Hydrogen peroxide photolysis. Mechanism of photocatalytic effect of transition metals

1983 ◽  
Vol 48 (11) ◽  
pp. 3033-3040 ◽  
Author(s):  
Stanislav Luňák ◽  
Josef Vepřek-Šiška
Keyword(s):  
Hydrogen Peroxide ◽  
Reaction System ◽  
Transition Metal Ions ◽  
Thermal Reaction ◽  
Oxidation States ◽  
Photochemical Reduction ◽  
Photocatalytic Effect ◽  
Catalytically Active ◽  
Photochemical Decomposition ◽  
Catalytic Cycles

The photochemical decomposition of hydrogen peroxide depends on the presence of transition metal ions in the reaction system. Photochemical reduction of the poorly catalytically active ions with higher oxidation states produces catalytically active ions of lower oxidation states which catalyze the thermal reaction. The quantum yield of hydrogen peroxide photolysis is proportional to the number of catalytic cycles occurring on the photochemically generated catalyst.

Could Hydrogen Peroxide Photolysis Occur in the Absence of Transition Metals ?

1981 ◽  
Vol 36 (5) ◽  
pp. 654-655 ◽  
Author(s):  
Stanislav Luňák ◽  
Josef Vepřek-Šiška
Keyword(s):  
Hydrogen Peroxide ◽  
Transition Metal ◽  
Reaction System ◽  
Transition Metal Ions ◽  
Quantum Yields ◽  
Complexing Agents ◽  
Square Root ◽  
Catalytically Active ◽  
Active Transition ◽  
Trace Concentrations

Quantum yields of hydrogen peroxide photolysis increase with the square root of concentration of added Cu(II). The cupric ions are photo-catalytically active already at trace concentrations (10-7), i.e., at the concentrations present in any real reaction system. Hydrogen peroxide photolysis is completely suppressed on addition of complexing agents such as EDTA. It is believed that no hydrogen peroxide photolysis would occur in complete absence of photo-catalytically active transition metal ions

Photolysis of hydrogen peroxide, photocatalytic effects of Cu(II) and reaction kinetics

1986 ◽  
Vol 51 (5) ◽  
pp. 973-981 ◽  
Author(s):  
Stanislav Luňák ◽  
Petr Sedlák ◽  
Josef Vepřek-Šiška
Keyword(s):  
Hydrogen Peroxide ◽  
Thermal Decomposition ◽  
Quantum Yield ◽  
Reaction Kinetics ◽  
Copper Ions ◽  
Oxidation States ◽  
Radiation Temperature ◽  
Quantum Yields ◽  
High Quantum ◽  
Catalytically Active

The quantum yield of hydrogen peroxide photolysis has been measured as a function of the concentration of photocatalytically active Cu2+ ions, intensity of photolytic radiation, temperature, and hydrogen peroxide concentration. The results obtained are consistent with the concept that high quantum yields of hydrogen peroxide photolysis (Φ >> 1) are due to thermal decomposition of hydrogen peroxide catalyzed by photochemically generated copper ions in oxidation states which are catalytically active.

Oxidation of benzaldehyde by dioxygen. The thermal reaction

1982 ◽  
Vol 47 (2) ◽  
pp. 392-402 ◽  
Author(s):  
Pavel Lederer ◽  
Stanislav Luňák ◽  
Eva Mácová ◽  
Josef Vepřek-Šiška
Keyword(s):  
Catalytic Activity ◽  
Transition Metal ◽  
Transition Metal Complexes ◽  
Transition Metal Ions ◽  
Thermal Reaction ◽  
Oxidation States ◽  
Reaction Step ◽  
Free Radical Formation ◽  
Trace Concentrations ◽  
Lower Oxidation

The oxidation of benzaldehyde is catalyzed by transition metal ions even when these are present in trace concentrations. In complete absence of the ions, the reaction between benzaldehyde and dioxygen would not take place. A study has been made of the oxidation of benzaldehyde in benzene catalyzed by transition metal complexes. The catalytic activity of transition metals is higher when they assume their lower oxidation states. When the reaction is catalyzed by iron(III) bis(2,4-pentanedionato)-complex, the first reaction step is the reduction of Fe(III) to Fe(II), the latter being the catalyst of the thermal reaction. The mechanism proposed for the catalyzed reaction does not involve free radical formation.

Hydrogen peroxide decomposition on a two-component CuO-Cr2O3 catalyst

1988 ◽  
Vol 53 (8) ◽  
pp. 1636-1646 ◽  
Author(s):  
Viliam Múčka ◽  
Kamil Lang
Keyword(s):  
Hydrogen Peroxide ◽  
Catalytic Activity ◽  
Extreme Values ◽  
Catalytic Properties ◽  
Active Components ◽  
Catalytic Systems ◽  
Heterogeneous Catalytic ◽  
Peroxide Decomposition ◽  
Two Component ◽  
Catalytically Active

Some physical and catalytic properties of the two-component copper(II)oxide-chromium(III)oxide catalyst with different content of both components were studied using the decomposition of the aqueous solution of hydrogen peroxide as a testing reaction. It has been found that along to both basic components, the system under study contains also the spinel structure CuCr2O4, chromate washable by water and hexavalent ions of chromium unwashable by water. The soluble chromate is catalytically active. During the first period of the reaction the equilibrium is being established in both homogeneous and heterogeneous catalytic systems. The catalytic activity as well as the specific surface area of the washed solid is a non-monotonous function of its composition. It seems highly probable that the extreme values of both these quantities are not connected with the detected admixtures in the catalytic system. The system under study is very insensitive with regard to the applied doses of gamma radiation. Its catalytic properties are changed rather significantly after the thermal treatment and particularly after the partial reduction to low degree by hydrogen. The observed changes of the catalytic activity of the system under study are very probably in connection with the changes of the valence state of the catalytically active components of the catalyst.

Photochemical decomposition of t-butyl hydroperoxide; Photocatalytical effects of VO(II) and Co(III) 2,4-pentanedionates

1988 ◽  
Vol 53 (3) ◽  
pp. 497-505 ◽  
Author(s):  
Stanislav Luňák ◽  
Aleksandr I. Kokorin ◽  
Eva Mácová ◽  
Pavel Lederer
Keyword(s):  
Free Radical ◽  
Opposite Effect ◽  
Radical Intermediate ◽  
Butyl Hydroperoxide ◽  
Free Radical Intermediate ◽  
Catalytically Active ◽  
Photochemical Decomposition ◽  
Epr Signal

It has been found that [VO(acac)2] and [Co(acac)3] increase the rate of t-BuOOH photolysis, whereas [Fe(acac)3] has the opposite effect. Redox changes of the catalytically active [VO(acac)2] were followed using the EPR technique. An EPR signal from a free radical intermediate of photochemical decomposition of t-BuOOH was recorded, and the concentration of the intermediate was monitored during the reaction.

Photocatalytic Effect of Fe(III) on Oxidation of Two-Carbon Substrates Related to Natural Waters

1994 ◽  
Vol 59 (5) ◽  
pp. 1066-1076 ◽  
Author(s):  
Šárka Klementová ◽  
Dana M. Wagnerová
Keyword(s):  
Mathematical Model ◽  
Natural Waters ◽  
Substrate Oxidation ◽  
Quantum Yields ◽  
Ferric Ions ◽  
Photochemical Reduction ◽  
Photocatalytic Effect ◽  
Carbon Substrates ◽  
Glyoxalic Acid ◽  
The Common

The influence of ferric ions on photoinitiated reaction of dioxygen with two carbon organic acids, aldehydes and alcohols related to natural waters was demonstrated. Photocatalytic effect of ferric ions, i.e. photochemical reduction of Fe(III) as the catalyst generating step, has been found to be the common principal of these reactions. The overall quantum yields of the reactions are in the range from 0.3 to 1.2. A mathematical model designed for the mechanism of cyclic generation of catalyst in the singlet substrate oxidation by O2 was applied to the system glyoxalic acid + Fe(III); a fair agreement between the simulated and experimental kinetic curves was obtained. The experimental rate constant is 4.4 .10-4 s -1.

scholarly journals Au Modified F-TiO2 for Efficient Photocatalytic Synthesis of Hydrogen Peroxide

Molecules ◽  
2021 ◽  
Vol 26 (13) ◽  
pp. 3844
Author(s):  
Lijuan Li ◽  
Bingdong Li ◽  
Liwei Feng ◽  
Xiaoqiu Zhang ◽  
Yuqian Zhang ◽  
...  
Keyword(s):  
Hydrogen Peroxide ◽  
Reaction System ◽  
Reaction Medium ◽  
Pure Tio2 ◽  
H2o2 Production ◽  
Tio2 Photocatalyst ◽  
H2o2 Decomposition ◽  
Spin Resonance ◽  
Photocatalytic Synthesis

In this work, Au-modified F-TiO2 is developed as a simple and efficient photocatalyst for H2O2 production under ultraviolet light. The Au/F-TiO2 photocatalyst avoids the necessity of adding fluoride into the reaction medium for enhancing H2O2 synthesis, as in a pure TiO2 reaction system. The F− modification inhibits the H2O2 decomposition through the formation of the ≡Ti–F complex. Au is an active cocatalyst for photocatalytic H2O2 production. We compared the activity of TiO2 with F− modification and without F− modification in the presence of Au, and found that the H2O2 production rate over Au/F-TiO2 reaches four times that of Au/TiO2. In situ electron spin resonance studies have shown that H2O2 is produced by stepwise single-electron oxygen reduction on the Au/F-TiO2 photocatalyst.

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