Healing of oxygen vacancies on reduced surfaces of gold-doped ceria

Abstract

Access to the full text of the published version may require a subscription. As an oxidation-reduction catalyst, ceria can catalyze molecular oxidation and reduction. There has been a focus on understanding and enhancing the vacancy formation process to improve the oxidative power of ceria. However, it is important to also address healing of the surface vacancy. To investigate healing of oxygen vacancies in ceria, we study the interaction of atomic and molecular oxygen and NO 2 with oxygen vacancies on gold-doped ͑110͒ and ͑100͒ surfaces using density functional theory, corrected for on-site Coulomb interactions ͑DFT+ U͒. For atomic and molecular oxygen, adsorption at the reduced surface is favorable and results in an oxygen atom sitting in an oxygen lattice site, healing the oxygen vacancy. On undoped surfaces, O 2 adsorbs as a peroxo ͑O 2 2− ͒ species. However, on the doped ͑110͒ surface a superoxo ͑O 2 − ͒ species is present. When NO 2 adsorbs ͑exothermically͒ at a divacancy surface, one oxygen of the molecule sits in the vacancy site and the N-O distances are elongated and an ͓NO 2 ͔ − anion forms, similar to the undoped surface. Vacancy healing of ceria surfaces is favorable, even if vacancy formation is enhanced, justifying the current focus on improving the oxidative power of ceria. We briefly examine a catalytic cycle: the reaction of CO with adsorbed O 2 on the undoped and doped surfaces, and find that the doped ͑110͒ surface facilitates CO oxidation. Rights

Synergy between gold and oxygen vacancies in gold supported on Zr-doped ceria catalysts for the CO oxidation

“…Some authors have established that oxygen vacancies can act as preferential structural sites for the selective deposition of gold, which would increase the dispersion of the noble metal [45,[48][49][50][51]. The interaction of the oxygen vacancies in CeO 2 with other metals such as Rh, Ir, Pd and Pt has been also observed and associated to a metal-support strong interaction model, named metal nesting, by the filling of the oxygen vacancies with the metallic atoms [52].…”

Periodic trends of oxygen vacancy formation and C–H bond activation over transition metal-doped CeO2 (1 1 1) surfaces

“…Similarly to the experimental studies, some of the dopants that have been thoroughly examined are Au [20,22,23], Cu [3,24,26], Pd [3,21,25,[27][28][29], and Zr [1,16,34,35], with concentration on surface reducibility as well as CO, CH 4 , H 2 , or H 2 O interactions with the surface. Using Au as a dopant in the CeO 2 lattice for CO oxidation allows the surface oxygen atoms to become reactive, but not too reactive that the oxygen vacancies will not heal.…”

“…The dopant metal may either alter the reducibility of the ceria metal atoms or the dopant can become the reduction center [14][15][16][17]. Several experimental [8][9][10][11][12][13]18,19] and theoretical studies [1][2][3][20][21][22][23][24][25][26][27][28][29] have examined how one or two transition metal dopants can affect the activity of the ceria surface; however, an electronic level explanation remains incomplete. For example, density functional theory (DFT) studies have demonstrated that Pd becomes the reduction center for O-vacancy formation or methane conversion when doped into CeO 2 [27][28][29][30].…”

Charge Compensation and Ce3+Formation in Trivalent Doping of the CeO2(110) Surface: The Key Role of Dopant Ionic Radius

“…Recent work indicates that healing of the vacancy with gas phase oxygen 11,17 or with NO 2 18,19 is favourable so that the determining step is the initial removal of the oxygen vacancy. The formation energy of oxygen vacancy in bulk CeO 2 is ca.4.5 eV 20,22 .…”