H2O2 decomposition

HO- formation during H2O2 decomposition in the absence of the catalyst( ), in the presence of lOg 10wt% Cu/ Al203(A) and lOg copper plate(H). (The reactive dye was excluded in these experiments)... 

The first step, which is the slowest, limits the process and, hence, the rate of H2O2 decomposition is... 

The hot H3PO4 electrolyte rejects water, the reaction product. The high temperature favors H2O2 decomposition, and peroxide buildup is less pronounced than for the aqueous electrolyte systems. 

It is proposed that the oxidation reactions proceed through the formation of a surface peroxotitanate by interaction of framework Ti(IV) with H2O2, and the subsequent transfer of the oxygen from the peroxotitanate to the oxidizable organic products. The difference with respect to other Ti(IV) containing catalysts is attributed to the fact that in TS-1 all Ti(IV) are isolated from each other, with the consequence that the rate of H2O2 decomposition is reduced... 

Yields were improved by utilizing chemically modified charcoal [treatment with N,N-dimethylformamide dibutyl acetal (DMFBA) or N,0-bis(trimethylsilyl)acetamide (BSA)] due to suppression of H2O2 decomposition and ranged between 18 and 81%. Conversion and selectivity seem to depend extremely on the pre-treatment of charcoal with solutions of various pH values being highest for solutions with pH 7. 

Table 10. Relation between catalytic activity of H2O2 decomposition (given in time 50 [min] necessary for a decomposition of 50% H202) and dark conductivity of Co-polyphthalocyanines (from Ref. 5))...

E. coli catalase HPI haem B h2o2 decomposition porphyrin 3.1.1.3. 

Fenton reagent is simply due to the catalytic cycle of H2O2 decomposition, a process that generates HO radicals. 

Downes and Blunt H2O2 decomposition by sunlight Gmelin (1966) >... 

Kistiakowsky Effect of radiation on H2O2 decomposition Lunak and Sedlak (1992) >... 

Example 3-7 Calculate the amount of hydrogen peroxide that is theoretically decomposed by irradiation of its aqueous solution (V=l m ) within 1 h by a 10 kW medium-pressure mercury lamp that has a radiant power of 682 W at an active average wavelength X= (248 +253.7+ 265)/3 of 256 nm. The quantum yield of H2O2 decomposition equals 0.5 at 253.7 nm (Bolton and Cater, 1994). 

The hydroxylation of phenol on TS-1 is normally operated in a slurry reactor, at temperatures close to 100°C, with total consumption of the oxidant. The selectivities on phenol and H2O2 are generally in the ranges 90-95% and 80-90%, respectively. The hydroquinone to catechol ratio is well in excess of the statistical value of 1 2, owing to lower steric requirements for / -hydro-xylation and the faster diffusion of the p-substituted product (Table 2). Yields and kinetics are strictly related to the content of lattice Ti. It should be emphasized that any extra-framework Ti species, present as impurities on TS-1, are the major source of unproductive side reactions, such as H2O2 decomposition and unselective radical chain oxidations. 

The catalytic activities of Ti-MMM, Ti-SBA-15, and TS-1 are compared in Table XXXIII (234). The activities of these titanosUcates for MPS oxidation are in the order Ti-MMM > Ti-SBA-15 > TS-I. The catalytic activity was found to correlate with the rate of H2O2 decomposition in the absence of the organic reactant (Fig. 39). Ti-MMM on which H2O2 decomposed (to H2O and O2) faster (curve b) was also more active in the oxidation of the sulfur-containing compounds (Table XXXni). 

The free radicals ( OH, OOH,. ..) from H2O2 decomposition are a primary cause of membrane and ionomer chemical degradation. The H202-related membrane degradation mechanism will be discussed in more detail in section 12.3.1. The remainder of section 12.2 is divided into four subtopics anode, cathode, catalyst support, and engineered nanostructured electrodes. 

Limoges et al. looked at the HOR catalytic activities of a series of heteropolyacids (HPAs) containing Mo and V. The CD is too low (a few mA/cm ) for them to be used as stand-alone anode catalysts, although it should be pointed out that the HPA loading of the anode used in this study was one to two orders of magnitude lower on a molar basis than that of a typical Pt anode. However, HPAs have been shown to be promising proton-conductive membrane/ionomer tillers and effective catalysts for H2O2 decomposition. On this basis, they may eventually become a part of fuel cell electrodes. 

Characterization is a crucial step preliminary to any catalytic study, since the selectivity of the catalyst is strictly related to the position of Ti, in atomic dispersion, within the crystal lattice. Extra-framework Ti species, such as Ti02 particles and amorphous Ti-siUcates, indeed, promote H2O2 decomposition and radical chain oxidations. Normally, a combination of different techniques is necessary for reUable characterization, for example, UV-Vis, IR and Raman spectroscopies, XRD, EXAFS, XANES, TEM and SEM [8, 20]. Table 18.1 illustrates the main structural features of TS-1 and other Ti-zeoUtes relevant to this review. 

Ti—O is also an excellent candidate as an initiator of H2O2 decomposition (Scheme 18.20). The subsequent decomposition of H02 species into molecular oxygen could follow, at least in part, known pathways [1], The details of oxygen evolution, however, is an issue that goes beyond the scope of this chapter. 

Consistent with the general conditions that occur in flames, the HO2 formed by H atom diffusion upstream maximizes just before the reaction zone. H2O2 would begin to form and decompose to OH radicals. This point is in the 900-1000 K range known to be the thermal condition for H2O2 decomposition. As would be expected, this point corresponds to the rapid decline of the fuel mole fraction and... 

Based on these observations, Wang and Caruso [237] have described an effective method for the fabrication of robust zeolitic membranes with three-dimensional interconnected macroporous (1.2 pm in diameter) stmctures from mesoporous silica spheres previously seeded with silicalite-1 nanoparticles subjected to a conventional hydrothermal treatment. Subsequently, the zeolite membrane modification via the layer-by-layer electrostatic assembly of polyelectrolytes and catalase on the 3D macroporous stmcture results in a biomacromolecule-functionalized macroporous zeolitic membrane bioreactor suitable for biocatalysts investigations. The enzyme-modified membranes exhibit enhanced reaction stability and also display enzyme activities (for H2O2 decomposition) three orders of magnitude higher than their nonporous planar film counterparts assembled on silica substrates. Therefore, the potential of such structures as bioreactors is enormous. 

Salts of Ag(bpy)2l are reported to be effective catalysts for the H2O2 decomposition or persulphates Ag(bpy)2l salts are implicated in the process (621). 

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