The dynamic behaviour of CH3OH and NO2 adsorbed on CeO2(111) studied by noncontact atomic force microscopy

Abstract

The adsorption and reaction of methanol(CH3OH) and nitrogendioxide (NO2) on CeO2(111) surfaces in different oxidation states were studied by noncontact atomic force microscopy (NC-AFM). AfterCH3OH exposure,surface oxygen defects without reconstruction of the surrounding oxygen atoms were healed by methoxyspecies (CH3O).Under a CH3OH atmosphere, a heterogeneous feature in the reactivity of surface oxygen atoms toCH3OH was observed by successive NC-AFM observation: new line defects ofoxygen were produced as a result of a chemical event. Successive NC-AFMmeasurements also revealed that oxygen vacancies on a slightly reducedCeO2(111) surface were healedby exposure to NO2. The contrast of healed oxygen defects in NC-AFM images was similar to that ofother surface oxygen atoms. This indicates that dissociative adsorption ofNO2 occurred at the defects. Nitrogen trioxide(NO3) was also observedon a slightly reduced CeO2(111) surface after NO2 exposure. On a CeO2(111) surface without surface oxygen defects, neither adsorption ofNO2 norformation of NO3 was observed. The reaction mechanisms for the formation of line defects andNO3 are discussed briefly.