Thermal and photochemical reactions of NO2 on chromium(iii) oxide surfaces at atmospheric pressure

Abstract

While many studies of heterogeneous chemistry on Cr 2 O 3 surfaces have focused on its catalytic activity, less is known about chemistry on this surface under atmospheric conditions. We report here studies of the thermal and photochemical reactions of NO 2 on Cr 2 O 3 at one atm in air. In order to follow surface species, the interaction of 16-120 ppm NO 2 with a 15 nm Cr 2 O 3 thin film deposited on a germanium crystal was monitored in a flow system using attenuated total reflectance (ATR) coupled to a Fourier transform infrared (FTIR) spectrometer. Gas phase products were monitored in the effluent of an B285 ppm NO 2 -air mixture that had passed over Cr 2 O 3 powder in a flow system. A chemiluminescence NO y analyzer, a photometric O 3 analyzer and a long-path FTIR spectrometer were used to probe the gaseous products. In the absence of added water vapor, NO 2 formed nitrate (NO 3 À ) ions coordinated to Cr 3+ . These surface coordinated NO 3 À were reversibly solvated by water under humid conditions. In both dry and humid cases, nitrate ions decreased during irradiation of the surface at 302 nm, and NO and NO 2 were generated in the gas phase. Under dry conditions, NO was the major gaseous product while NO 2 was the dominant species in the presence of water vapor. Heating of the surface after exposure to NO 2 led to the generation of both NO 2 and NO under dry conditions, but only NO 2 in the presence of water vapor. Elemental chromium incorporated into metal alloys such as stainless steel is readily oxidized in contact with ambient air, forming a chromium-rich metal oxide surface layer. The results of these studies suggest that active photo-and thermal chemistry will occur when boundary layer materials containing chromium(III) or chromium oxide such as stainless steel, roofs, automobile bumpers etc. are exposed to NO 2 under tropospheric conditions.

SWCNT-aminopolymer composites on mesoporous alumina for fast, room-temperature detection of ultra-low concentrations of NO2 by mediation of water vapour

“…When water was removed (by evacuation and heating), the water solvated nitrate converted back to oxide-coordinated nitrate. Existence of such mechanisms on oxide surfaces, including that of Al 2 O 3 [36,37,39] and on diamond surfaces [40] have been confirmed by recent studies. It is conceivable that such a mechanism exists under our experimental conditions where the NO 3 adsorbed on the SWCNT-polymer is first converted to solvated nitrate ions on alumina surface in high humidity (∼60% used here) as observed on the oxide surfaces.…”

Green Synthesis of N/Zr Co-Doped TiO2 for Photocatalytic Degradation of p-Nitrophenol in Wastewater

“…The spectra undoubtedly reveal the presence of synthetic residues in addition to TiO 2 . For pure TiO 2 and TiO 2 /Zr2.8 samples, the doublet peaks located at 1553 cm −1 and 1315 cm −1 would seem to be attributed to nitrates [46][47][48], as well as the peak located at 1049 cm −1 which returns to the free NO 3 − ions [49,50]. In fact, pure and single Zr-doped samples (prepared in the presence of HNO 3 during the synthesis) often contain residues of NO 3…”

Heterogeneous chemistry and photochemistry of atmospherically relevant gases on oxide surfaces

“…Experimental studies have shown the conversion of oxide coordinated nitrate formed by NO 2 reacting with water solvated nitrate after exposure to water vapor on several different metal oxide surfaces including TiO 2 . 162,163,168 The structure of solvated nitrate or nitrate water clusters (NO 3 -…”

“…218 Additionally, some recent studies on NO 2 adsorption and photochemistry on semiconductor metal oxides such as Cr 2 O 3 and TiO 2 have shown conversion of adsorbed nitrate to gas-phase NOx species under irradiation conditions. 23,100,168 These studies used chemiluminescence, mass spectrometry and infrared spectroscopy as tools to detect gas-phase photoproducts and infrared spectroscopy and X-ray photoelectron spectroscopy to detect adsorbed photoproducts as well. For adsorbed species, it is sometimes difficult to differentiate products due to the fact that there are overlapping absorption bands for different species that contain N-O functional groups.…”

“…Fe dissolution from iron-containing atmospheric particles has received much attention recently due to atmospheric aging is thought to play a role. 168 In this study, photochemistry of adsorbed nitrate on hematite, -Fe 2 O 3 surface is investigated under environmentally relevant relative humidity and molecular oxygen by XPS and FTIR spectroscopic techniques. The impact that this reaction has on iron dissolution is also investigated.…”