Due to the uniform and stable pore structure, mesoporous silica has attracted increasing research attention as a catalyst support material As a large family of mesoporous silica-supported materials, noble-metal nanoparticles supported on mesoporous silica catalysts have demonstrated desirable properties across a broad platform of reactions In this review article, we first introduce systems of metal nanoparticles dispersed on mesoporous silica, and then, we focus on next generation systems, in which the noble metal is not supported on the mesoporous silica but rather entrapped/intercalated within the silica matrix, thus enhancing particle stability and in some cases, enhanced activity Herein, research and future directions on both synthesizing hybrid noble-metal nanoparticles/mesoporous silica composite catalysts and their resultant properties will be discussed

Hybrid Mesoporous Silica/Noble-Metal Nanoparticle Materials—Synthesis and Catalytic Applications

Cobalt substituted mesoporous SBA-16 catalysts, made by post grafting technique using directly cobalt acetylacetonate as the precursor was prepared. High loading of cobalt finely dispersed on SBA-16 silica was obtained. The Co/SBA-16 catalysts exhibited high conversion and selectivity in epoxidation of limonene towards limonene epoxides with molecular oxygen as the most desirable oxidant and isobutyraldehyde as co-reagent under very mild conditions in the presence of the green solvent ethylacetate. A variety of characterization techniques such as nitrogen physisorption, XRD, DR-UV–vis, XPS, TEM indicates that the proposed impregnation procedure is a highly tunable and reproducible strategy to disperse transition metals in mesoporous silica materials. The unique pore structure of Co/SBA-16 catalysts could be beneficial for the epoxidation of bulky alkene molecules. The reaction conditions were systematically investigated using a statistical experimental design. Repeated catalytic tests showed no remarkable difference in the activity of fresh and recycled catalysts over three process cycles.

Aerobic epoxidation of limonene using cobalt substituted mesoporous SBA-16 Part 1: Optimization via Response Surface Methodology (RSM)

Fe-MCM-41 and Fe-SBA-15, two different iron-containing mesoporous silicas, were successfully synthesized by a straightforward and versatile method using iron acetylacetonate as a metal precursor. pH adjustment with ammonia during the synthesis was found to be an efficient way to improve the iron content. Physicochemical parameters of the iron-containing mesoporous silicas were obtained by nitrogen physisorption measurements, and the coordination environment of iron elements was validated by UV–vis diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy. The surface acidity was tested by using a series of Hammett indicators. To further distinguish the Lewis acid sites on the surface, a pyridine adsorption FT-IR method was implemented. These prepared nanoporous catalysts were screened in the Mukaiyama aldol reaction as a model reaction catalyzed by a Lewis acid. The Lewis acid catalytic activity of the materials was fine-tuned, and the corresponding aldol products were obtained in good yield a...

/pdf/iron-modified-mesoporous-silica-as-an-efficient-solid-lewis-49b0m3zr4n.pdf

Iron-Modified Mesoporous Silica as an Efficient Solid Lewis Acid Catalyst for the Mukaiyama Aldol Reaction

Preparation of nickel (oxide) nanoparticles confined in the secondary pore network of mesoporous scaffolds using melt infiltration

Cu-doped rod-shaped mesoporous silica nanoparticles (Cu-RMSN) were synthesized by a new one-step approach based on in situ functionalization procedure referring to the phenomenon of micellar solubilization. SEM and TEM studies revealed the rod-like morphology of uniformly sized particles with longitudinal mesopore channels. The BET specific surface areas were near 500 m2 g–1 and the average pore diameter varied from 3 to 3.6 nm. The composite Cu-RMSN proved to be an efficient heterogeneous catalyst for a microwave-assisted three-component 1,3-dipolar cycloaddition reaction in aqueous solution. The one-pot preparation of 1,4-dibustituted-1,2,3-triazole derivatives was straightforward and high yielding, due to the high copper dispersion at the pore surface resulting in the high accessibility of the active sites. The efficiency of the catalyst was also demonstrated upon recycling, making such synthesis a truly green process with marked step and solvent economy and important waste reduction.

https://hal.archives-ouvertes.fr/hal-02875562/document

Copper-Containing Rod-Shaped Nanosized Silica Particles for Microwave-Assisted Synthesis of Triazoles in Aqueous Solution

A series of transition metal acetylacetonates and acetates were used as precursors to generate high loadings of metal sites finely dispersed on SBA-15 silica. To achieve this, grafting of chelated transition metal precursors was performed directly to the surface of the as-synthesized SBA-15/P123 composite material. The thus-obtained metal/SBA-15 materials were studied by a variety of methods, e.g., elemental analysis, Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance UV–visible spectroscopy (DR-UV–vis), X-ray photoelectron spectroscopy (XPS) and N 2 physisorption measurements at −196 °C. From the results, the proposed functionalization method was found to be a highly tunable and reproducible strategy to disperse transition metal oxides in mesoporous silica materials. The results from elemental analysis of the modified materials confirmed that the amount of grafted species is a function of the initial concentration of precursor in the solution used for grafting. The chelated complexes were found to strongly interact with the silanol groups of the silica material, resulting in a ligand-exchange process, as corroborated by FTIR. However, different metal precursors showed distinct reactivity towards the surface of mesoporous silica, owing to differences in the stability of the complexes under the conditions used for grafting. DR-UV–vis and XPS analyses suggest that when the stability of a given precursor decreases, the grafting procedure can lead to the formation of small clusters of the metal oxide on the silica surface. XRD and SEM also show that grafting of lower stability complexes, such as Mn(acac) 3 , Cu(acetate) 2 and VO(acac) 2 , on the silica surface can result in the formation of large crystals on the external surface of the SBA-15 particles. Nevertheless, it was established by XPS analysis that only a small percentage of the grafted species leads to the formation of bulk crystals while the remaining species are substituted into the silica framework. Obviously, a well-controlled and increased dispersion of the metal cations/oxides on the surface of highly porous silica materials is of great interest since these M x O y –SiO 2 mixed oxides could demonstrate high catalytic activity in a large variety of reactions.

A generalized method toward high dispersion of transition metals in large pore mesoporous metal oxide/silica hybrids.

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A generalized method toward high dispersion of transition metals in large pore mesoporous metal oxide/silica hybrids.