Topic
Selective catalytic reduction
About: Selective catalytic reduction is a research topic. Over the lifetime, 10502 publications have been published within this topic receiving 226291 citations.
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TL;DR: In this paper, a NbOx/Ce0.75Zr0.25O2 (NbCZ) catalyst was synthesized by a citric acid-aided sol-gel method.
Abstract: A NbOx/Ce0.75Zr0.25O2 (NbCZ) catalyst was synthesized by a citric acid-aided sol-gel method. It shows that above 80% NOx conversion and above 95% N-2 selectivity for the selective catalytic reduction of NOx by ammonia over this catalyst are achieved in the temperature range 200-450 degrees C. Based on the DRIFTS and kinetic studies over NbCZ and Ce0.75Zr0.25O2, the promotion mechanism by niobia loading was elucidated with an overall reaction pathway. Two different reaction routes, "L-H" mechanism via "NH4NO3 + NO" at low temperatures ( 350 degrees C), are presented. The niobia addition increases the surface acidity and promotes the formation of nitrates species at low temperatures. In this way, the reaction between the ads-NH3 and nitrates species is accelerated to form NH4NO3 intermediates, which then decompose to N-2 and H2O. The reaction of the ads-NH3 species with gaseous NOx at high temperatures is also promoted due to the enhanced acidity and weakened thermal stability of nitrates after niobia loading.
112 citations
TL;DR: In this article, the selective catalytic reduction of NOx in the typical operation temperatures and oxygen concentrations of diesel engines has been studied in the presence of V3W9Ti in a tubular flow reactor.
112 citations
TL;DR: In this paper, the authors identify the active site for a given reaction from first-principles simulations of the total energy of Cu(II) ions in various positions in combination with previously published catalytic activity as a function of the copper exchange level.
Abstract: Recently, the outstanding properties of Cu-SSZ-13 (a zeolite in the chabazite structure) for the selective catalytic reduction of nitrous oxides were discovered. However, the true nature of the active site is still not answered satisfactorily. In this work, we identify the active site for the given reaction from first-principles simulations of the total energy of Cu(II) ions in various positions in combination with previously published catalytic activity as a function of the copper exchange level. This attribution is confirmed by the simulation of vibrational properties of CO adsorbed to the reduced Cu(I) species. The relation between energetic considerations, vibrational calculations, and experiment allows a clear statement about the distribution of active sites in the catalyst. We furthermore discuss the structural properties of the active site leading to the high stability under reaction conditions over a large temperature range. The insights from this work allow a more targeted catalyst design and rep...
112 citations
TL;DR: In this article, a mechanism for ammonia oxidation to nitrogen is proposed wherein part of the ammonia fed to the catalyst is converted into nitric oxide, and a pool of monoatomic surface nitrogen species of varying oxidation states is established.
112 citations
TL;DR: In situ EXAFS has been used to examine the hydrogen effect on the selective catalytic reduction of NOx over silver/alumina catalysts and the enhanced activity found in the presence of hydrogen is thought to be due to a chemical effect and not the result of a change in the structure of the active site.
Abstract: In situ EXAFS has been used to examine the hydrogen effect on the selective catalytic reduction of NOx over silver/alumina catalysts. For all SCR conditions used, with or without co-reductant (H2 or CO), the catalyst structure remained the same. Significant changes in the catalyst were only found under reducing conditions. The enhanced activity found in the presence of hydrogen is thought to be due to a chemical effect and not the result of a change in the structure of the active site.
112 citations