Catalysts, hydrogen peroxide formation study

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. 

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... 

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],... 

Oxidation of thiophene and its derivatives was studied using hydrogen peroxide (H2O2), t-butyl-hydroperoxide and Ti-Beta redox molecular sieve as selective oxidation catalysts. A new reaction pathway was discovered and investigated using C-13 NMR, GC, GC-MS, HPLC, ion chromatography, and XANES. The thiophene oxidized to thiophene-sesquioxide [3a,4,7,7a-tetrahydro-4,7-epithiobenzo[b]-thiophene 1,1.8-trioxide] and the sesquioxide oxidized mostly to sulfate. 2-Methyl-thiophene and 2,5 dimethylthiophene also oxidized to sulfate and sulfone products. The Benzothiophene oxidation product was sulfone. This proposed new reaction pathway is different from prior literature, which reported the formation of thiophene 1,1-dioxide (sulfone ) as a stable oxidation product... 

The reaction with CoII(ACAC)2 was studied in more detail and the rate law was established. The reaction was found to be first-order with respect to the substrate and the catalyst concentrations, and the partial pressure of 02. The corresponding kinetic model postulates reversible formation of a H2DTBC-Con(ACAC)2 02 adduct which undergoes redox decomposition in the rate-determining step. Hydrogen peroxide is also a primary... 

Metal ion catalyzed autoxidation reactions of glutathione were found to be very similar to that of cysteine (76,77). In a systematic study, catalytic activity was found with Cu(II), Fe(II) and to a much lesser extent with Cu(I) and Ni(I). The reaction produces hydrogen peroxide, the amount of which strongly depends on the presence of various chelating molecules. It was noted that the catalysis requires some sort of complex formation between the catalyst and substrate. The formation of a radical intermediate was not ruled out, but a radical initiated chain mechanism was not necessary for the interpretation of the results (76). 

Rauhut and coworkers were the first to obtain rate constants from emission kinetic studies and to verify the dependence of kobsi and kobsi on the concentration of the base catalyst and on hydrogen peroxide, respectively. Schowen and coworkers , using TCPO, H2O2 and DPA, with triethylamine as catalyst, observed an oscillatory behavior in emission experiments and proposed a mechanism involving the formation of two HEIs (involved in parallel chemiluminescent reactions) to explain it. Other authors have also observed a similar oscillating behavior but have explained it as a complex... 

One-step electrophilic hydroxylation of aromatic compounds using various peroxide reagents in the presence of acid catalysts has been achieved. The systems studied include hydrogen peroxide in the presence of sulfuric acid,766 hydrogen fluoride,767 Lewis acids,768 769 and pyridinium poly(hydrogen fluoride).770 Lewis acid-promoted electrophilic hydroxylation with peracids,771,772 di-tcrt-butyl peroxide,773 and diisopropyl peroxydicarbonate774 775 were also described. A common feature of these reagents is the formation of monohydroxylated compounds in low yields. 

Various studies and some patents have been published on the use of membrane catalysts for the direct synthesis of H202 [73-81]. The redox treatment of the membrane influences the properties both in the synthesis and decomposition of H202. Formation of a hydrophobic layer improves the selectivity, because it limits the consecutive decomposition of hydrogen peroxide, limiting the chemisorption of H2 and re-adsorption of H202 [73]. Either polymeric or ceramic-type membranes could be used, but the latter are preferable to allow more robust operations. The mono- or bi-metallic Pd-based active component could be deposited either in the form of dispersed particles (e.g., by precipitation-deposition) or of a thin film (e.g., by... 

In laboratory studies, Ravikumar and Gurol [46] monitored the Fenton degradation of pentachlorophenol (PCP) and trichloroethylene (TCE) from sand. In both column and batch studies, they observed the degradation of PCP and TCE with the addition of hydrogen peroxide only. They concluded that iron naturally present in the sand was an effective catalyst for the formation of hydroxyl radical from the added peroxide. However, addition of soluble ferrous salts caused a more rapid degradation of the pollutants, indicating that either insufficient iron was present in the sand or the nature of the iron in the sand made it a poor catalyst. 

Although the authors in this sand study reported the iron content of the sand, there remains a possibility that noniron species were acting as catalysts. In fact, a study of coal (anthracite) oxidation by hydrogen peroxide indicates that formation of hydroxyl radical occurs even after the removal of iron from the coal [47], This study suggested that surface sites on the coal may have acted as catalytic centers for hydroxyl radical formation. Whereas coal is... 

Reaction 2 has been studied in great detail (28-441 since Baur and Neuweiler (28) in 1927 observed the formation of H202 when they illuminated aqueous zinc oxide suspensions in the presence of glycerin and glucose which in turn were oxidized. Appreciable yields of hydrogen peroxide are detected only when appropriate electron donors, D, are added prior to illumination. This strongly indicates that it is the electron donor, D, which is adsorbed on the catalyst s surface and hence sacrificed via Reaction 4. 

Methyl trioxorhenium (MTO) has proven to be an efficient catalyst in the presence of hydrogen peroxide, which leads to the formation of mono- and bisperoxo compounds an additional aquo ligand has been found to stabilize the latter complex. MTO as well as the corresponding monoperoxo- and bisperoxo complexes have been studied, in both their free and monohydrated forms.96... 

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