Catalyst amounts, hydrogen peroxide decomposition

The four curves show that various catalysts reduce the activation energy for the hydrogen peroxide decomposition reaction, but by different amounts. Notice that the enzyme catalase almost cancels the activation energy. 

The Influence of the Amount of Catalysts on the Hydrogen Peroxide Decomposition... 

By the presence of either HRP or apFe, the Bray-Liebhafsky reaction is changed in a similar manner. Some amounts of the mentioned catalysts influence decrease, whereas the other amounts influence increase of the characteristic periods Ti and Tend - In other words, some amounts of mentioned catalysts cause the acceleration of the reactions (R), (O), and (D), whereas the other amounts cause their inhibition. Anyhow, by the presence of either HRP or apFe in the BL reaction, the new reaction system for hydrogen peroxide decomposition is formed. 

Hydrogen peroxide decomposition catalysts can be added to ionomer membranes in small amounts to slow down the decomposition of the ionomer during fuel cell operation. Additions of cerium and manganese, in both oxide and ionic forms, have been shown to increase the oxidative stability of membranes by orders of magnitude, and fuel cells prepared with such membranes have shown substantial increases in hfetime under aggressive hot and dry operation [60-62]. Unfortunately, these metal ions and oxides can consume ion exchange capacity and negatively impact fuel cell performance. 

Hydrogen peroxide decomposition by Mn-tmtacn complexes in CH3CN was shown to be suppressed effectively by addition of oxalate [94d] or ascorbic acid [94a] as coepoxidation activity of the in situ prepared Mn-tmtacn complex [94d]. In general, fidl conversion was reached with less than 1 mol% of catalyst within 1 h. In addition to oxalic acid, several other bi- or polydentate additives, for example, diketones or diacids, in combination with Mn-tmtacn and H2O2 were found to favor alkene epoxidation over oxidant decomposition [94d]. Employing this mixed catalytic system, allylic alkenes (e.g., allyl... 

The second major discovery regarding the use of MTO as an epoxidation catalyst came in 1996, when Sharpless and coworkers reported on the use of substoichio-metric amounts of pyridine as a co-catalyst in the system [103]. A change of solvent from tert-butanol to dichloromethane and the introduction of 12 mol% of pyridine even allowed the synthesis of very sensitive epoxides with aqueous hydrogen peroxide as the terminal oxidant. A significant rate acceleration was also observed for the epoxidation reaction performed in the presence of pyridine. This discovery was the first example of an efficient MTO-based system for epoxidation under neutral to basic conditions. Under these conditions the detrimental acid-induced decomposition of the epoxide is effectively avoided. With this novel system, a variety of... 

FIGURE 13.33 A small amount of catalyst—in this case, potassium iodide in aqueous solution—can accelerate the decomposition of hydrogen peroxide to water and oxygen, (a) The slow inflation of the balloon when no catalyst is present, (b) Its rapid inflation when a catalyst is present. 

Small amounts of 02 can be prepared in the laboratory by electrolysis of water, by decomposition of aqueous hydrogen peroxide in the presence of a catalyst such as Fe3+, or by thermal decomposition of an oxoacid salt, such as potassium chlorate, KC103 ... 

Sometimes, a trace of a metal catalyst is required to affect very large amounts of reactants. For example, one ten-millionth of its mass of finely divided platinum is, however, needed to catalyse the decomposition of hydrogen peroxide. 

The ammoximation of cyclohexanone had been known before the discovery of TS-1, but the performances of conventional catalysts were far below the standards required for development work. In the EniChem process, the reaction is carried out in the liquid phase, at ca. 80°C, using a suspension of TS-1 in aqueous t-butanol, with a slight excess of hydrogen peroxide over the ketone. The substrate and the oxidant undergo total conversion with selectivities close to 98% and 94%, respectively. Inorganic by-products comprise minor amounts of ammonium nitrate and nitrite, N2O, and N2 produced by the oxidation of ammonia, and O2 by the decomposition of the oxidant. 

The catalytic activity of the components of the spinel system Cui.x x] Cr04 was studied for decomposition of hydrogen peroxide. 0.5ml of 30% H2O2 in 4.5 ml of distilled water was taken in flask, a 50 mg of the above catalyst was added. The flask was kept in constant temperature bath. The amount of oxygen liberated as a function of time was measured by downward displacement of water from the inverted burette. Burette was connected to reaction flask by rubber tubing. Each composition of the system was studied for the catalytic behaviour for three different temperatures. 

In both theories considered above, which have been current for many years, it will be seen that the decomposition of hydrogen peroxide into oxygen and water is always accompanied by the stoichiometric formation of the peroxidic intermediate or an equivalent amount of oxidation and reduction of the catalyst. However, from recent work it appears that this need not always be the case. Thus Haber and Willstatter (3) in a speculative paper, which attempted to explain certain aspects of some... 

Hydrogen peroxide (HY-druh-jin per-OK-side) is a clear, colorless, somewhat unstable liquid with a bitter taste. When absolutely pure, the compound is quite stable. Even small amounts of impurities (such as iron or copper), however, act as catalysts that increase its tendency to decompose, sometimes violently, into water and nascent oxygen (0). To prevent decomposition, small amounts of inhibitors, such as acetanilide or sodium stannate are added to pure hydrogen peroxide and hydrogen peroxide solutions. 

Another set of experiments was carried out with hydrogen peroxide. We previously showed that at 90°C, the hydrogen peroxide decreases the amount of coke as function of time (4). During the decomposition the hydrogen peroxide provides atomic oxygen, which in the presence of a metal oxide could accelerate the oxidation of the hydrocarbon deposits. However, at 50°C the amount of coke removed was rather low (result not shown). At 100°C, in a treatment carried out for 3.5 h, the coke was decreased from 13% to 8.5%, what is similar to the effectivity found on the LCH-Y catalyst without metal. 

When the catalytic activity of graphite modified with mixtures of different proportions of FeTSPc and CoTSPc was tested for ORR, it was found that the catalysts acted independently, that is, the amount of peroxide generated was directly proportional to the fraction of CoTSPc present on the electrode surface. FeTSPc did not promote the decomposition or reduction of peroxide generated on sites occupied by CoTSPc. However, the possibihty for the Fe centers to form hydrogen peroxide... 

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