Enhanced hydrogen formation during the catalytic decomposition of H2O2 on metal oxide surfaces in the presence of HO radical scavengers

Abstract

Presently and for the foreseeable future, hydrogen peroxide and transition metal oxides are important constituents of energy production processes. In this work, the effect of the presence of HO radical scavengers on the product yield from the decomposition of H2O2 on metal oxide surfaces in aqueous solution was examined experimentally. Scavenging the intermediate product HO˙ by means of Tris or TAPS buffer leads to enhanced formation of H2. In parallel, a decrease in the production of the main gaseous product O2 is observed. Under these conditions, H2 formation is a spontaneous process even at room temperature. The yields of both the H2 and O2 depend on the concentration of Tris or TAPS in the reaction media. We observed that TAPS has a higher affinity for the surface of ZrO2 than does Tris. The difference in adsorption of both scavengers is reflected by the difference in their influence on the product yields. The observed sensitivity of the system H2O2-ZrO2 towards the two different scavengers indicates that O2 and H2 are formed at different types of surface sites.

Surface reactivity of hydroxyl radicals formed upon catalytic decomposition of H2O2 on ZrO2

“…Although the addition of hydroxyl radical scavenger will lower the yield of O 2 in H 2 O 2 -ZrO 2 system, the influence in the present work is negligible as compared to significant amount of N 2 /air [22]. The pH was adjusted to 7.5 by HCl/NaOH after mixing Tris and ZrO 2 .…”

“…The mechanism of catalytic decomposition of H 2 O 2 on the surface of oxides can be concluded from previous works [17,18] and is summarized as follows: The produced intermediate radicals in (R1) and (R2) are bound to the oxide surfaces and for this reason, their half-lives may be prolonged significantly to several hours or even up to days [20,21]. It has been verified that the hydroxyl radical is the primary prod- [16,18,22]. HO • (ads) may react further on the interface, thereby affecting the whole system.…”

Removal of NOX Using Hydrogen Peroxide Vapor over Fe/TiO2 Catalysts and an Absorption Technique

“…Recent studies have proven that H 2 O 2 can act both as an oxidant and as a reductant via a redox path of Ti 3+ /Ti 4+ when the decomposition reaction of a H 2 O 2 molecule over a TiO 2 surface occurs [13]. It should be noted that defective surface sites, especially for the oxygen vacancies, play a significant role in the decomposition of H 2 O 2 [14]. However, the limited quantity of oxygen vacancies on a pure TiO 2 surface retards its capacity for the generation of •OH by activating H 2 O 2 .…”

An Overview of Interfacial Radiation Chemistry in Nuclear Technology

“…If the hydroxyl radicals were quantitatively scavenged by Tris, the production of molecular oxygen would be completely inhibited. In a recent study, the effect of scavenger concentration on the yield of molecular oxygen upon catalytic decomposition of hydrogen peroxide on ZrO 2 and TiO 2 was studied experimentally in non‐irradiated systems 13. This study clearly showed that the molecular oxygen yield decreased with increasing scavenger concentration, as expected from the reaction mechanism given above.…”