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.

Removal of NO from flue gases by absorption to an iron(ii) thiochelate complex and subsequent reduction to ammonia

Abstract: THE combustion of fossil fuels generates SO2 and NOX pollutants which cause acid rain and urban smog1 Existing flue-gas desulphurization scrubbers involve wet limestone processes which are efficient for controlling SO2 emissions but are incapable of removing water-insoluble nitric oxide The current technique for postcombustion control of nitrogen oxide emissions, ammonia-based selective catalytic reduction, suffers from various problems2,3, including poisoning of the catalysts by fly ash rich in arsenic or alkali, disposal of spent toxic catalysts and the effects of ammonia by-products on plant components downstream from the reactor To circumvent the need for separate schemes to control SO2 and NOX, we have developed an iron(ii) thiochelate complex that enhances the solubility of NO in aqueous solution by rapidly and efficiently absorbing NO to form iron nitrosyl complexes The bound NO is then converted to ammonia by electrochemical reduction, regenerating the active iron(ii) catalyst for continued NO capture Our results suggest that this process can be readily integrated into existing wet limestone scrubbers for the simultaneous removal of SO2 and NOX

Unified mechanistic model for Standard SCR, Fast SCR, and NO2 SCR over a copper chabazite catalyst

Abstract: Mechanistic proposals for the different SCR subreactions are integrated into one surface reaction mechanism that describes the main SCR reactions (Standard SCR, Fast SCR, NO2 SCR), transient effects due to nitrate storage, as well as the production of the side product N2O over a copper chabazite catalyst. The mechanism is parameterised to steady state and transient experiments, and is shown to predict the behaviour of the catalyst during a driving cycle, without any refitting of kinetic parameters. A dual site approach is used, where site 1 accounts for the adsorbed ammonia that forms on the Bronsted acid sites and copper ions, while site 2 is a copper ion (Cu2+-OH) where nitrites and nitrates are adsorbed. All main SCR reactions proceed via a reaction between ammonia and nitrites (ammonium nitrite pathway) to produce nitrogen; nitrites are also the linking species between the Standard SCR and NO oxidation reactions. Reactions between nitrates and ammonia to produce ammonium nitrate are also included, along with ammonium nitrate decomposition pathways (i.e., via NO addition to feed). Additionally, a global reaction taking place between adsorbed ammonia and gaseous NO2 to produce N2 at low temperatures ( The mechanism was used to analyse the importance of nitrate formation during a standard driving cycle. Surprisingly, although a significant amount of inhibitive ammonium nitrate is modelled to form during low temperature Fast and NO2 SCR steady state experiments, almost no ammonium nitrate is predicted to form during the driving cycle, thus allowing for a higher reaction activity than predicted based on steady state data. From a modelling and catalyst testing perspective, this shows the importance of capturing the catalyst’s transient behaviour rather than only steady state conditions, since steady state is not necessarily reached during practical driving scenarios.