Structure and catalytic properties of Pd encapsulated in mesoporous silica SBA-15 fabricated by two-solvent strategy

The two-solvent method was employed to prepare Pd encapsulated in mesoporous silica (Pd/SBA-15). A 3.01 wt% Pd loading was achieved without the loss of pore ordering. Highly dispersed and uniform palladium nanoparticles could be detected using transmission electron microscopy confirming also the absence of large particles outside the mesopore silica. The catalytic activities of the Pd/SBA-15 nanocomposites were investigated in Heck coupling reactions with activated and non-activated aryl substrates. The Pd/SBA-15 nanocomposite exhibits excellent catalytic activities and reuse ability in air for the Heck carbon–carbon coupling reactions.     

Simple synthesis of mesoporous carbon with magnetic nanoparticles embedded in carbon rods

Magnetically separable ordered mesoporous carbon containing magnetic nanoparticles embedded in the carbon walls was synthesized using a simple synthetic procedure. The resulting magnetically separable mesoporous carbon was denoted as M-OMC (magnetically separable ordered mesoporous carbon) poly(pyrrole) with residual Fe²⁺ ions in the mesoporous channel was converted to carbon material containing superparamagnetic nanoparticles. The size of the magnetic nanoparticles obtained was restricted by the channel size of the SBA-15 silica template, which resulted in the generation of superparamagnetic nanoparticles embedded in the carbon rods. The blocking temperature of M-OMC is 110 K. Pore size and textural property of M-OMC is similar to that of hexagonally ordered mesoporous carbon fabricated using SBA-15 silica as a template. The saturation magnetization of M-OMC is ca. 30.0 emu/g at 300 K, high enough for magnetic separation.     

Geometrical confinement effect in the liquid-phase semihydrogenation of phenylacetylene over mesostructured silica supported Pd catalysts

Three types of mesostructured silica with different pore sizes (MCM-41, SBA-15, and MCF) were employed as supports for deposition of colloidal Pd nanoparticles obtained by the solvent reduction method. As determined by transmission electron microscopy (TEM), average Pd particle sizes on the various supports were quite similar and were not significantly different from the colloidal particles (~ 2.3–2.5 nm). There was limited access of the reactants to Pd active sites and suppression of CO chemisorption for the Pd/SBA-15, probably because most of the Pd particles were located inside the pores. This geometrical confinement effect in the case of Pd/SBA-15, however, resulted in an improved selectivity towards styrene at complete conversion of phenylacetylene. Such effect was similar to those reported in the literature for the Pd nanoparticles encapsulated in support matrices (simultaneous synthesis) and the presence of strong metal-support interaction effect in Pd/TiO₂.     

Highly accessible SnO2 nanoparticle embedded SBA-15 mesoporous silica as a superior photocatalyst

We address the accessibility of tin oxide (SnO₂) nanoparticles synthesized inside the pores of mesoporous silica (SBA-15) host. On using a low-temperature route for in situ synthesis of SnO₂ and hence eliminating interparticle aggregation, SnO₂ nanoparticles of diameter much smaller (3.5 nm) than the cylindrical pore diameter (6.3 nm) of the SBA-15 could be synthesized. This enables molecules diffusing into the SBA-15 pores to access the very high specific surface area of SnO₂; enabling the diffusing species to react easily with the latter. This is demonstrated by an enhanced photocatalytic degradation rate constant of an aqueous solution of rhodamine B dye, on contacting the latter with the SnO₂-SBA-15 composite.     

Preparation, Characterization and Catalytic Activity of Palladium Nanoparticles Encapsulated in SBA-15

A simple adsorption method was studied for the preparation of SBA-15-encapsulated palladium nanoparticles. This method employed the SBA-15 with organic template removed by ethanol extraction for the adsorption of cationic Pd precursors in alkaline solution followed by calcination and H₂ reduction. The pH of the solution was found to be a critical factor in determining the palladium content and the ordered mesoporous structure. Our characterizations revealed that the Pd nanoparticles prepared by this method were located inside the mesoporous channels and were quite uniform in size (mostly 3–4 nm). The SBA-15-encapsulated uniform Pd nanoparticles were efficient catalysts for solvent-free aerobic oxidation of alcohols.     

Preparation and characterization of CuO nanoparticles encapsulated in mesoporous Silica

CuO nanoparticles supported in mesoporous silica MCM-41 (or CuO-nano-MCM-41 nanocomposites) were prepared via an in situ method. A 2.10 wt.% Cu loading was achieved without the loss of pore ordering. Highly dispersed and uniform CuO nanoparticles could be detected using transmission electron microscopy (TEM) confirming also the absence of large particles outside the mesopore silica. The bandgaps of the resulting CuO particles are widened from 1.7 to 3.15 eV for an indirect allowed bandgap and from 3.25 to 4.43 eV for a direct allowed interband transition owing to the quantum size effect.     

In situ Formation of Palladium Nanoparticles Inside the Pore Channels of Ordered Mesoporous Silica

Palladium-containing SBA-15 (SBA-15-Pd) was synthesized via an in situ approach. In this procedure, molecular assembly template was employed as a hydrophobic carrier to provide the compatible environment for the hydrophobic compounds. The hydrophobic solvent (CHCl₃) was used as a transport medium to inject the Pd precursor (Pd(acetylacetonate)₂) directly into the inner core of the surfactant micelles. A 1.46 wt% Pd loading was achieved without the loss of pore ordering. Highly dispersed and uniform palladium nanoparticles could be detected using transmission electron microscopy confirming also the absence of large particles outside the mesopore silica. The catalytic activities of the SBA-15-Pd nanocomposites were investigated in Heck coupling reactions with activated and non-activated aryl substrates. The SBA-15-Pd nanocomposites exhibit excellent catalytic activities and reuse ability in air for the Heck carbon–carbon coupling reactions.     

Mesoporous silica synthesis: Energetics of interaction between framework and structure directing agent

The thermodynamics of mesoporous silicas (MCM-41, MCM-48, SBA-15, and SBA-16) were studied by solution calorimetry at 323 K in 25% aqueous HF. The enthalpies of formation were determined for calcined mesoporous silica (MS) and organic structure-directing agent (SDA) occluded samples (SDA: n-hexadeciltrimethylammonium bromide or CTAB, Pluronic P123, and Pluronic F127). The following are the measured interaction enthalpies between the MS and SDA: MCM-41/CTAB, −6.1 kJ/mol SiO₂; MCM-48/CTAB, −12.3 kJ/mol SiO₂; SBA-15/P123, −19.7 kJ/mol SiO₂; SBA-16/F127, −19.9 kJ/mol SiO₂. Per unit surface area, these interactions are −0.08, −0.15, −0.43, and −0.40 J/m², respectively. Though these SDA-framework interaction energies are still small in magnitude, they are somewhat more exothermic than those in silica zeolite formation, reflecting the greater metastability of the MS materials and the role of the long chain SDA in stabilizing and space-filling the large pores. The cubic MS (SBA) show stronger SDA interactions than the hexagonal (MCM). The interaction energies confirm a complex landscape of many competing structures of similar energy; with the role of SDA kinetic in selecting a specific structure rather than energetic in strongly stabilizing a given state, as has already been noted for zeolites. The enthalpies of the calcined MS relative to quartz determined by HF solution calorimetry in this study are in excellent agreement with those determined previously by high temperature oxide melt solution calorimetry.     

Deposition of Pd into mesoporous silica SBA-15 using supercritical carbon dioxide

Pd was deposited into mesoporous silica SBA-15 using supercritical CO₂ (scCO₂). Palladium hexafluoroacetylacetonate [Pd(hfac)₂] was dissolved in scCO₂ and impregnated into the support at very mild conditions, 40 °C and 85 bar. Then the organometallic precursor was reduced with H₂ in the CO₂ mixture or, after depressurization, in pure H₂. Materials were characterized by TGA, XRD, TEM, SEM, EDX, ICP-OES and N₂-adsorption experiments. Pd nanoparticles evenly distributed into the support (1-3 mol% Pd by ICP-OES) are only obtained when the reduction is performed in pure H₂. Cluster size is limited in two dimensions by the pore size of the support but clusters grow larger with increasing impregnation time and turn into small nanowires. The catalytic activity of the Pd/SiO₂ composite material was confirmed following the reduction of 4-nitrophenol to 4-aminophenol in water by UV-vis spectroscopy.     

A simple aqueous solution based chemical methodology for synthesis of Ag nanoparticles dispersed on mesoporous silicate matrix

A simple chemical method has been developed for preparation of Ag nanoparticles dispersed on mesoporous silicate matrix, SBA-15. Ag nanoparticles were uniformly dispersed on SBA-15 matrix by using the reduction reaction of AgNO₃ with trisodium citrate. The synthesized materials were characterized by using room temperature powder XRD analysis, N₂ adsorption-desorption isotherm, high resolution TEM and SEM. It was observed that the synthesized SBA-15 and Ag-SBA-15 have a surface area of 778 and 151 m²/g respectively. The synthesized materials have long range ordering of pores with narrow pore size distribution centered at ∼ 7 nm. Pore structure of SBA-15 remains preserved even after deposition of Ag nanoparticle. This chemical route reported here offers a simple method for preparation of Ag-SBA-15, where unagglomerated Ag nanoparticles (∼ 20 nm) are uniformly dispersed on SBA-15.     

Deactivation mechanism of Pd supported on ordered and non-ordered mesoporous silica in the direct H2O2 synthesis using CO2-expanded methanol

The deactivation mechanism of Pd supported on silica and mesoporous silica (SBA-15) using CO₂-expanded methanol as solvent was studied in the direct synthesis of H₂O₂ in batch and semi-continuous batch reactor tests as well as its hydrogenolysis. Fresh and used catalysts were characterized by TPR and CO chemisorption. The results evidence the presence of deactivation, which can be correlated to the loss of accessible active metal surface area due to sintering of Pd, but there is also an effect of the presence of the ordered mesoporous structure and of the reaction conditions. The higher concentration of H₂ in solution in semi-continuous batch reactor tests with respect to batch reactor tests leads to a more relevant deactivation in Pd-SiO₂ with respect to Pd-SBA-15, but a higher initial activity, due to the fact that H₂ accelerates the reduction of the Pd species which are less reducible in Pd-SiO₂ than in Pd-SBA-15. Pd-SBA-15 shows a higher H₂O₂ selectivity and productivity with respect to Pd-SiO₂ in batch reactor tests, related to the presence of easier reducible Pd species. Another difference is related to the different mechanism of sintering. On the SBA-15 support, due to the presence of the ordered mesoporosity, the Pd particles migrate into the SBA-15 channels forming elongated 1D-type particles. In Pd-SiO₂ catalyst, instead, the sintering of the Pd particles leads to large aggregates of Pd particles in the range of 20-25 nm.     

Low-temperature H2S removal from gas streams with SBA-15 supported ZnO nanoparticles

Mesoporous silica SBA-15 with zinc oxide (ZnO) nanoparticles was prepared via incipient wetness impregnation and ultrasonic method, followed by in situ activation at 523 K. The mesoporous materials obtained were characterized by ICP, XRD, FTIR, nitrogen adsorption, TEM and XPS. The prepared materials showed a superior ability to remove H₂S down to parts per billion (ppb) from gas stream at lower temperature (298 K), and the highest H₂S breakthrough capacity, 436 mg S/g adsorbent, was observed for SBA-15 with 3.04 wt% zinc loading. The enhancement of H₂S removal capacity was attributed to the integration of the high surface area of the mesoporous material and the promising desulphurization properties of ZnO nanoparticles. It was believed that ZnO-modified SBA-15 is a promising adsorbent for H₂S cleaning at ambient conditions, which will extend the application of the mesoporous materials to the environmental protection area.     

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）.     

Co3O4 and Mn3O4 Nanoparticles Dispersed on SBA-15: Efficient Catalysts for Methane Combustion

Co₃O₄ and Mn₃O₄ nanoparticles were successfully impregnated on SBA-15 mesoporous silica. A high dispersion of these metal oxide particles was achieved while using a “two-solvents” procedure, allowing a proper control of the metal oxides loading (7 wt%) and size (10–12 nm). These Co₃O₄ and Mn₃O₄ supported oxides on SBA-15 were characterised by means of XRD, BET and TEM techniques. The influence of the nature of the silica support was investigated in terms of porosity and specific surface area. Since, an improved catalytic activity was achieved over SBA-15 mesoporous silica; it appears that its organised porous meso-structure creates a confinement medium which permits a high dispersion of metal oxide nanoparticles. Supported Co₃O₄/SBA-15 (7 wt%) showed the highest catalytic performance in the combustion of methane under lower explosive limit conditions, comparable to perovskites. These materials become therefore novel efficient combustion catalysts at low metal loading.     

Improving the electrocapacitive properties of mesoporous CMK-5 carbon with carbon nanotubes and nitrogen doping

Nitrogen-containing carbon composite materials composed of mesoporous carbon CMK-5 and carbon nanotubes (CNTs) were prepared by the chemical vapor deposition method with Fe(NO₃)₃-impregnated SBA-15 as template and pyridine as the carbon precursor. The Fe nanoparticles confined in the channels of SBA-15 induced the formation of mesoporous carbon characteristic of CMK-5, whereas Fe particles homogeneously dispersed on the external surface of SBA-15 served as catalysts for CNTs growth. The contents of CNTs, the N doping level and the microstruture of the carbon composite were closely related to the initial Fe/Si atomic ratio in SBA-15 template. Incorporation of CNTs in the composite was found to substantially reduce the electric resistance, leading to the composite materials exhibiting excellent rate-performance. A maximum specific capacitance of 208 F/g and a power density of 10 kW/kg were achieved in 6.0 mol/L KOH aqueous electrolyte when these carbon composites were applied as supercapacitor electrodes. Moreover, the composite electrode also exhibited good electrochemical stability with no capacitance loss after 1000 cycles of galvanostatic charge-discharge process.     

Desulfurization of fuels by means of a nanoporous carbon adsorbent

Mesoporous carbon, CMK-3, was prepared using hexagonal Al-SBA-15 mesoporous silica, instead of SBA-15, as a template. The synthesized materials were examined via X-ray diffraction and N₂-adsorption. The mesoporous carbon was studied for its adsorption of dibenzothiophene (DBT) from petroleum fuels. The performance of this adsorbent was compared with SBA-15 and Al-SBA-15, through which CMK-3 showed higher sulfur adsorption capabilities due to a larger mesopore volume and a higher specific surface area. The uptake capacity for DBT followed the order CMK-3 > Al-SBA-15 > SBA-15. The results confirmed the importance of the adsorbent pore size and its surface chemistry for the adsorption of DBT from liquid phase.Langmuir and Freundlich isotherm models were used to fit equilibrium data for CMK-3. The equilibrium data were best represented by the Langmuir isotherm. Kinetic studies were carried out and showed the sorption kinetics of dibenzothiophene was best described by a pseudo-second-order kinetic model.     

Experimental investigation of thermo-physical properties of platelet mesoporous SBA-15 silica particles dispersed in ethylene glycol and water mixture

This paper presents an experimental investigation of thermophysical properties of platelet mesoporous SBA-15 particles dispersed in 60:40 (v/v) ethylene glycol:water mixture. The effect of weight fraction of particles and temperature is studied on density, viscosity and thermal conductivity of nanofluids. The maximum measured thermal conductivity enhancement reaches up to 22% for the nanofluids containing 5 wt% of SBA-15 at 60 °C. The SBA-15 nanofluids show Newtonian behavior in the tested temperature range. Also, the relative density increases between 0.4% and 2.2% when the weight percent of the nanoparticles varies between 1 and 5 at 60 °C. Structural and morphological characterization of synthesized SBA-15 have been carried out using Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and N₂ adsorption–desorption isotherms methods.     

Adsorption of l-histidine over mesoporous carbon molecular sieves

Mesoporous carbon, CMK-3, was prepared by large pore hexagonal mesoporous silica SBA-15. The structural order and textural properties of all the materials were studied by XRD, HRTEM, and nitrogen adsorption. Adsorption of l-histidine (His) over various porous adsorbents such as CMK-3, SBA-15, and activated carbon was studied from solutions with different pH. His adsorption was observed to be pH dependent with maximum adsorption near the isoelectric point of the amino acid. CMK-3 showed a larger amount of His adsorption as compared to SBA-15 and the conventional adsorbent, namely activated carbon. CMK-3 registers the total adsorption capacity of ca. 1350 μmol g⁻¹ which is ca. 12 times higher than the adsorption capacity of SBA-15. This large difference could be mainly due to the stronger hydrophobic interaction between the non-polar side chains of amino acids and the hydrophobic surface of the mesoporous carbon as compared to mesoporous silica. The influence of ionic strengths on the adsorption of His was also studied and the results are discussed. Nitrogen adsorption of CMK-3 after His adsorption confirmed that His molecules are tightly packed inside the mesopores.     

Pd/CMK-3的合成及其在Suzuki-Miyaura碳-碳偶联反应中的应用

利用介孔二氧化硅（SBA-15）为模板、蔗糖为碳源,制备了有序介孔碳材料CMK-3,然后以CMK-3为载体,利用浸渍还原法得到介孔碳负载Pd纳米粒子的复合催化剂（Pd/CMK-3）,通过XRD、TEM以及氮气吸附-脱附等手段对催化剂的微结构和组分进行分析,结果表明CMK-3为有序介孔结构,孔径约为5nm,Pd/CMK-3保留了介孔结构,且孔道中负载有不同尺寸的Pd粒子。应用于无配体催化的Suzuki-Miyaura相似文献   

Metal oxides nanoparticles on SBA-15: Efficient catalyst for methane combustion

Catalysts based on crystalline nanoparticles of Mn and Co metal oxides supported on mesoporous silica SBA-15 have been developed. These materials were characterized by XRD, BET and transmission electron microscopy (TEM) techniques. SBA-15 mesoporous silica was synthesized by a conventional sol–gel method using a tri-block copolymer as surfactant. Supported Mn₃O₄ and Co₃O₄ nanoparticles were obtained after calcination of as-impregnated SBA-15 by a metal salt precursor. The catalytic activity was evaluated in the combustion of methane at low concentration.Co₃O₄/SBA-15 (7 wt.%) exhibits the highest performance among the different oxides. Furthermore, this novel generation of catalysts appeared as active as conventional LaCoO₃ perovskite, usually taken as reference for this reaction. Thanks to its organized meso-structures, SBA-15 material creates peculiar diffusion conditions for reactants and/or products.