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.

SCR on low thermal mass filter substrates

Abstract: Provided are selective catalytic reduction (SCR) filters that effectively provide simultaneous treatment of particulate matter and NOx. Provided also are methods for reducing NOx concentration and particulate matter in a diesel engine exhaust by using the SCR filters. The SCR filter can include a fiber matrix wall flow filter comprising a plurality of non-woven inorganic fibers and a chabazite molecular sieve SCR catalyst on the fiber matrix wall flow filter. By combining a fiber matrix wall flow filter with a chabazite molecular sieve SCR catalyst, high catalyst loading can be achieved without causing excessive back pressure across the filter when implemented in emission treatment systems.

Inhibiting and deactivating effects of water on the selective catalytic reduction of Nitric Oxide with ammonia over MnOx/Al2O3

Abstract: The effect of water on the selective catalytic reduction (SCR) of nitric oxide with ammonia over alumina supported with 2–15 wt.-% manganese oxide was investigated in the temperature range 385–600 K, with the emphasis on the low side of this temperature window. Studies on the effect of 1–5 vol.-% water vapour on the SCR reaction rate and selectivity were combined with TPD experiments to reveal the influence of water on the adsorption of the single SCR reactants. It turned out that the activity decrease due to water addition can be divided into a reversible inhibition and an irreversible deactivation. Inhibition is caused by molecular adsorption of water. TPD studies showed that water can adsorb competitively with both ammonia and nitric oxide. Additional kinetic experiments revealed that adsorbed ammonia is present in excess on the catalyst surface, even in the presence of water. Reduced nitric oxide adsorption is responsible for the observed reversible decrease in the reaction rate; the fractional reaction order changes from 0.79 in the absence of water to 1.07 in its presence. Deactivation is probably due to the dissociative adsorption of water, resulting in the formation of additional surface hydroxyls. As the amount of surface hydroxyls formed is limited to a saturation level, the deactivating effect on the catalyst is limited too. The additional hydroxyls condense and desorb in the temperature range 525–775 K, resulting in a lower degree of deactivation at higher temperature. A high temperature treatment at 775 K results in a complete regeneration. The amount of surface hydroxyls formed per unit surface area decreases at increasing MnOx-loading. The selectivity to the production of nitrogen is enhanced significantly by the presence of gas phase water.

NH3-SCR Performance of Fresh and Hydrothermally Aged Fe-ZSM-5 in Standard and Fast Selective Catalytic Reduction Reactions

Abstract: Hydrothermal stability is one of the challenges for the practical application of Fe-ZSM-5 catalysts in the selective catalytic reduction (SCR) of NO with NH3 (NH3-SCR) for diesel engines. The presence of NO2 in the exhaust gases can enhance the deNOx activity because of the fast SCR reaction. In this work, a Fe- ZSM-5 catalyst was prepared by a solid-state ion-exchange method and was hydrothermally deactivated at 800 °C in the presence of 10% H2O. The activity of fresh and hydrothermal aged Fe-ZSM-5 catalysts was investigated in standard SCR (NO2/NOx = 0) and in fast SCR with NO2/NOx = 0.3 and 0.5. In standard SCR, hydrothermal aging of Fe-ZSM-5 resulted in a significant decrease of low-temperature activity and a slight increase in high- temperature activity. In fast SCR, NOx conversion over aged Fe- ZSM-5 was significantly increased but was still lower than that over fresh catalyst. Additionally, production of N2O in fast SCR was much more apparent over aged Fe-ZSM-5 than over fresh catalyst. We propose that, in fast SCR, the rate of key reactions related to NO is slower over aged Fe-ZSM-5 than over fresh catalyst, thus increasing the probabilities of side reactions involving the formation of N2O.

Alkali deactivation of high-dust SCR catalysts used for NOx reduction exposed to flue gas from 100 MW-scale biofuel and peat fired boilers: Influence of flue gas composition

Abstract: Deactivation of vanadium–titanium deNO x SCR (selective catalytic reduction) catalysts in high-dust position have been investigated in three 100 MW-scale boilers during biofuel and peat combustion. The deactivation of the catalyst samples has been correlated to the corresponding flue gas composition in the boilers. Too investigate the effect on catalyst deactivation a sulphate-containing additive was sprayed into one of the furnaces. Increased alkali content on the SCR catalyst samples decreased the catalytic deNO x activity. The study has shown a linear correlation between exposure time in the boilers and alkali concentration (mainly potassium) on the samples. The results imply that mainly alkali in ultra fine particles (

Process and device for selective catalytic NOx reduction in exhaust gases containing oxygen

Abstract: For the operation of an SCR catalyst (5) for nitrogen oxide reduction, it is proposed to spray urea solution finely from a container (8) onto a heated vaporiser/catalyst (3) and, if necessary, to carry out an aftertreatment by means of a downstream hydrolysis catalyst (4). The result is that the reduction catalyst is subjected only to the ammonia eliminated from the urea and to the waste gas (12) to be purified, and the formation of other pollutants and contamination of the catalyst are thus avoided.