CO Oxidation on Au Nanoparticles Supported on ZrO2: Role of Metal/Oxide Interface and Oxide Reducibility

In this paper, we report the results of density functional theory calculations on CO oxidation on a model Au/ZrO2 catalyst, in which the support is a non-reducible oxide (zirconia). Low-temperature CO oxidation on supported gold nanoparticles occurs through direct interaction of an activated O-2 molecule with adsorbed CO to form CO2. However, at room temperature or above the reaction follows another path as O-2 desorbs from Au at 170 K. On a reducible oxide, such as TiO2, CO is directly oxidized by a lattice oxygen in a gold-assisted Mars van Krevelen mechanism. The role of the oxide reducibility is thus essential, as the first step of the reaction is the formation of an oxygen vacancy. Contrary to what one would expect, the reaction can occur also on zirconia. We show that this is a result of the reduced oxygen vacancy formation energy at the gold/zirconia interface. The role of ambient oxygen is to reoxidize the support with a slightly activated process. The results point towards the importance of distinguishing between bulk reducibility and surface reducibility, as the latter can be strongly affected by phenomena such as deposition of metal nanoparticles or oxide nanostructuring.