Photocatalytic Oxidation of CO on TiO₂: Chemisorption of O₂, CO, and H₂

Abstract

On the surface: Adsorption of O(2) at the surface oxygen vacancy (SOV) sites of TiO(2) reconstructs the lattice oxygen (healing SOVs), resulting in a decrease of the photocatalytic activity of oxidizing CO over vacuum-pretreated TiO(2) with increasing temperature (see scheme). Adsorption of H(2) produces new SOVs at the TiO(2) surface and stabilizes the photocatalytic activity. Photocatalytic oxidation of CO over vacuum-pretreated TiO(2) is performed in a series of systems with the introduction of O(2), CO, and H(2) in different orders. The photocatalytic oxidation of CO is dependent on the order of introduction of O(2), CO, or H(2), and introducing O(2) prior to CO promotes the oxidation of CO. Moreover, an increase of reaction temperature suppresses the oxidation of CO, but the preintroduction of H(2) reduces this suppression effect. The results of the chemisorption of O(2), CO, and H(2) at the TiO(2) surface reveal that the adsorbed O(2) heals the surface oxygen vacancy (SOV) sites of TiO(2), while the adsorbed CO and H(2) promote the formation of new SOVs. It is proposed that changes in the amounts of adsorbed O(2) and SOVs are mainly responsible for the differences of CO conversion in different systems.

Improved photoelectric properties of BiOBr nanoplates by co-modifying SnO2 and Ag to promote photoelectrons trapped by adsorbed O2

“…The improved O 2 adsorption favors the trapping of photoelectrons, leading to the enhanced SPS signals and charge separation. This is further confirmed by using a model reaction of photocatalytic CO oxidation [30]. In Fig.…”

Selective photocatalytic conversion of methane into carbon monoxide over zinc-heteropolyacid-titania nanocomposites

“…CO 2 is mostly produced as a secondary product of methane photo-oxidation over the zinc-containing catalysts. The mechanism of the CO total oxidation to CO 2 over TiO 2 has been investigated in several previous reports 56–58 . Linsebigler et al 57,58 have reported that the reaction proceeds over on vacancy defect sites on the TiO 2 surface and involves O 2 − surface species.…”

Promotion effect of ultraviolet light on NO + CO reaction over Pt/TiO2 and Pt/CeO2–TiO2 catalysts

“…As seen inFig. 11a, for Pt/TiO 2 adsorbing CO in dark (curve A), the peak at 1645 cm −1 (assigned to the H 2 O chemisorbed at the TiO 2 sites) and three peaks at 1443, 1413 and 1343 cm −1 (assigned to the different carboxylate-like species) are observed[35][36], which can be can be ascribed to the result of the adsorbed CO at TiO 2 sites reacting with the adjacent lattice oxygen of TiO 2[35]. Under UV irradiation (curve B inFig.…”

“…Under UV irradiation (curve B inFig. 11a), the increased peak at 1645 cm −1 and the decreased peaks at 1443 and 1413 cm −1 mean that UV light can promote the carboxylate-like species at TiO 2 sites to react with the surface hydroxyls over Pt/TiO 2 (resulting in the formation of H 2 O[35]). For Pt/CeO 2 -TiO 2 adsorbing CO in dark (curve C inFig.11), two observed broad peaks at 1500 and 1414 cm −1 can be assigned to the carboxylate-like species at CeO 2 or TiO 2 sites[37].…”