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.

Urea thermolysis and NOx reduction with and without SCR catalysts

Abstract: Urea–selective catalytic reduction (SCR) has been a leading contender for removal of nitrogen oxides (deNOx) from diesel engine emissions Despite its advantages, the SCR technology faces some critical detriments to its catalytic performance such as catalyst surface passivation (caused by deposit formation) and consequent stoichiometric imbalance of the urea consumption Deposit formation deactivates catalytic performance by not only consuming part of the ammonia produced during urea decomposition but also degrading the structural and thermal properties of the catalyst surface We have characterized the urea thermolysis with and without the urea-SCR catalyst using both spectroscopic (DRIFTS and Raman) and thermal techniques (thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC)) to identify the deposit components and their corresponding thermal properties Urea thermolysis exhibits two decomposition stages, involving ammonia generation and consumption, respectively The decomposition after the second stage leads to the product of melamine complexes, (HNCNH)x(HNCO)y, that hinder catalytic performance The presence of catalyst accompanied with a good spray of the urea solution helps to eliminate the second stage In this work, kinetics of the direct reduction of NOx by urea is determined and the possibility of using additives to the urea solution in order to rejuvenate the catalyst surface and improve its performance will be discussed

Enabling electrochemical reduction of nitrogen to ammonia at ambient conditions through rational catalyst design

Abstract: Commercial design of a sustainable route for on-site production of ammonia represents a potential economic and environmental breakthrough. In an analogous process to the naturally occurring enzymatic mechanism, synthesis of ammonia could be achieved in an electrochemical cell, in which electricity would be used to reduce atmospheric nitrogen and water into ammonia at ambient conditions. To date, such a process has not been realized due to slow kinetics and low faradaic efficiencies. Although progress has been made in this regard, at present there exists no device that can produce ammonia efficiently from air and water at room temperature and ambient pressure. In this work, a scheme is presented in which electronic structure calculations are used to screen for catalysts that are stable, active and selective towards N2 electro-reduction to ammonia, while at the same time suppressing the competing H2 evolution reaction. The scheme is applied to transition metal nitride catalysts. The most promising candidates are the (100) facets of the rocksalt structures of VN and ZrN, which show promise of producing ammonia in high yield at low onset potentials.