NO Adsorption And Reaction On Single Crystal Rutile TiO₂（110） Studied By UHV-FTIRS

With economic development, air pollution has attracted more and more attention in recent years. How to dissociate and remove various harmful gases from the atmosphere has been the primary issue for air pollution control. As an important component of the pollution gases, nitric oxide and its associated species mainly come from the petroleum products’ combustion processes. Nitric oxide reacts rapidly with oxygen and vapor to produce nitrogen dioxide, nitric acid and other corrosive substances. These nitrogen compounds are the main components of haze and cause significant damage to the metal frameworks of constructions and forest vegetation. How to effectively convert nitric oxide to innocuous species, i.e., N2 and O2, is an important subject. Under the promoting of governments, various efficient pollution reduction processes based on selective reduction catalysts were developed. As a kind of metal oxide, titanium dioxide (TiO2) is applied widely because of its high dielectric constant, efficient, nontoxic and good catalytic and photocatalytic properties. Among a variety of particles of oxide and metal co-doping, TiO2 showed excellent NO catalytic decomposition characteristics. In spite of its excellent catalytic properties, the mechanism of its catalysis is still not so clear. And model catalysis method, performed under ultrahigh vacuum (UHV) using surface science technologies, is the most efficient method to study the NO adsorption and catalytic reaction mechanism on TiO2.In this paper, in a new-designed state-of-the-art UHV-FTIR system, we studied NO adsorption and reactions using reflection-absorption infrared spectroscopy (RAIRS) on single crystal TiO2(110) surfaces under the ultrahigh vacuum (＜1×10-9mbar). We observed some intermediates of nitric oxide such as (NO)2 dimer and N2O on single crystal TiO2(110) surface, verified the bidentate symmetric structure of (NO)2 dimer on rutile TiO2(110) surface along the [001] direction, observed that the reaction (NO)2 →N2O can be induced by temperature, NO exposure amount and UV irradiation, respectively. All these verified the catalytic properties of rutile TiO2.In addition, through the co-adsorption of NO and CO on rutile TiO2(110) surface, we observed direct evidence of CO+NO→CO2+N2O reaction, induced by UV irradiation. Change the dosing sequence the competitive adsorption of CO, CO2, NO and N2O was also studied.