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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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Journal ArticleDOI
TL;DR: In this article, three options for removal of N 2 O using a promoted Fe-ZSM-5 catalyst have been explored under conditions representative for the off gases of a nitric acid plant: catalytic decomposition and selective catalytic reduction (SCR) using propane or methane as a reductant.
Abstract: Three options for removal of N 2 O using a promoted Fe-ZSM-5 catalyst have been explored under conditions representative for the off gases of a nitric acid plant: catalytic decomposition and selective catalytic reduction (SCR) using propane or methane as a reductant. Catalytic decomposition of N 2 O takes place at temperatures above 400°C at a space velocity of 10,000 h −1 . The addition of propane lowers the temperature for N 2 O conversion with about 100°C. In propane-assisted SCR of N 2 O, the emissions of unreacted hydrocarbons and of CO are low and also NO x reduction takes place. Methane is more difficult to be activated by the catalyst, which causes lower N 2 O destruction efficiency and the output of unreacted methane. In all cases, N 2 O conversion is higher at elevated pressure.

77 citations

Patent
17 Aug 1993
TL;DR: In this article, the NOx content in a flow of flue gas is reduced by passing the gas through a first treatment zone and a second treatment zone, where a nitrogeneous treatment agent is introduced into the first treatment zones for the selective non-catalytic reduction of part of NOx.
Abstract: The NOx content in a flow of flue gas is reduced by passing the flue gas through a first treatment zone and a second treatment zone. A nitrogeneous treatment agent is introduced into the first treatment zone for the selective non-catalytic reduction of part of the NOx, and the flue gas is thereafter passed through the second treatment zone which includes a catalyst for further selective catalytic reduction of the NOx. Optionally, a second nitrogeneous treatment agent is added to the flue gas in the second treatment zone. The quantity of NOx in the flue gas is detected intermediate the first and second treatment zones and, optionally, after the flue gas has left the second treatment zone. The quantity of ammonia in the flue gas exiting from the second treatment zone is also detected. The amounts of the treatment agents added to the flue gas are controlled responsive to the variations and absolute levels determined by these measurements.

77 citations

Journal ArticleDOI
TL;DR: In this paper, the authors developed novel hollandite Mn-Ti oxide promoted Cu-SAPO-34 catalysts (HMT@Cu-S) for the selective catalytic reduction of NOx with NH3 via the isolation of active sites and alkali metal trapping sites.
Abstract: Improved NOx reduction in the presence of alkali metals is still challenging. In this work, we developed novel hollandite Mn–Ti oxide promoted Cu-SAPO-34 catalysts (HMT@Cu–S) for the selective catalytic reduction (SCR) of NOx with NH3via the isolation of active sites and alkali metal trapping sites. The HMT@Cu–S catalysts exhibited excellent SCR activity and N2 selectivity. More importantly, the HMT@Cu–S catalysts had stronger resistance against alkali metal poisoning compared to Cu-SAPO-34 catalysts. It was found that these newly developed catalysts had superior alkali metal resistance compared to the reported catalysts, making them attractive for environmental application. The hollandite Mn–Ti oxides acted as a protective layer to trap alkali metal ions according to an ion exchange mechanism. From in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) studies of desorption, it could be concluded that after alkali metal poisoning, the NH3 species of the HMT@Cu–S catalysts were more unstable; therefore, they could easily participate in the SCR reactions. Additionally, the NOx species showed no change after introduction of alkali metal ions due to alkali metal trapping effects. Moreover, the in situ DRIFTS of transient reactions indicated that the NH3 species were much more easily adsorbed on K-HMT@Cu–S catalysts and that the formed NH3 species that were unaffected by alkali metal ions were highly reactive. The present investigations provide an effective strategy for the design and the application of catalysts with outstanding catalytic activity and alkali metal resistance.

77 citations

Journal ArticleDOI
TL;DR: In this article, high active nanoparticle SCR deNOX catalysts composed of amorphous vanadia on crystalline anatase have been prepared by a sol-gel, co-precipitation method using decomposable crystallization seeds.

77 citations

Journal ArticleDOI
TL;DR: In this article, a gas-phase FT-IR analyzer was used for the first time to spatially resolve gas concentrations in a monolith-supported SCR catalyst, including standard SCR, fast SCR and SCR with NO2.
Abstract: There have been several recent reports regarding the spatial resolution of gas species in monolith-supported automobile exhaust catalysts, with examples including characterization of DOCs (diesel oxidation catalysts) and LNTs (lean NOx traps). However, spatially resolving gas concentrations in NH3-SCR (selective catalytic reduction) applications is limited due to the difficulty in ppm-level NH3 detection in the presence of percent levels of water and N2 using mass spectrometry. In this study, a gas-phase FT-IR analyzer was used for the first time to spatially resolve gas concentrations in a monolith-supported SCR catalyst. The reactions analyzed include standard SCR, fast SCR and SCR with NO2. The results show that the three SCR reactions proceed at significantly different rates, especially at temperatures below 300 °C, and can be correlated to the amount of catalyst used. For example, the catalyst lengths needed to achieve 80% NOx conversion at 300 °C are 2.4, 1.2 and 0.5 cm for conditions that meet the standard SCR, NO2-SCR and fast SCR reaction stoichiometries, respectively. For the standard SCR reaction, kinetic analysis, and spatially resolved NO oxidation and SCR results consistently indicate that the rate-determining step is NO oxidation. NH3 has an inhibition effect, as it suppresses NO oxidation by competitive adsorption on the active sites. At 300 °C, the outlet NOx conversion is not limited by the reaction kinetics, but by insufficient NH3 supply, since part of the NH3 is oxidized by O2. Compared with 300 °C, higher NOx conversions are attained at 400 or 500 °C, which is due to significantly enhanced NO oxidation, and the resulting increase in NH3 reacting with NOx via SCR rather than O2 via NH3 oxidation. For NO2-SCR, a considerable amount of N2O was formed at 250 °C but decreased with increasing temperature. The decreased N2O is due to improved selectivity in the NO2-SCR to N2, as well as N2O decomposition at the back part of the catalyst at high temperature. Finally, different SCR reaction patterns were identified when testing with NO:NO2 = 3:1 and 1:3. For NO:NO2 = 3:1, the SCR reactions proceed in series, namely through the fast reaction first, followed by standard SCR. The fast SCR and NO2-SCR reactions proceed in parallel for NO:NO2 = 1:3. The results indicate that if NO2 is the limiting reactant, fast SCR dominates, but if excess NO2 is available, the NO2 SCR reaction can proceed in parallel.

77 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023311
2022632
2021546
2020583
2019604
2018595