Topic
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.
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TL;DR: In this paper, the authors observed octahedral aluminum species connected to the framework structure of zeolite Beta, and these aluminum sites exhibit characteristics of Lewis acid sites, which are created by partial hydrolysis of framework Si-O-Al bonds; they convert reversibly to tetrahedral aluminum sites upon aqueous NH+4 exchange or reaction with NH3 gas.
82 citations
Patent•
15 Oct 1973
TL;DR: In this article, high active, hydrothermally stable and ammonia-stable Y zeolite compositions are disclosed, which compositions are useful as adsorbents, hydrocarbon conversion catalysts, and as acidic supports for catalytic metals.
Abstract: Highly active, hydrothermally stable and ammonia-stable Y zeolite compositions are disclosed, which compositions are useful as adsorbents, hydrocarbon conversion catalysts, and as acidic supports for catalytic metals The stabilized Y zeolite composition is prepared from a sodium Y zeolite by a novel sequence of: (1) partial exchange of ammonium ions for sodium ions, (2) steam calcination under controlled conditions of time, temperature and steam partial pressure, and (3) further ion exchange of ammonium ions for sodium ions to reduce the final Na2O content to below about one weight-percent
82 citations
TL;DR: In this article, a small amount of noble metal (Pt, Rh or Pd) was added to the Fe-ZSM-5 catalyst to reduce the reaction temperature to 250-350 °C.
Abstract: We have reported previously the excellent performance of Fe-exchanged ZSM-5 for selective catalytic oxidation (SCO) of ammonia to nitrogen at high temperatures (e.g., 400-500 °C). The present work indicates that the reaction temperature can be decreased to 250-350 °C when a small amount of noble metal (Pt, Rh or Pd) is added (by both doping and ion exchange) to the Fe-ZSM-5. The SCO activity follows the order: Pt/Fe-ZSM-5 > Rh/Fe-ZSM-5 > Pd/Fe-ZSM-5. The noble metal promoted Fe-ZSM-5 catalysts also show higher activity for NH3 oxidation than Ce-exchanged Fe-ZSM-5 at low temperatures. On the Pt promoted Fe-ZSM-5, near 100% of NH3 conversion is obtained at 250 °C at a high space velocity (GHSV = 2.3 × 105 h-1) and nitrogen is the main product. The presence of H2O and SO2 decreases the SCO performance only slightly. This catalyst is a good candidate for solving the ammonia slip problem that plagues the selective catalytic reduction (SCR) of NO with ammonia in power plants.
82 citations
TL;DR: In this paper, a mechanistic model is presented, which combines the process of ammonia volatilization with the simultaneous transformation and movement of urea and its products in soil, for predicting the concentration profiles of Urea, ammoniacal-nitrogen and soil pH, and ammonia losses.
Abstract: SUMMARY
Urea application to soil raises the pH and ammonium concentration, thus providing ideal conditions for ammonia volatilization. A mechanistic model is presented, which combines the process of ammonia volatilization with the simultaneous transformation and movement of urea and its products in soil, for predicting the concentration profiles of urea, ammoniacal-nitrogen and soil pH, and ammonia losses, following application of urea.
The model consists of continuity equations describing the diffusion and reaction of urea, ammoniacal-nitrogen and soil base; it takes into account the volatilization of ammonia and the concurrent acidification of the soil surface; and considers a variable PCo2 profile due to soil respiration and urea hydrolysis. The derivation of the continuity equations and their boundary conditions, calculations of ammonia volatilization, and appropriate methods for numerical solutions are described.
82 citations
TL;DR: The kinetics of the interactions of aqueous ammonia with aqueously carbon dioxide/carbonate species has been investigated using stopped-flow techniques by monitoring the pH changes via indicators and a complete reaction mechanism has been established.
Abstract: The kinetics of the interactions of aqueous ammonia with aqueous carbon dioxide/carbonate species has been investigated using stopped-flow techniques by monitoring the pH changes via indicators. The reactions include the reversible formation of ammonium carbamate/carbamic acid. A complete reaction mechanism has been established, and the temperature dependence of all rate and equilibrium constants including the protonation constant of the amine between 15 and 45 °C are reported and analyzed in terms of Arrhenius, Eyring, and van’t Hoff relationships.
82 citations