Oxygen reduction, trapping

Wang JX, Zhang JL, Adzic RR. 2007. Double-trap kinetic equation for the oxygen reduction reaction on Pt(lll) in acidic media. J Phys Chem A 111 12702-12710. 

As in the reductive ring-opening, titanocene—oxygen bonds have to be protonated. Here, a titanium enolate, which is generated after reductive trapping of an enol radical, has to be protonated, in addition to a simple titanocene alkoxide. As before, 2,4,6-collidine hydrochloride constitutes a suitable acid to achieve catalytic turnover, but here zinc dust turned out to be the reductant of choice [31c], The features of the stoichiometric reaction are preserved under our conditions. Acrylates and acrylonitriles are excellent radical acceptors in these reactions. Methyl vinyl ketone did not yield the desired addition product. Under the standard reaction conditions, a-substituted acceptors are readily tolerated, but (3-substitution gives the products only in low yields. 

Photocatalytic reductions are not observed as frequently as photocatalytic oxidations. This is due to the fact that the reducing power of a conduction band electron is significantly lower than the oxidizing power of a valence-band hole and because most reducible substrates do not compete kinetically with oxygen in trapping photogenerated conduction band electrons. Most photocatalytic reductions require a co-catalyst such as platinum. 

A trap packed with stainless steel helices and cooled in dry ice-acetone produced no significant reduction in the amount of oxidant formed upon irradiation of air passed through the trap. When a liquid oxygen-cooled trap was used in series with the dry ice trap, essentially complete retention of the oxidant precursors resulted (Figure 17). Upon removal of the coolant bath, the bulk of the precursors was released (Figure 17). Thus, this technique for the collection and concentration of the substances which yield oxidant on irradiation promised to make their analysis feasible and gave hope for their eventual identification. 

The Barton decarboxylation procedure was used in the total synthesis of (-)-verrucarol by K. Tadano et al. The initially formed thiohydroxamic ester was decarboxylated to leave a methylene radical on the cyclopentyl ring, which was then trapped by molecular oxygen. Reductive work-up in the presence of f-BuSH finally provided the hydroxylated product. ... 

Tin corrodes in oxygenated solutions. Some oxygen is trapped within the tin can. However, as soon as the amount of oxygen is consumed by cathodic reduction, the dissolution of tin stops. 

Okada, T, Satou, H. and Yuasa, M. (2003) Effects of additives on oxygen reduction kinetics at the interface between platinum and perfluorinated ionomer. Langmuir 19, 2325-2332 Panchenko, A., Dilger, H., Kerres, J., Hein, M., Ullrich, A., Kaz, T. andRoduner, E. (2004) In-situ spin trap electron paramagnetic resonance study of fuel cell processes. Phys. Chem. Chem. 

No clear picture of the primary radical intermediate(s) in the HO2 photooxidation of water has appeared. The nature of the observed radical species depends on the origin and pretreatment of the HO2 sample, on the conditions and extent of its reduction, on the extent of surface hydroxylation, and on the presence of adventitious electron acceptors such as molecular oxygen (41). The hole is trapped on the terminal OH group (54). 

The next phase of the synthesis was construction of the C-ring. An aldol addition was used to introduce a 3-butenyl group at C(8) and the product was trapped as a carbonate ester. The Davis oxaziridine was then used to introduce an oxygen at C(2). After reduction of the C(3) oxygen, a cyclic carbonate was formed, and C(2) was converted... 

The impact of oxygen storage in DeNO catalysis in 02 excess is more complex and strongly depends on the process used for NO reduction. The impact of OSC materials will be examined on two processes the selective reduction by HC (HC-SCR) and the NO -trap process. 

Another important catalytic technology for removal of NOx from lean-burn engine exhausts involves NOx storage reduction catalysis, or the lean-NOx trap . In the lean-NOx trap, the formation of N02 by NO oxidation is followed by the formation of a nitrate when the N02 is adsorbed onto the catalyst surface. Thus, the N02 is stored on the catalyst surface in the nitrate form and subsequently decomposed to N2. Lean NOx trap catalysts have shown serious deactivation in the presence of SOx because, under oxygen-rich conditions, SO, adsorbs more strongly on N02 adsorption sites than N02, and the adsorbed SOx does not desorb altogether even under fuel-rich conditions. The presence of S03 leads to the formation of sulfuric acid and sulfates that increase the particulates in the exhaust and poison the active sites on the catalyst. Furthermore, catalytic oxidation of NO to N02 can be operated in a limited temperature range. Oxidation of NO to N02 by a conventional Pt-based catalyst has a maximum at about 250°C and loses its efficiency below about 100°C and above about 400°C. 

---