Adsorption and Oxidation of NO₂ on Anatase TiO₂: Concerted Nitrate Interaction and Photon-Stimulated Reaction

Abstract

The catalytic and photon-induced oxidation of NO 2 on anatase TiO 2 has been studied and compared with the surface nitrate species obtained after adsorption of HNO 3 . Using a combination of in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), density functional theory (DFT), and temperature-programmed desorption (TPD), it is shown that identical products are obtained in all reaction systems but that their formation rates differ significantly. The surface reaction products are identified as combinations of surface−NO 3 − species, where NO 2 bonds to the lattice oxygen, and freely adsorbed NO 3 − ions. These products can be obtained either by dissociative adsorption of HNO 3 or by catalytic/photocatalytic oxidation of NO 2 , which is facilitated by UV light. A concerted reaction mechanism is unraveled that involves reorientation of bidentate nitrate that pushes out a neighboring protonated lattice oxygen to form a surface−NO 3 − species and a terminal OH group. The thermal stability of these surface species has been studied by means of TPD and simultaneous in situ DRIFTS measurements that reveal a main desorption peak (m/z = 46) at around 430 °C, which is attributed to concerted nitrate desorption through pentoxide (N 2 O 5 ) formation. A weaker and broader TPD peak is found at about 185 °C and is attributed to desorption of nitrate species bonded in a compressed configuration. The experimental results can be explained by the changing stability of the identified nitrate products, which depends strongly on the surface chemical environment and the surface coverage. The DFT results show that the stabilization of intermediate NO 2 adsorbates and the final nitrate reaction products occurs through a bifunctional charge exchange mechanism that is mediated by the TiO 2 crystal. In particular, a stable surface−NO 3 − and NO 3 − ion pair configuration has been identified. This mechanism explains both the thermal and photoinduced oxidation of NO 2 and their thermal stability and different formation rates, yielding high photoinduced oxidation reaction rates. Our results provide insights into the structure and chemical stability of nitrate surface products on TiO 2 particles and their formation mechanism, which is important for understanding their catalyzed transformation into the harmful compounds HONO and N 2 O during continued UV light illumination.

Reactive Adsorption of SO2 and NO2 Gases over Black Mass Derived from Discarded Alkaline Batteries

“…The surfacebound NO 2 − species could further react with the adsorbed NO 2 molecule to form surface-bound NO 3 − species and the NO gas molecule. 43 Thus, the reactive adsorption of NO 2 over the Ene_R surface yielded NO, NO 2 − , and NO 3 − species. The shift in the binding energy for the K 2p peak after NO 2 adsorption (291.8 → 292.2 eV) was due to the interaction of K + ions with the nitrite/nitrate ions (Figure S13a).…”

“…NO + further reacted with the lattice oxygen and transformed into surface-bound NO 2 – species. The surface-bound NO 2 – species could further react with the adsorbed NO 2 molecule to form surface-bound NO 3 – species and the NO gas molecule . Thus, the reactive adsorption of NO 2 over the Ene_R surface yielded NO, NO 2 – , and NO 3 – species.…”

Rapid Ozone Decomposition over Water‐activated Monolithic MoO3/Graphdiyne Nanowalls under High Humidity

“…Ground‐level ozone (O 3 ), as a greenhouse gas and secondary air pollutant, is harmful to the ecosystem and human health [1] . O 3 mainly originates from photochemical reactions among anthropogenic emission of volatile organic compounds (VOCs), nitrogen oxides (NO x ) in the presence of sunlight [2–4] . Trace O 3 is also detected from the widely used O 3 treatment process for sterilization in healthcare, food preservation and water quality treatment, etc., due to its strong germicidal ability [1,5–7] .…”

“…[1] O 3 mainly originates from photochemical reactions among anthropogenic emission of volatile organic com-pounds (VOCs), nitrogen oxides (NO x ) in the presence of sunlight. [2][3][4] Trace O 3 is also detected from the widely used O 3 treatment process for sterilization in healthcare, food preservation and water quality treatment, etc., due to its strong germicidal ability. [1,[5][6][7] However, the long-term exposure to even low concentration (100 ppb level, WHO guideline) of O 3 can do harm to pulmonary and cardiovascular system, and even lead to life expectancy decrease and death.…”

Selective Photocatalytic Reduction of 3‐Nitrophenol to 3‐Aminophenol by Anatase and Rutile TiO2 – What Stands Behind the Photoactivity?

“…In a controlled reaction environment, the most important factors that govern photocatalytic reactions at pristine TiO 2 materials have been discussed in numerous papers. For an individual phase, several intrinsic factors can be listed: crystal [1][2][3][4] and electronic structure, [5,6] surface area, [7,8] morphology and facet exposition, [9][10][11][12][13] surface species and adsorptivity, [14][15][16][17][18] charge lifetime and recombination rate, [19][20][21][22][23] as well as charge transfer efficiency. [24][25][26][27] On the other hand, the heterostructure of two polymorphs also plays a key role due to different possible reasons, including the band alignment, [28][29][30] phase junction, [31][32][33] and charge separation.…”