Dimensionality and charge states in CeO2 surface defects: A theoretical analysis using reactivity/stability descriptors with NO as the test molecule

Abstract

Density functional calculations are used to compute reactivity/stability descriptors and electronic structure at point defects on CeO2 (111), i.e. oxygen vacancies with neutral and positive charge states as well as linear defects on CeO2 (331). Surface topology plays a fundamental role in the reactivity, stability, and magnetic behaviour of materials. CeO2 surface with VO0 is the most reactive but least stable, while the opposite behaviour is exhibited by CeO2 (111). No magnetic moment is obtained for pristine (111) and (331); however, a magnetic moment is obtained when VO is considered, being more significant for a neutral vacancy of about 2.1 μB. For VO0, a change from Ce+4 to Ce+3 is observed in atoms nearest to the vacancy, whereas this behaviour is not obtained with VO2+. Adsorption of NO molecule is considered as a test molecule due to its dipolar and paramagnetic nature. NO adsorption on all surfaces considered is not dissociative and energetically favourable. Adsorption on pristine (111) and (331) is characterised by a covalent interaction, while adsorption on (111) with VO shows short-range physisorption, predominantly dipolar, suggesting a Debye-type Van der Waals interaction. Reactivity is enhanced at (111), (331), and (111)+VO2+ by NO, while increased stability is observed at (111)+VO0. Reduction in bandgap and increase in magnetic moment are observed after NO adsorption in all studied substrates. Descriptors such as work function, ionisation potential, electron affinity, chemical hardness, magnetic moment, and electron localisation function analyse the reactivity of surfaces.