Dalmo Mandelli

Cyclohexane oxidation continues to be a challenge

Abstract 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.

Alumina-catalyzed alkene epoxidation with hydrogen peroxide

Abstract Inexpensive Al 2 O 3 can be used as a simple catalyst for alkene epoxidation, using anhydrous hydrogen peroxide as oxidant. This system is active and selective in the epoxidation of several alkenes. Besides the epoxidation of the terpenes limonene and α-pinene, we studied the epoxidation of cyclohexene and cyclooctene, as well as α-olefins, such as 1-octene and 1-decene. Productivities of up to 4.3xa0g products per gram catalyst were obtained and the catalyst was recycled without significant loss of activity.

Activity, selectivity and stability of metallosilicates containing molybdenum for the epoxidation of alkenes

Abstract Microporous metallosilicates containing various transition metals have been prepared by the acid-catalyzed sol–gel process. The catalytic activity of the materials has been tested for the epoxidation of cyclooctene with tert -butyl hydroperoxide. Silicates containing molybdenum showed high activities and epoxide selectivities. The catalytic activities of catalysts prepared with molybdenyl acetylacetonate as metal precursor are mainly due to metal leached into the homogeneous phase. A catalyst for the heterogeneous phase epoxidation was obtained, using Mo(V)isopropoxide as metal precursor. This catalyst was tested in the epoxidation of various alkenes and conversions increase in the order 1-decene≈α-pinene 2 -physisorption, UV–VIS and FTIR spectroscopy.

Epoxidation of alkenes with hydrogen peroxide catalyzed by ReO4-SiO2.Al2O3 and ReO4-Al2O3

Abstract Rhenium oxides supported on zeolite Y, mixed silica–alumina and pure alumina were prepared by impregnation of the supports with Re 2 O 7 or NH 4 ReO 4 . The materials are active catalysts in the epoxidation of cyclooctene and cyclohexene with anhydrous H 2 O 2 in EtOAc. Catalyst stabilities with regard to metal leaching are closely correlated with the alumina content of the support and almost no leaching was observed with ReO 4 − supported on pure alumina. Stable catalysts ReO 4 –Al 2 O 3 with ReO 4 − contents up to 12xa0wt.% can be prepared. Higher contents result in extensive metal leaching and catalysis in the homogeneous phase. The catalyst ReO 4 (12xa0wt.%)–Al 2 O 3 was re-used in three catalytic runs, without loss of activity. Selectivities for cyclooctene epoxide were around 96%, whereas cyclohexanediol was obtained as the only product in cyclohexene epoxidation. Adding pyridine to the reaction mixtures, the selectivity for cyclohexene epoxide increased from 0 to 67%, however, a significant decrease in conversion was observed.

27-P-06-Microporous metallosilicates for the oxidation of hydrocarbons: preparation, characterization and catalytic activity

Publisher Summary This chapter discusses the preparation, characterization, and catalytic activity of microporous metallosilicates for the oxidation of hydrocarbons. Metallosilicates containing chromium (Cr), copper (Cu), or molybdenum (Mo) are prepared by an acid-catalyzed sol-gel process. Structural information about the silicates are obtained by elemental analysis, thermogravimetric analysis (TGA), X-ray diffraction (XRD), N2-physisorption, electron paramagnetic resonance (EPR), ultraviolet/visible (UV/VIS), and Fourier transform infrared spectroscopy (FTIR) spectroscopy. The silicates are active catalysts for the oxidation of hydrocarbons with tert-butyl hydroperoxide. Catalyst stabilities with respect to metal leaching during catalytic oxidations are investigated.