Creation of redox adsorption sites by Pd²⁺ ion substitution in nanoTiO² for high photocatalytic activity of CO oxidation, NO reduction, and NO decomposition

Abstract

The present study aims at developing a new photocatalyst for NO reduction and CO oxidation by creating redox adsorption sites and utilizing oxide ion vacancy in titania. For this purpose, Pd ion-substituted TiO₂, Ti_1-xPd_xO_2-δ, was synthesized for the first time by solution combustion method. The photocatalytic activity was investigated with increasing Pd substitution and the optimum concentration was found to be 1 atom % Pd ion in TiO₂. The reduction of NO was carried out both in the presence and in the absence of CO. Despite competitive adsorption of NO and CO on the Pd²⁺ sites, the reduction of NO was 2 orders of magnitude higher than unsubstituted TiO₂. High rates of photooxidation of CO with O₂ over Ti_1-xPd_xO_2-δ are observed at room temperature. It was shown that enhanced CO oxidation at Pd²⁺ ion site and O₂ or NO photo dissociation at oxide ion vacancy is responsible for the enhanced catalytic activity.