Catalysts, hydrogen peroxide formation

Then, the catalytic action is performed under homogeneous conditions and, at the end of the reaction, H2O2 being completely consumed, the precatalyst precipitates and can be easily filtered off and recovered. Both conversions and selectivities of this method are very good. Finally, as in the case of TS-1, this epoxidation system was combined with the 2-ethylanthra-quinone (EAQ)/2-ethylanthrahydroquinone (EAHQ) process for hydrogen peroxide formation, and good conversion and selectivity were obtained for propylene oxide in three consecutive cycles. The catalyst was recovered and reused in between every cycle (Scheme 5) ... 

In several cases, the in situ formation of hydrogen peroxide is the first step of the process. Thus, phenol can be obtained from benzene, carbon monoxide (5 atm) and oxygen (65 atm) at 70 °C in a benzene-water-methyl isobutyl ketone mixture, with TS-1 and a palladium complex as catalysts [26]. Despite a 91% selectivity to phenol, benzene conversion (3.2%) and productivity are still too low for industrial application. The palladium complex is required to promote hydrogen peroxide formation upon reaction of oxygen, carbon monoxide and water [27[. 

H. Munakata, Y. Oumi, A. Miyamoto, A DET study on peroxo-complex in titanosilicate catalyst Hydrogen peroxide activation on titanosilicalite-1 catalyst and reaction mechanisms for catalytic olefin epoxidation and for hydroxylamine formation from ammonia, J. Phys. Chem. B 105 (2001) 3493. 

V vs. SHE in 0.1 mol dm H2SO4 at room temperature [74], The effect of the addition of zirconium was also investigated to enhance the ORR activity [76], The Ba-Nb-Zr-O-N/CB showed higher ORR activity with the ORR onset potential of ca. 0.93 V. The ORR proceeded primarily via a four-electron transfer reaction to water, and the maximum proportion of the hydrogen peroxide formation was less than 12 %. The incorporatiOTi of Ba and Nb into Zr" " matrix may have affected the surface structure and/or state of the catalyst, possibly causing the high ORR activity. 

Much research was and is focused on ODCs for chlor-alkali electrolysis which are based on carbon carrier materials [4]. However, until now the stability of such ODCs is insufficient. The most probable reason is the formation of hydrogen peroxide species which attack the carbon and destroy the connection between catalyst metal and carbon carrier. Using pure silver as catalyst, no peroxide formation has to be expected. 

Depending on the amount and the distribution of selenium, up to 5% hydrogen peroxide formation has been observed in the oxygen reduction reaction. As hydrogen peroxide leads to a rapid degradation of the membrane and the gas diffusion media and enhances the corrosion of the carbon catalyst support and finally to a loss of performance due to this side reaction, the formation of hydrogen peroxide has to be minimized. Further details on the effect of particle size, particle distribution and the effect of the carbon support on the hydrogen peroxide production has been mentioned above. 

Inaba, M., Yamada, H., Tokunaga, J., and Tasaka, A. 2004. Effect of agglomeration of Pt/C catalyst on hydrogen peroxide formation. Electrochemical and Solid-State Letters 7 A474-A476. 

As the potential of this technology is tremendous, companies are putting their effort in investigating the reaction kinetics and stability of hydrogen peroxide formation in a microreactor. Some such studies are performed at BASF Catalyst [57] and give a promising input for optimizing the reaction for more efficient... 

Derivative Formation. Hydrogen peroxide is an important reagent in the manufacture of organic peroxides, including tert-huty hydroperoxide, benzoyl peroxide, peroxyacetic acid, esters such as tert-huty peroxyacetate, and ketone derivatives such as methyl ethyl ketone peroxide. These are used as polymerization catalysts, cross-linking agents, and oxidants (see Peroxides and peroxide compounds). 

Oxidation. Maleic and fumaric acids are oxidized in aqueous solution by ozone [10028-15-6] (qv) (85). Products of the reaction include glyoxyhc acid [298-12-4], oxalic acid [144-62-7], and formic acid [64-18-6], Catalytic oxidation of aqueous maleic acid occurs with hydrogen peroxide [7722-84-1] in the presence of sodium tungstate(VI) [13472-45-2] (86) and sodium molybdate(VI) [7631-95-0] (87). Both catalyst systems avoid formation of tartaric acid [133-37-9] and produce i j -epoxysuccinic acid [16533-72-5] at pH values above 5. The reaction of maleic anhydride and hydrogen peroxide in an inert solvent (methylene chloride [75-09-2]) gives permaleic acid [4565-24-6], HOOC—CH=CH—CO H (88) which is useful in Baeyer-ViUiger reactions. Both maleate and fumarate [142-42-7] are hydroxylated to tartaric acid using an osmium tetroxide [20816-12-0]/io 2LX.e [15454-31 -6] catalyst system (89). 

Other examples are the use of osmium(VIII) oxide (osmium tetroxide) as catalyst in the titration of solutions of arsenic(III) oxide with cerium(IV) sulphate solution, and the use of molybdate(VI) ions to catalyse the formation of iodine by the reaction of iodide ions with hydrogen peroxide. Certain reactions of various organic compounds are catalysed by several naturally occurring proteins known as enzymes. 

Epoxidation systems based on molybdenum and tungsten catalysts have been extensively studied for more than 40 years. The typical catalysts - MoVI-oxo or WVI-oxo species - do, however, behave rather differently, depending on whether anionic or neutral complexes are employed. Whereas the anionic catalysts, especially the use of tungstates under phase-transfer conditions, are able to activate aqueous hydrogen peroxide efficiently for the formation of epoxides, neutral molybdenum or tungsten complexes do react with hydrogen peroxide, but better selectivities are often achieved with organic hydroperoxides (e.g., TBHP) as terminal oxidants [44, 45],... 

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