Titanosilsesquioxane Anchored on Mesoporous Silicas: A Novel Approach for the Preparation of Heterogeneous Catalysts for Selective Oxidations

CO2 free production of ethylene oxide via liquid phase epoxidation of ethylene using niobium oxide incorporated mesoporous silica material as the catalyst

Ethylene Oxide (EO) is an essential raw material used in various consumer products like different glycol derivatives, ethoxylates, and polymers. We hydrothermally synthesize niobium oxide incorporated with mesoporous silica material (Nb/MSM), an efficient catalyst for CO₂ free-ethylene oxide (EO) production via partial oxidation of ethylene. The structural properties of Nb/MSM catalysts were characterized using XRD, TEM, and N₂ adsorption-desorption. The catalytic activity of synthesized materials in liquid phase epoxidation (LPE) of ethylene was evaluated in the presence of peracetic acid (PAA) as an oxidant to avoid the production of CO₂ and also minimize metal leaching. GC chromatography was used to investigate the successful production of EO, and a peak with a retention time (RT) of 9.01 min served as confirmation. Various reaction parameters viz. temperature, catalyst concentration, ethylene to PAA molar ratio, and solvent effect were investigated in order to optimize the reaction conditions for enhancing the ethylene conversion and selectivity for EO production. By this approach, the challenges of greenhouse gas production and metal leaching were addressed which were associated with previously reported catalysts.

Zirconium and hafnium polyhedral oligosilsesquioxane complexes – green homogeneous catalysts in the formation of bio-derived ethers via a MPV/etherification reaction cascade

Newly designed POSS supported zirconium and hafnium isopropoxides are robust, durable and selective homogeneous catalysts for the conversion of hydroxymethylfurfural to bis(isopropoxymethyl)furane via MPV/etherification reaction with isopropanol as a green solvent/reagent.

POSS nanostructures in catalysis

In this review we highlight the use of appealing POSS-based nanostructures for both homogeneous and heterogeneous catalytic applications.

Ethoxy and silsesquioxane derivatives of antimony as dopant precursors: unravelling the structure and thermal stability of surface species on SiO2

We report here the controlled preparation of SiO₂ supported Sb-(mono)layers and their thorough characterization (in situ IR, solid-state NMR, elemental analyses) for the non-destructive Sb-doping of semiconductors.

Epoxy Resin Composite Based on Functional Hybrid Fillers

A study was carried out involving the filling of epoxy resin (EP) with bentonites and silica modified with polyhedral oligomeric silsesquioxane (POSS). The method of homogenization and the type of filler affect the functional and canceling properties of the composites was determined. The filler content ranged from 1.5% to 4.5% by mass. The basic mechanical properties of the hybrid composites were found to improve, and, in particular, there was an increase in tensile strength by 44%, and in Charpy impact strength by 93%. The developed hybrid composites had characteristics typical of polymer nanocomposites modified by clays, with a fine plate morphology of brittle fractures observed by SEM, absence of a plate separation peak in Wide Angles X-ray Scattering (WAXS) curves, and an exfoliated structure observed by TEM.

Rational design of single-site heterogeneous catalysts: towards high chemo-, regio- and stereoselectivity

The main methods for the design and preparation of single-site heterogeneous catalysts on inorganic oxide supports are described and reviewed. Catalytically active metal sites can be either introduced into the framework of porous materials via direct synthesis or added to a pre-existing support by post-synthesis techniques. Particular attention is paid to selected examples where the geometry, the nature and the chemical surroundings of the active single site is a key factor to obtain catalytic systems with enhanced chemo-, regio- and stereoselectivity. The ever-increasing capabilities of ‘nanoarchitecture’ at molecular level enable chemists to build ideal catalysts for the sustainable transformation of bulky and high added-value molecules.

Design and use of nanostructured single-site heterogeneous catalysts for the selective transformation of fine chemicals

Nanostructured single-site heterogeneous catalysts possess the advantages of classical solid catalysts, in terms of easy recovery and recycling, together with a defined tailored chemical and steric environment around the catalytically active metal site. The use of inorganic oxide supports with selected shape and porosity at a nanometric level may have a relevant impact on the regio- and stereochemistry of the catalytic reaction. Analogously, by choosing the optimal preparation techniques to obtain spatially isolated and well-characterised active sites, it is possible to achieve performances that are comparable to (or, in the most favourable cases, better than) those obtained with homogeneous systems. Such catalysts are therefore particularly suitable for the transformation of highly-functionalised fine chemicals and some relevant examples where high chemo-, regio- and stereoselectivity are crucial will be described.

Tripodal tetrahedral titanium coordination in the silica-grafted titania epoxidation catalysts: is not it only a myth? Selective formation of [Cy7Si7O12Ti]2(mu-OR)2(mu-ROH) cores on thermal "dissociation" of alkoxytitanasilsesquioxanes

The molecular structures of the species crystallizing from solutions of alkoxytitanasilsesquioxanes in hydrocarbons upon reflux confirm the partial release of solvating alcohol. They feature, however, distinctly the formation of a dinuclear core with preserved hexacoordination for the metal atoms. The active titanium centers in the silica-titania epoxidation catalysts, lacking the sterically demanding ligands, are thus quite probably also hexacoordinated.