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.

Effect of CuMn2O4 spinel in Cu-Mn oxide catalysts on selective catalytic reduction of NOx with NH3 at low temperature

Abstract: Using the impregnation method, a series of Cu–Mn oxide catalysts were prepared and investigated for the selective catalytic reduction (SCR) of NOx with NH3 at temperatures ranging from 353 K to 453 K. The 0.05Cu–MnOx/TiO2 catalyst shows the highest activity and yields nearly 100% NOx conversion at 453 K using GHSV = 40 000 h−1, while the 0.20Cu–MnOx/TiO2 catalyst exhibits a certain level of potassium tolerance. In addition, the catalysts show favorable stability and water resistance. According to the XRD, EDS and SCR performance results, the existence of a new crystallized CuMn2O4 spinel phase is the dominant parameter for outstanding SCR activity between 413 K and 453 K. TPR, XPS and in situ DRIFT experiments indicate that CuMn2O4 is responsible for low reduction temperature, strong interaction between manganese oxides and copper oxides, high Mn3+ content and numerous acid sites on the surface. Compared with MnOx/TiO2 catalysts, Cu–Mn oxide catalysts could reduce the poisoning effect of potassium, illustrating that the CuMn2O4 phase may play a significant role in K-tolerance. Meanwhile, based on a certain level of potassium tolerance in CuMn2O4, an oxidation mechanism for NO is proposed due to the increase in Mn3+ and the special structure of a spinel oxide.

Stability and activity of Pd-, Pt- and Pd–Pt catalysts supported on alumina for NO oxidation

Abstract: The association of palladium and platinum supported on alumina was studied for diesel oxidation catalyst application. The effect of propene, water and their combination on NO oxidation activity was investigated in flow reactor over Pt/Al2O3, Pd/Al2O3 and two Pt-Pd/Al2O3 catalysts, prepared by co-impregnation and sequential impregnation of the metals. Contrary to Pd/Al2O3, activity improvement due to the repetition of activity test was observed on Pt/Al2O3 and both Pt-Pd/Al2O3. Metal sintering during activity test was revealed by CO chemisorption. The bimetallic catalysts reached their final stability and activity before Pt/Al2O3. The presence of water decreased the NO oxidation activity of all catalysts and the propene completely inhibited NO oxidation at low temperature until propene combustion occurred. The addition of palladium to Pt/Al2O3 was found very efficient to oxidize propene and therefore significantly limited the inhibition of NO oxidation by propene. A mechanism was proposed to explain the NO oxidation promotion lying behind the addition of Pd. DRIFT measurements and flow reactor experiments showed that propene was less stable and able to react with surface nitrates on Pd-containing catalyst at low temperature (175 degrees C). On Pt/Al2O3, however, the propene consumption proceeded initially through selective catalytic reduction of NO, which took place at higher temperature (240 degrees C). In this way, propene combustion and consequently NO oxidation occurred at lower temperature on bimetallic catalysts than on Pt/Al2O3.

Novel V 2 O 5 -CeO 2 -TiO 2 -SO 4 2− nanostructured aerogel catalyst for the low temperature selective catalytic reduction of NO by NH 3 in excess O 2

Abstract: New ceria and sulfate co-modified V2O5-TiO2 aerogel catalysts were developed, using the one-step sol gel method associated with the supercritical drying process, for Diesel DeNOx technology. N2 adsorption-desorption, XRD, H2-TPR, NH3-TPD, Raman and DRUV-Vis spectroscopy were employed to probe the physico-chemical properties of TiO2, V2O5-TiO2, V2O5-CeO2-TiO2 and V2O5-CeO2-TiO2-SO42− aerogel materials. XPS was used to obtain further information about the oxidation states of the active sites on the surface of the novel V2O5-CeO2-TiO2-SO42− aerogel catalyst. The characterization results showed the successful synthesis of a new generation of well nanostructured aerogel catalysts with high surface area, large porosity and good thermal stability. V, Ce and SO42− actives species were found highly dispersed on TiO2 surface and their presence strongly influenced the surface acidity and the redox properties of the aerogel catalysts. Sulfate anions created strong acid sites and most probably contributed to the stabilization of V and Ce surface species at their 4 + and 3 + oxidation state, respectively. In the SCR-NO by NH3 under oxygen rich conditions, V2O5-TiO2 aerogel catalyst exhibited low NO conversions in 150–500 °C temperature range. The addition of cerium significantly increased the NO conversion at low temperature (220–400 °C). However, the simultaneous incorporation of cerium and sulfate has led to a novel V2O5-CeO2-TiO2-SO42− nanostructured aerogel catalyst with superior catalytic performances, at high temperature (450–500 °C), with respect to V2O5-WO3/TiO2 commercial one (EUROCAT).

Catalytic reduction of NH4NO3 by NO: Effects of solid acids and implications for low temperature DeNOx processes

Abstract: Ammonium nitrate is thermally stable below 250 °C and could potentially deactivate low temperature NO x reduction catalysts by blocking active sites It is shown that NO reduces neat NH 4 NO 3 above its 170 °C melting point, while acidic solids catalyze this reaction even at temperatures below 100 °C NO 2 , a product of the reduction, can dimerize and then dissociate in molten NH 4 NO 3 to NO + + NO 3 − , and may be stabilized within the melt as either an adduct or as HNO 2 formed from the hydrolysis of NO + or N 2 O 4 The other product of reduction, NH 4 NO 2 , readily decomposes at ≤100 °C to N 2 and H 2 O, the desired end products of DeNO x catalysis A mechanism for the acid catalyzed reduction of NH 4 NO 3 by NO is proposed, with HNO 3 as an intermediate These findings indicate that the use of acidic catalysts or promoters in DeNO x systems could help mitigate catalyst deactivation at low operating temperatures (