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• NO disproportionates on stoichiometric ceria to nitrites and trans -hyponitrites. • NO + O 2 coadsorption on ceria leads to formation of different surface nitrates. • NO interacts with reduced ceria forming NO2− and N 3 - species. • The NO2− species interact with NO to produce hyponitrites. • Azide species demonstrate properties very similar to those of surface isocyanates. Cerium is a key component in many DeNO x catalysts. An important property of ceria related to these applications is its high oxygen storage capacity. Indeed, in some reaction steps, cerium switches its oxidation state between 3+ and 4 +. To design new and effective cerium-based DeNOx catalysts, it is necessary to know in details the interaction between CeO 2-x and nitrogen oxides. One of the most informative techniques in this respect is IR spectroscopy. There are many IR studies devoted to this problem. However, as a rule, the efforts are concentrated on investigation of the oxidized forms of ceria and there are few works dealing with reduced oxide. There are also many contradictory assignments and few works use isotopic labelling for better interpretation of the spectra. Here we report a summary of our IR studies on the interaction of nitrogen oxides with ceria paying equal attention to the reduced and non-reduced oxide form. To strengthen the assignments we have used isotopically labelled molecules and DFT calculation. It was found that the initial stages of interaction of NO with oxidized ceria comprise NO disproportionation to symmetric nitrites (formal oxidation state of nitrogen 3+) and hyponitrites (formal oxidation state of nitrogen 1+). At further stages non-symmetric nitrites and N 2 O are also formed. In presence of oxygen all these species are converted into surface nitrates. Adsorption of N 2 O on reduced ceria is dissociative and leads to formation of N 2 with simultaneous filling the oxygen vacancies and oxidation of Ce3+. Initial stages of interaction of reduced ceria with NO includes (i) formation of surface azides (N 3 −, showing remarkable similarity with NCO− species) and NO2−. The latter species interact with additional NO molecule being thus converted into hyponitrites. Further stages are associated with formation of nitrites, and, in presence of O 2 , nitrates. [ABSTRACT FROM AUTHOR]

This study investigated nitrite (NO2−) accumulation due to FA (Free Ammonia: NH3) inhibition in an anaerobic-aerobic-anoxic (AOA) process reactor to mainly treat wastewater containing 302−610 mg/L of NH3/NH4+-N. Based on an experimental operation focusing on the nitrification, it was observed that NO2− was accumulated in the aerobic nitrification zone as pH increased, due to inhibition of NO2− conversion to NO3− by FA. This result implied FA inhibition to NOB (NO2−−Oxidizing Bacteria) for converting NO2− to NO3−. The objective of this study is to develop a feasible monitoring procedure for early detection of the FA inhibition toward NO2− accumulation and poor nitrification. Thus, in order to rapidly assess FA concentrations, an NH3 probe was utilized to measure NH3 concentrations together with applying a simple model prediction using the measured NH4+ concentrations, the Henry’s law constant of NH3 and measured pH. The predictive model NH3 levels were verified by a good correlation (89%) with the corresponding measured data, but the model prediction underestimated FA concentrations at less than 7.4 and a little overestimated at pH above 7.5. Interestingly, accumulated NO2− levels were roughly correlated with FA levels that were observed at delayed time points. This reflects the detected FA levels can be good indicators of NO2− levels with some delayed time. NO2− accumulation started at measured FA concentrations of higher than approximately 3 mg/L and ceased below that FA level. [ABSTRACT FROM AUTHOR]

[Display omitted] • When adsorbed on ceria NO initially disproportionates to nitrites and hyponitrites. • Further NO adsorption includes formation of non-symmetric nitrites and N 2 O. • Hyponitrites are very easily oxidized when dosing O 2 to the NO/CeO 2 system. • Nitrites first develop and are then oxidized when dosing O 2 to the NO/CeO 2 system. Adsorption of NO and co-adsorption of NO and O 2 on ceria have been re-investigated by FTIR spectroscopy. To provide unambiguous assignments of the IR bands, adsorption of 15NO and co-adsorption of 14NO + 15NO isotopic mixtures have also been studied and DFT calculations performed. At the initial adsorption stages mainly symmetric nitrite species (2472, 1304, ca. 1160 and 822 cm‐1) and trans- hyponitrites ([N 2 O 2 ]2−, ca. 1100 cm‐1) are simultaneously produced as a result of NO disproportionation. At further stages non-symmetric NO 2 − species (1393 and 1014 cm‐1), N 2 O (2240, 1252 cm‐1) and small amount of nitrates are formed. Nitrates are the only surface products of the thermal decomposition of the nitrites and hyponitrites. In the presence of small amounts of oxygen, the hyponitrites are very easily oxidized. In contrast, all nitrites increase in concentration after addition of small amount of O 2 to the NO/CeO 2 system but are gradually oxidized in the presence of higher amount of oxygen giving rise to different surface nitrates. [ABSTRACT FROM AUTHOR]

Support-free interconnected Pt nanowire networks (Pt NWNs) were fabricated by rapidly pouring sodium borohydride (NaBH4) solution into the Pt precursor solution, where hydrogen bubbles were in situ generated from hydrolysis and oxidation of NaBH4 as a dynamic template. There was no any capping agent, surfactant, seed, polymer, or special experimental device involved. The morphology, composition and structure of the samples were mainly characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). The architectures displayed highly electrocatalytic behavior toward nitrite oxidation and wide linear ranges of 1.0 μM-24.0 mM and 24.0-132.0 mM, together with high sensitivity (16.94 and 4.34 μA mM-1) and low detection limit (0.14 μM, S/N = 3). It demonstrated the improved electroanalytical performance for nitrite determination because of the unique free-standing Pt nanostructures with clean surfaces. [ABSTRACT FROM AUTHOR]

A method for the determination of nitrite in soil and vegetable samples by UV-Vis spectroscopy was proposed. The kinetic UV-Vis data were collected during the reaction between nitrite and 4-amino-3-hydroxynaphthalene-1-sulfonic acid with concentration of 0.001 M and pH 1.6. Data were collected by standard addition method. Multivariate curve resolution-alternating least squares was employed to analyze data with non-negativity and three-way data structure constraints. The method can be used to solve matrix effect and unknown interferents in the determination of nitrite in complex samples. The proposed method was used to determine nitrite at low mg/L levels with satisfactory results in soil, lettuce, cabbage and cucumber samples. [ABSTRACT FROM AUTHOR]