NOx

About: NOx is a research topic. Over the lifetime, 26367 publications have been published within this topic receiving 496555 citations.

First measurements and modeling of Δ17O in atmospheric nitrate

Abstract: [1] Atmospheric nitrate is anomalously enriched in both the 18O/16O and 17O/16O isotopic ratios, with Δ17O = 20–30.8‰ (Δ17O = δ17O − .52 × δ18O). We have modeled the seasonal variation in Δ17O by utilizing the transfer of Δ17O from ozone to HNO3 during NOx oxidation reactions and by evaluating the relative source strengths of heterogeneous and homogenous HNO3 production. The implications for new insights into the global nitrogen cycle, N2O production and paleoclimate studies are discussed.

Identification of the active sites on CeO2–WO3 catalysts for SCR of NOx with NH3: An in situ IR and Raman spectroscopy study

Abstract: A series of CeO2–WO3 (WxCe) catalysts were prepared for the SCR of NOx with NH3. Among the three representative samples, the W1Ce catalyst exhibited great activity during SCR reaction and a large amount of N2 from NH3 oxidation, whereas the W0.05Ce catalyst yielded more NO from NH3 oxidation than the W3Ce at high temperature. Three types of metal oxide species (isopolytungsten species, Ce2(WO4)3 compounds and crystalline WO3) were observed on the catalyst surfaces with increased WO3 loading. CeO2, rather than WO3 or Ce2(WO4)3, presented favorable reducibility behavior. Furthermore, CeO2 with intrinsic oxygen vacancies and unsaturated Wn+ cations of crystalline WO3 provided Lewis acid sites; meanwhile, the W O W or W O modes of Ce2(WO4)3 provided Bronsted acid sites. Based on the Raman spectra, the W O species of the [WO4] or [WO6] units could be the active sites. The results suggest a reaction mechanism consisting of two independent cycles, denoted as a redox cycle due to the excellent oxygen storage capability and reducibility of cubic fluorite CeO2 (for NH3 activation) and an acid site cycle, resulting from Bronsted acid sites formed on the W O W species of Ce2(WO4)3 (for NH3 adsorption). Surface nitrate species cannot be involved directly in SCR reaction with gaseous NH3; additionally, the adsorbed NO2 demonstrated activity over the W1Ce catalyst at 200 °C.

Mechanistic Aspects of deNOx Processing over TiO2 Supported Co–Mn Oxide Catalysts: Structure–Activity Relationships and In Situ DRIFTs Analysis

Abstract: Anatase TiO2-supported manganese and cobalt oxide catalysts with different Co/Mn molar ratios were synthesized by a conventional impregnation method and used for selective catalytic reduction (SCR) of NOx with NH3. The catalysts were characterized by N2 adsorption/desorption, X-ray diffraction, X-ray photoelectron spectroscopy, and temperature-programmed desorption with NH3 and NOx. Characterization of the catalyst confirmed that by using Co3O4 over Mn/TiO2, we enhanced NO oxidation ability. From in situ diffuse reflectance infrared transform spectroscopy (DRIFTs) analysis of desorption and the transient reaction, we concluded that the addition of Co could remarkably lower the activation energy of NOx chemisorption on the catalyst surface. In addition, low-temperature SCR activity mainly results from a “fast SCR” reaction. We observed four NOx species (bidentate nitrates, gaseous NO2, linear nitrites, and monodentate nitrites) on the surface of Mn/TiO2 and Co–Mn/TiO2 catalysts that all participated in the...