Photocatalytic Oxidation of NO₂ on TiO₂: Evidence of a New Source of N₂O₅

Abstract

N2O5 is an important intermediate in the atmospheric nitrogen cycle. Using a flow tube reactor, N2O5 was found to be released from the TiO2 surface during the photocatalytic oxidation of NO2, revealing a previously unreported source of N2O5. The rate of N2O5 release from TiO2 was dependent on the initial NO2 concentration, relative humidity, O2/N2 ratio, and irradiation intensity. Experimental evidence and quantum chemical calculations showed that NO2 can react with the surface hydroxyl groups and the generated electron holes on the TiO2, followed by combining with another NO2 molecule to form N2O5. The latter was physisorbed on TiO2 and had a low adsorption energy of −0.13 eV. Box model simulations indicated that the new source of N2O5 released from TiO2 can increase the daytime N2O5 concentration by up to 20 % in urban areas if abundant TiO2‐containing materials and high NOx concentrations were present. This joint experimental/theoretical study not only demonstrates a new chemical mechanism for N2O5 formation but also has important implications for air quality in urban areas.

An Alternative Calibration Method for Measuring N2O5 with an Iodide-Chemical Ionization Mass Spectrometer and Influencing Factors

“…An advantage of this technique is that it does not suffer from high and variable chemical interferences compared with TD-CIMS. In recent years, this method has been widely used to measure N 2 O 5 both in laboratory and field experiments ,− I − + N 2 O 5 → normalI ( normalN 2 normalO 5 ) − …”

Dissecting the Photochemical Reactivity of Metal Ions during Atmospheric Nitrate Transformations on Photoactive Mineral Dust

“…7 Chu et al revealed a new pathway for the oxidation of NO 2 to form N 2 O 5 on the TiO 2 surface. 11 In the case of metal ions, there is concern about their impact on human health due to their strong affinity to biological macromolecules. 12 As for source specificity of metal ions, it is often used to determine the origin of particulate pollution.…”

“…Ma et al found that TiO 2 could result in nitrate decomposition to yield higher reactive nitrogen species concentration than SiO 2 . Chu et al revealed a new pathway for the oxidation of NO 2 to form N 2 O 5 on the TiO 2 surface …”

Continuous NO Upcycling into Ammonia Promoted by SO2 in Flue Gas: Poison Can Be a Gift

“…As an important carrier of nitrogen energy, nitrogen oxide (NO) is predominantly utilized as an alternative precursor for ammonia (NH 3 ) synthesis to avoid dissociating the inert NN bond in N 2 molecules. − Since the 1990s, many advanced approaches, by the application of electro-, photo-, and plasmon-driven routes, have been developed to conduct the NO reduction reaction (NORR) for its value-added conversion under ambient conditions. − Although the NH 3 synthesis rate from NORR is significantly promoted in recent literature, − the key challenge still lies in that the conversion ratio of NO is far below practicability as a result of the ultralow solubility of NO in reaction solutions. Unlike harmless N 2 that is the feedstock for Haber–Bosch NH 3 synthesis, NO is one of the major air pollutants. − That is, the limited conversion ratio of the current NORR route would potentially contribute more to the emission of the contaminant than to its upcycling.…”