Ammonia

About: Ammonia is a research topic. Over the lifetime, 16217 publications have been published within this topic receiving 271940 citations. The topic is also known as: NH3 & azane.

Chemical deactivation of V2O5/WO3–TiO2 SCR catalysts by additives and impurities from fuels, lubrication oils, and urea solution: I. Catalytic studies

Abstract: The influence of the combustion products of different lubrication oil additives (Ca, Mg, Zn, P, B, Mo) and impurities in Diesel fuel (K from raps methyl ester) or urea solution (Ca, K) on the activity and selectivity of vanadia-based SCR catalysts were investigated. Standard V2O5/WO3–TiO2 catalysts coated on metal substrates (400 cpsi) were impregnated with water soluble compounds of these elements and calcined at 400 and 550 °C, in order to investigate the chemical deactivation potential of different elements and combinations of them. It was found that potassium strongly reduced the adsorption equilibrium constant K N H 3 of ammonia. At small ammonia concentrations in the feed, only part of the active sites were covered with ammonia resulting in a reduced SCR reaction rate. At high ammonia concentrations, the surface coverage and SCR reaction rate increased, but high SCR activity at concurrent low ammonia emissions was impossible. Calcium caused less deactivation than potassium and did not affect the ammonia adsorption to the same extent, but it lowered the intrinsic SCR reaction rate. Moreover, deactivation by calcium was much reduced if counter-ions of inorganic acids were present (order of improvement: SO42− > PO43− > BO33−). Zinc was again less deactivating than calcium, but the positive effect of the counter-ions was weaker than in case of calcium. The degree of N2O production at T > 500 °C, which is typical for V2O5/WO3–TiO2 catalysts, was not influenced by the different compounds, except for molybdenum, which induced a small increase in N2O formation.

Nitrate and Nitrite Reduction

Abstract: Publisher Summary This chapter describes nitrate and nitrite reduction. Nitrate is the predominant form of nitrogen available to most cultivated plants grown under normal field conditions. Although ammoniacal fertilizers are used almost exclusively, the ammonia derived from these fertilizers is oxidized to nitrate by soil organisms. Nitrification is extremely rapid when the soil is well aerated, moist, and above 7°–10°C. Certain bacteria can utilize nitrate nitrogen as the sole nitrogen source for the synthesis of all nitrogen containing compounds of the cell. This nitrate assimilation can occur under both aerobic and anaerobic conditions. Nitrate reduction by partially purified enzyme preparations is frequently stimulated by phosphate. Nitrate reduction, mediated by either reduced pyridine nucleotides or reduced viologen dyes, is inhibited by cyanide and azide; however, pyridine-nucleotide-mediated reduction of cytochrome c is insensitive to these inhibitors. A reactivation of an inactive nitrate reductase apoenzyme extracted from molybdenum-deficient plants can be achieved by the addition of acid-treated nitrate reductase or by addition of phosphate buffer washes of nitrate reductase absorbed on adenosine monophosphate -Sepharose.