Catalysis Today, Vol.340, 26-33, 2020
An overview on the use of adsorption and reactions of NO to probe (photocatalytic) TiO2
Studies of the adsorption and reactions of appropriate molecules are a valuable means to probe active surfaces. This overview deals with the use of nitrogen monoxide - a molecule that has less been utilized than some others as a surface probe - to investigate TiO2 and TiO2-containing materials, with or without photo-excitation. It shows that diverse information can be derived from: (1) the infrared spectra of adsorbed NO; (2) the isotopic exchange of (NO)-O-18; (3) the formation of N2O and N-2; (4) the use of NO (or (NO)-O-18) in oxidation reactions in place of O-2; and (5) the evaluation of the electron transfer to NO through density functional theory calculations, ultraviolet photoemission spectroscopy, and photoconductance measurements. Valuable knowledge may thus be potentially acquired on: the accessibility and reactivity of surface OH groups, the lability of surface O atoms, the self-cleaning efficacy, the environment and dispersion of TiO2 in composite materials, the existence of bandgap electronic states, and the electron transfer capacity, depending on the investigation technique employed, the conditions and the type of TiO2 sample.