Mesoporous organic-inorganic hybrid materials, a new class of materials characterized by large specific surface areas and pore sizes between 2 and 15 nm, have been obtained through the coupling of inorganic and organic components by template synthesis. The incorporation of functionalities can be achieved in three ways: by subsequent attachment of organic components onto a pure silica matrix (grafting), by simultaneous reaction of condensable inorganic silica species and silylated organic compounds (co-condensation, one-pot synthesis), and by the use of bissilylated organic precursors that lead to periodic mesoporous organosilicas (PMOs). This Review gives an overview of the preparation, properties, and potential applications of these materials in the areas of catalysis, sorption, chromatography, and the construction of systems for controlled release of active compounds, as well as molecular switches, with the main focus being on PMOs.

Silica-based mesoporous organic-inorganic hybrid materials.

3. Soluble Metal Oxides 2459 3.1. Polyoxometalates 2459 3.2. Peroxotungstates 2459 3.3. Peroxomolybdates 2460 3.4. Methyltrioxorhenium 2461 3.5. Other Metal Oxides 2461 4. Metal Oxides Generated in Situ 2461 4.1. Selenium and Arsenic Compounds 2461 4.2. Simple Metal Salts 2462 5. Coordination Complexes 2463 5.1. Manganese Porphyrins 2463 5.2. Iron Porphyrins 2464 5.3. Manganese Salen Complexes 2466 5.4. 1,4,7-Triazacyclononane (TACN) Complexes 2466 5.5. Iron and Manganese Pyridyl-Amine Complexes 2468

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Metal-Catalyzed Epoxidations of Alkenes with Hydrogen Peroxide

Alternatives to petroleum-derived fuels and chemicals are being sought in an effort to improve air quality and increase energy security through development of novel technologies for the production of synthetic fuels and chemicals using renewable energy sources such as biomass. In this context, ethanol is being considered as a potential alternative synthetic fuel to be used in automobiles or as a potential source of hydrogen for fuel cells as it can be produced from biomass. Renewable ethanol can also serve as a feedstock for the synthesis of a variety of industrial chemicals and polymers. Currently, ethanol is produced primarily by fermentation of biomass-derived sugars, especially those containing six carbons, whereas 5-carbon sugars and lignin, which are also present in the biomass, remain unusable. Gasification of biomass to syngas (CO + H2), followed by catalytic conversion of syngas, could produce ethanol in large quantities. However, the catalytic conversion of syngas to ethanol remains challenging,...

A Review of Recent Literature to Search for an Efficient Catalytic Process for the Conversion of Syngas to Ethanol

Perovskites as substitutes of noble metals for heterogeneous catalysis: dream or reality.

Many efforts have been made to develop new catalysts to oxidize cyclohexane under mild conditions. Herein, we review the most interesting systems for this process with different oxidants such as hydrogen peroxide, tert -butyl hydroperoxide and molecular oxygen. Using H 2 O 2 , Na-GeX has been shown to be a most stable and active catalyst. Mesoporous TS-1 and Ti-MCM-41 are also stable, but the use of other metals such as Cr, V, Fe and Mo leads to leaching of the metal. Homogeneous systems based on binuclear manganese(IV) complexes have also been shown to be interesting. When t -BuOOH is used, the active systems are those phthalocyanines based on Ru, Co and Cu and polyoxometalates of dinuclear ruthenium and palladium. Microporous metallosilicates containing different transition metals showed leaching of the metal during the reactions. Molecular oxygen can be used directly as an oxidant and decreases the leaching of active species in comparison to hydrogen peroxide and tert -butyl hydroperoxide. Metal aluminophosphates (metal: Mn, Fe, Co, Cu, Cr V) are active and relatively stable under such conditions. Mn-AlPO-36 yields directly adipic acid, but large amounts of carboxylic acids should be avoided, as they cause metal leaching from the catalysts. Rare earth exchanged zeolite Y also shows good selectivity and activity. In the last part of the review, novel alternative strategies for the production of cyclohexanol and cyclohexanone and the direct synthesis of adipic acid are discussed.

Cyclohexane oxidation continues to be a challenge

Effect of alkali additives over nanocrystalline Co–Cu-based perovskites as catalysts for higher-alcohol synthesis

Two LaCo 0.7 Cu 0.3 O 3 perovskite catalysts synthesized by reactive grinding and by the citrate complex method have been characterized by X-ray diffraction (XRD), BET, SEM, H 2 -temperature-programmed reduction (TPR) and tested for the synthesis of higher alcohols and hydrocarbons from syngas. The ground sample shows a rather high surface area and nanometric particles. The coexistence of copper and cobalt in the perovskite lattice provides a highly dispersed bimetallic phase after pretreatment under hydrogen. Both samples were reduced in situ prior to being tested for the synthesis of alcohols and hydrocarbons. The catalytic activity and product distribution depend strongly on the process variables, alkali promoter, preparation method, and catalyst morphology. While the ground perovskite is rather selective for the synthesis of higher alcohols, the citrate-derived precursor produces mainly methane and light hydrocarbons in addition to 10–15 wt.% of alcohols. The optimum parameters for catalyst preparation and for alcohol synthesis were determined. Under the optimal reaction conditions, the alcohol productivity is in a broad range of 70–140 mg/g cat /h and the selectivity towards alcohols is about 40–45 wt.%. Both alcohols and hydrocarbons produced obey a classical Anderson–Schulz–Flory (ASF) plot carbon number distribution. The nanocrystalline perovskite precursor shows a better catalytic performance compared to the citrate-derived sample in terms of both alcohol selectivity and productivity. The catalytic stability of the ground perovskite is dependent not only on the crystal domain size (or the size of nanoparticles) and the amount of remnant sodium ions, but also strongly on the compactness of nanoparticles. The existence of slit-shaped spaces between primary nanoparticles and/or grain boundaries hinders the formation of long carbon chains, which are precursors for the formation of coke on the catalyst surface.

M. Hassan Zahedi-Niaki

Papers

Effect of alkali additives over nanocrystalline Co–Cu-based perovskites as catalysts for higher-alcohol synthesis

Conversion of syngas to higher alcohols over nanosized LaCo0.7Cu0.3O3 perovskite precursors

1-Butanol etherification over sulfonated mesostructured silica and organo-silica

H2O2 oxidation and epoxidation of hydrocarbons and alcohols over titanium aluminophosphates TAPO-5, TAPO-11, and TAPO-36

Acid properties of titanium aluminophosphate molecular sieves