Selective Oxidation in Supercritical Carbon Dioxide Using Clean Oxidants

Abstract

We have systematically investigated heterogeneous catalytic oxidation of different substrates in supercritical carbon dioxide (SC-CO 2 ). Three types of catalysts, a metal complex {cis-[Fe-(dmp) 2 (H 2 O) 2 ] (CF 3 SO 3 ) 2 } (dmp ) 2,9-dimethyl-1,10-phenanthroline), 0.5% platinum γ-alumina, and 0.5% palladium γ-alumina, were used at a pressure of 200 bar, at temperatures from 60 to 150°C, and for 3-18 h for partial oxidation of organic substrates. The metal-oxo catalyst used gave as high as 3.9% conversion of cycloxene to its oxides and epoxides, with the major products being the ketone and alcohol. The oxidation of cyclohexene strongly depended on the concentration of oxygen, whereas length of reaction (3-18 h) and temperature (60-150°C) were shown to be less significant on the conversion and selectivity of the reaction. Oxidation of cyclohexene over Pd and Pt/Al 2 O 3 catalysts resulted in a mixture of dehydrogenation and oxygenated products.

Catalytic Performance of Fe(II)-Scorpionate Complexes towards Cyclohexane Oxidation in Organic, Ionic Liquid and/or Supercritical CO2 Media: A Comparative Study

“…Temperature and pressure have been shown to affect the reaction rate and conversion of cyclohexane [6], providing tunability of reactions in SCFs. Despite these encouraging results, homogeneous catalytic oxidations remain relatively unexplored in scCO 2 [9][10][11].…”

Highly Efficient Oxidation of Toluene to Benzoic Acid Catalyzed by Manganese Dioxide and N-Hydroxyphthalimide

“…The vapor-phase oxidations of toluene [10][11][12], especially catalyzed by V-oxides supported on TiO 2, had been investigated, showing the advantage of separation and so on, but the highly specialized equipment and high temperature were required. The attempts using heterogeneous catalyst [3,4,[13][14][15][16][17] and supercritical fluids as reaction mediators [5,[18][19][20] had also been made to make this oxidation more environmentally benign. However, the low catalytic activities and expensive solvents limited the application of these methods.…”

A New Oxidation Catalyst System using Fluorous Cobalt(II) Species in Water-supercritical Carbon dioxide (C–H free environment)

“…In addition, the low energy efficiency, use of corrosive and toxic acetic acid, product over-oxidation, difficulty in solvent and catalyst recovery, and explosion hazards associated with the solvent and dioxygen (with reported explosions) are also obvious [4]. With increasingly demanding environmental legislation, public and corporate pressure, and the disadvantages of this technology, the process is becoming less economically competitive [5].…”