Oxygen-Vacancy-Stabilized Positively Charged Au Nanoparticles on CeO2(111) Studied by Reflection−Absorption Infrared Spectroscopy

Abstract

To examine the active form of Au on Au/CeO2 catalysts in the low-temperature water−gas shift (WGS) reaction, the effect of surface oxygen vacancies on CeO2(111) on the charged state of Au nanoparticles (or clusters) deposited at 85 K was studied by combination of structural investigation by scanning tunneling microscopy (STM) and charged state estimation by reflection−absorption infrared spectroscopy (RAIRS) using CO molecule as a probe. On a stoichiometric CeO2(111) without oxygen vacancies, only neutral Au species, which gave a ν(CO) peak at ∼2100 cm−1 for bound CO, were observed independent of preannealing temperatures up to 400 K. Introduction of surface oxygen vacancies by the electron stimulated desorption (ESD) process showed the majority of Au deposited at 85 K was positively charged, giving ν(CO) peaks at approximately 2130 and 2145 cm−1 bound to positively charged Au at different degree. Thermal stability measurements for the species in vacuum revealed that less positively charged Au species rem...