A New Templated Ordered Structure with Combined Micro- and Mesopores and Internal Silica Nanocapsules (original) (raw)

A Brief Overview of Recent Progress in Porous Silica as Catalyst Supports

Journal of Composites Science

Porous silica particles have shown applications in various technological fields including their use as catalyst supports in heterogeneous catalysis. The mesoporous silica particles have ordered porosity, high surface area, and good chemical stability. These interesting structural or textural properties make porous silica an attractive material for use as catalyst supports in various heterogeneous catalysis reactions. The colloidal nature of the porous silica particles is highly useful in catalytic applications as it guarantees better mass transfer properties and uniform distribution of the various metal or metal oxide nanocatalysts in solution. The catalysts show high activity, low degree of metal leaching, and ease in recycling when supported or immobilized on porous silica-based materials. In this overview, we have pointed out the importance of porous silica as catalyst supports. A variety of chemical reactions catalyzed by different catalysts loaded or embedded in porous silica s...

Functionalized Ordered Mesoporous Silicas (MCM-41): Synthesis and Applications in Catalysis

Catalysts

Mesoporous silica sieves are among the most studied nano-objects due to their stable pore structure and easy preparation. In particular, MCM-41 have attracted increasing research attention due to their chemical versatility. This review focuses on the synthesis and regioselective functionalization of MCM-41 to prepare catalytic systems. The topics covered are: mono and di-functionalized MCM-41 as basic and acid catalysts, catalysts based on metallic complexes and heteropolyacids supported onto MCM-41, metallic nanoparticles embed onto functionalized MCM-41 and magnetic MCM-41 for catalytic purposes.

Functional silica monoliths with hierarchical uniform porosity as continuous flow catalytic reactors

Microporous and Mesoporous Materials, 2011

Silica rod monoliths of 6 mm diameter and 1-5 cm length were obtained by phase separation between silica gel and water in presence of aqueous soluble polyethylene oxide (spinodal decomposition). They exhibit a three-dimensional network of uniform flow-through macropores with adjustable size between 5 and 25 lm. The skeleton of the monolith has a thickness comparable to the size of the macropores and is composed of amorphous silica with a mesoporosity adjustable between 7 and 35 nm. These monolith rods, called MonoSil, were cladded and used as continuous flow catalytic microreactors after introduction of the active sites, via grafting of organic functions, as sulfonic acid groups (HSO 3-MonoSil) and inorganic species, as aluminium oxide (Al-MonoSil); or via the transformation of the amorphous silica skeleton into MCM-41, ZSM-5 and zeolite A (LTA-MonoSil) by a pseudomorphic transformation process with the preservation of the macroporous network. LTA-MonoSil was used in catalysis after cationic exchange of the former Na + cations with K + cations to yield to K-LTA-MonoSil exhibiting strong basic sites. The catalytic behavior of these modified monoliths was evaluated as continuous flow microreactors for the triacetine transesterification, the Diels-Alder reaction and the Knoevenagel condensation. These monolithic reactors demonstrated higher productivities than batch or packed-bed reactors for the described reactions.

Additive-free synthesis of robust monolithic mesoporous silica support used in catalysis

Ceramics International, 2018

Use of mesoporous silica as functional material or as support in adsorption and catalysis has been very limited in commercial terms due to limitations of powder morphology and accompanied handling and recycling issues. Previous reports on preparations of monolithic mesoporous silica generally indicate complicated procedures and/or deterioration of final structure. In this research, a simple scalable one-pot sol-gel synthesis with subsequent free atmospheric evaporation is applied to prepare monolithic mesoporous silica (of MSU family). Effects of synthesis parameters such as reagent concentrations and additives on both nano-structure and physical stability of the monolith were investigated. No-additive synthesis resulted in the most robust monolith under mechanical handling and hydrodynamic conditions. Material's disintegration rate in agitated water was as low as 0.1 mg/h and its structural stability was approved under hydrothermal conditions. The monolithic mesoporous silica samples functionalized with acid and base surface groups were used independently in catalytic esterification and transesterification reactions. At relatively low temperatures (~50°C), conversion of stearic acid to ethyl stearate was completed in the presence of monolithic acid catalyst. At the same conditions, above 50% and 20% conversions of triacetin to ethyl acetate (as a typical biodiesel production method) were achieved in the presence of monolithic acid and base catalysts respectively.

Synthesis of new silicas with high stable and large mesopores and macropores for biocatalysis applications

Materials Science and Engineering: C, 2012

Large mesoporous silica role of CTAB and EtAc Hydrolytic stability Monomodal or bimodal porous silicas with large mesopores, constituted by particles or having a monolithic (block type) morphology, respectively, are synthesized using sodium silicate as siliceous species source, cetyltrimethylammonium bromide (CTAB) as pore template and ethyl acetate (EtAc) as pH modifier. The monomodal porosity is represented by 20-30 nm pores and the bimodal one by these pores and also macropores. These characteristics are modulated in function of the CTAB and EtAc concentrations as well as the pH and hydrothermal treatment. The role of these reagents upon the porosity is rationalized. The presence of high CTAB concentration and a rather low pH decreasing rate (function of EtAc concentration and hydrothermal treatment) are essential for having the already known bimodal mesoporous silicas (BMS). On the contrary a rather high pH decreasing rate promotes the formation of the new bimodal mesoporous-macroporous silicas (BMMS) synthesized in this work, where the EtAc also plays the role of emulsion forming agent. The hydrolytic stability of the synthesized silica under aqueous conditions, at different pH values, makes these silicas good candidates for application in different areas of catalysis, especially in the enzymatic one.

Microporous and Mesoporous Molecular Sieves as Multifunctional Catalysts

ChemInform, 2007

A general trend in academic and industrial research is the transformation of homogeneously catalysed reactions into heterogeneous processes, using solids as supports of the active sites, in order to develop greener and economically competitive processes for the synthesis of chemicals.