The role of Au and Pd in photocatalytic activation of molecular oxygen: A mechanistic study

Activation of molecular oxygen plays an important role in photocatalytic selective oxidation reactions and complete degradation of organic pollutants. Noble metal cocatalysts are often employed to modulate the activation of oxygen to reach an optimum photocatalytic performance. However, the role of the metal nanoparticles (NPs) still remains unclear and deserves investigation for the design of efficient photocatalysts. Here, Au and Pd NPs are deposited on the TiO₂ photocatalyst to study the promotional mechanism of O₂ dissociation with the presence of glycerol under irradiation by near-ambient-pressure photoelectron spectroscopy and in-situ spectrometry approaches. While both Au and Pd NPs can dissociate O₂ into activated oxygen species, a relatively strong bonds of dissociated oxygen atom is observed on Au NPs than on the Pd NPs. This results in a moderate reduction rate of O₂ and eventually favors a mild oxidation reaction process for Au, and a rapid reduction rate of O₂ and eventually a deep oxidation reaction process for Pd, respectively.