionalized mesoporous SBA-15 silica materials were synthesized according to standard procedures and, subsequently, the Grubbs I catalyst was incorporated into these different host materials. All of the materials were thoroughly characterized by elemental analyses, nitrogen physisorption at-196 °C, thermogravimetric analyses, solid state NMR spectroscopy, and infrared spectroscopy (ATR-IR). By such in-depth characterization of the materials, it became possible to achieve models for the surface/catalyst interactions as a function of surface functionalities in SBA-15, e.g. in the case of purely siliceous silanol-rich SBA-15, octenyl-silane modified SBA-15, and silylated equivalents. It was evidenced that large portions of the chemisorbed species that are detected spectroscopically arise from interactions between the tricyclohexylphosphine and the surface silanols. A catalytic study using diethyldiallylmalonate in presence of the various functionalized silicas shows that the presence of surface silanols significantly decreases the longevity of the ring-closing metathesis catalyst, whereas the passivation of the surface by trimethylsilyl groups slows down the catalysis rate, but does not affect significantly the lifetime of the catalyst. This contribution thus provides new insights into the functionalization of SBA-15 materials and the role of surface interactions for the grafting of organometallic complexes.
Synthesis and characterization of SBA-3, SBA-15, and SBA-1 nanostructured catalytic materials
Journal of Colloid and Interface Science, 2007
A highly ordered large pore mesoporous silica molecular sieve SBA-3, SBA-15, Al-SBA-15, and SBA-1, were developed and characterized by XRD, BET, FTIR, SEM, and NMR-MAS. The catalytic materials were synthesized using different raw materials and operation conditions. These materials contain a regular arrangement of uniform channels with diameters between 1.8 and 10 nm, high specific surface area and high specific pore volume. The designed methods were effective for the synthesis, presenting each mesostructured materials, patterns of XRD and other characteristics corresponding to the reported ones in literature. The new route employed to synthesize Al-SBA-15, generates a catalyst with only aluminum in tetrahedral form, according to the data of 27 Al NMR-MAS. However, several reports indicated that the coordination of the Al atoms changes below the Si/Al ratio of 45, presenting peaks corresponding to penta and hexa-coordinated aluminum, which are absent in our samples (Si/Al = 50 and 33).
Microporous and Mesoporous Materials, 2009
Various methods proposed for preparing nanoparticles within porous matrices involve generally the impregnation of the matrix with a solution of precursors followed by reduction based on chemical, thermal, radiolytic, or photochemical process. In most cases, the amount of solution impregnated is small and not uniformly distributed in the matrix, with a yield less than 30% and concentrated around the matrix surface. We have developed a novel method for preparing composite materials, combining impregnation under partial vacuum with radiolytic reduction. This method has enabled us to obtain SBA-15 mesoporous silicas with 50-70% impregnation and to control the nanoparticle size.
Journal of Catalysis, 2009
The use of functionalized mesoporous silicas such as SBA-15 and MCM-41 as supports for Pd catalysis has become increasingly common, notably in important reactions such as the Suzuki-Miyaura reaction. However the analysis of the structural consequences of exposure to these harsh reaction conditions is not nearly as common. We report herein a study of the effect of the Suzuki-Miyaura reaction conditions on the mesoporous material, and on the catalytic activity of the resulting material. Although it has been determined that aqueous base is highly detrimental to the structure of the material, the boric acid produced during the actual coupling reaction has a significant protective effect on the material. This protective effect can be mimicked by the addition of exogenous boric acid to the reaction medium. The use of aluminum-doped material provides an additional protective effect that is not dependent on the presence of boric acid. Finally, we demonstrate conclusively that access to the pores is essential for catalysis, since loss of mesoporosity is coincident with loss of catalytic activity.
Synthesis and surface characterization of ordered mesoporous silica SBA-15
Ordered mesoporous silica SBA-15 materials were synthesized using Pluronic P123 (non-ionic triblock copolymer, EO 20 PO 70 O 20 ) as a template, under acidic conditions and different heating temperatures and time of the reaction solution. These materials were characterized by nitrogen adsorption-desorption measurements, Fourier-transformed infrared spectroscopy (FT-IR), and determination of points of zero charge and izoelectric points as well as particle diameters. Synthesis at lower temperature (80 • C) and longer time of reaction (48 h) gives samples with higher specific surface area (S BET = 710 m 2 g −1 ), mesoporose surface (S meso = 481 m 2 g −1 ) and narrower pore size distribution. Material synthesized at higher temperature (100 • C) and shorter time of reaction (24 h) has lower specific surface and mesoporosity (S BET = 641 m 2 g −1 and S meso = 367 m 2 g −1 ). At both samples, the presence of micropores was confirmed. The point of zero charge, pH PZC = 5.2 ± 0.2, and the isoelectric point, pH IEP = 2.3 ± 0.1, were not affected by synthesis conditions. Washing of silica samples in a dilute solution of nitric acid shifts the isoelectric point to a higher value (pH IEP = 3.0 ± 0.2) while the point of zero charge remains constant.
A study on the catalytic activity of a new acidic ordered mesoporous silica (SBA-15)
iranian journal of catalysis, 2018
SBA-15 is an interesting mesoporous silica material having highly ordered nanopores and a large surface area, which is widely employed as a catalyst. This mesoporous silica due to silanol groups is easily functionalized by various organic materials. A new acidic ordered functionalized mesoporous silica (SBA-15-Aminopropyl-Benzyl-SO3H) has been introduced as an efficient catalyst for solvent-free esterification of fatty acids with ethanol. The structure of the catalyst and prepared materials have been characterized by FT-IR spectroscopy, XRD, thermogravimetric analysis (TGA), TEM, acid-base titration and NH3-TPD techniques and N2 adsorption– desorption isotherm. The high loading acidic sites with hydrophobic nature of the catalyst facilitate the esterification reaction in high yield without using special methodology. The results demonstrated that the reaction can also be performed in water as an environmentally benign and inexpensive solvent. The catalyst has been easily separated fr...
SYNTHESIS AND CHARACTERIZATION OF SBA-15 AND Ti-SBA-15 NANOPOROUS MATERIALS FOR DME CATALYSTS
2012
Amorphous SiO 2 known as SBA-15 (Santa Barbara Amorphous) has been synthesized mixing consecutively water solutions of poly(ethylene glycol) C 3 H 6 O.C 2 H 4 O (P123), 2M HCl and tetraethoxysilan 98 % C 8 H 20 O 4 Si (TEOS) at 60 o C. The mixture has been dried at 100 o C and calcinated at 500 o C. The synthesized SBA-15 samples have been characterized by X-ray diffraction (XRD), FTIR spectroscopy, scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), and N 2 physisorption analysis. The Ti-SBA-15 has been prepared by impregnation using a solution of Ti-isoporopoxide in isopropanol with different concentrations (1, 5, 10, 15, 25 mass %). During the impregnation TiO 2 nanoparticles have been incorporated into the SBA-15 hexagonal channels. N 2-adsorption/desorption analysis has been carried out to investigate the specific surface area, pore size and pore diameter of Ti-SBA-15 to be used as a DME catalyst.
Journal of The American Chemical Society, 2006
A novel high surface area heterogeneous catalyst based on solution phase colloidal nanoparticle chemistry has been developed. Monodisperse platinum nanoparticles of 1.7-7.1 nm have been synthesized by alcohol reduction methods and incorporated into mesoporous SBA-15 silica during hydrothermal synthesis. Characterization of the Pt/SBA-15 catalysts suggests that Pt particles are located within the surfactant micelles during silica formation leading to their dispersion throughout the silica structure. After removal of the templating polymer from the nanoparticle surface, Pt particle sizes were determined from monolayer gas adsorption measurements. Infrared studies of CO adsorption revealed that CO exclusively adsorbs to atop sites and red-shifts as the particle size decreases suggesting surface roughness increases with decreasing particle size. Ethylene hydrogenation rates were invariant with particle size and consistent with a clean Pt surface. Ethane hydrogenolysis displayed significant structure sensitivity over the size range of 1-7 nm, while the apparent activation energy increased linearly up to a Pt particle size of ∼4 nm and then remained constant. The observed rate dependence with particle size is attributed to a higher reactivity of coordinatively unsaturated surface atoms in small particles compared to low-index surface atoms prevalent in large particles. The most reactive of these unsaturated surface atoms are responsible for ethane decomposition to surface carbon. The ability to design catalytic structures with tunable properties by rational synthetic methods is a major advance in the field of catalyst synthesis and for the development of accurate structure-function relationships in heterogeneous reaction kinetics.