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.

Characterization of Nb-Containing MnOx−CeO2 Catalyst for Low-Temperature Selective Catalytic Reduction of NO with NH3

Abstract: The reactivity in the selective catalytic reduction of the individual and binary components of NbOx−MnOx−CeO2 catalysts has been studied with coated cordierite monoliths in the temperature range of 150−450 °C. FTIRS, DRIFTS, TA, XRD, BET, and XAS have been used to elucidate the structural and catalytic properties. The results confirmed the contribution of the manganese oxides, particularly to the low-temperature NO-to-NO2 oxidation reaction. The significant increase of the surface acidity as a result of niobium oxide addition has been established. The data obtained revealed also the strong interaction between the manganese and niobium catalytic active sites. This phenomenon leads to a very good distribution of the oxidizing and acidic sites in the catalyst structure and also diminishes the unselective NH3 oxidation at higher temperatures. However, in order to keep the low-temperature catalytic activity, an excess of manganese relative to the niobium content is needed.

Kinetics of selective catalytic reduction of NO with NH3 on Fe-ZSM-5 catalyst

Abstract: Fe-exchanged ZSM-5 has been found previously to be much more active than commercial vanadia-based catalysts for selective catalytic reduction (SCR) of NO with NH3. The kinetics of the SCR reaction is studied in this work. The results show that the rate of NO conversion on Fe-ZSM-5 is first-order with respect to NO, zeroth-order w.r.t. NH3 and nearly half-order w.r.t. O2, at 260–300 °C. This is in good agreement with our previous FTIR result that the catalyst surface is nearly completely covered by ammonia adsorbed species (i.e. NH4+ ions) under reaction conditions. The present results further support that the SCR mechanism on Fe-ZSM-5 involves NO2 as an intermediate and the formation of NO2 from NO oxidation (NO+(1/2)O2→NO2) is probably the rate-determining step. The apparent activation energy for the reaction is found to be 54 kJ/mol.

Promoted V2O5/TiO2 catalysts for selective catalytic reduction of NO with NH3 at low temperatures

Abstract: The influence of varying the V2O5 content (3–6 wt.%) was studied for the selective catalytic reduction (SCR) of nitrogen oxides by ammonia on heteropoly acid (HPA)- and tungsten oxide (WO3)-promoted V2O5/TiO2 catalysts. The SCR activity and alkali deactivation resistance of HPA-promoted V2O5/TiO2 catalysts was found to be much higher than for WO3- promoted catalysts. By increasing the vanadium content from 3 to 5 wt.% the catalysts displayed a two fold increase in activity at 225 °C and retained their initial activity after alkali doping at a molar K/V ratio of 0.181. Furthermore, the catalysts were characterized by N2 physisorption, XRPD, NH3-TPD, H2-TPR, Raman, FTIR and EPR spectroscopy to investigate the properties of the catalysts. XRPD, Raman and FTIR showed that promotion with 15 wt.% HPA does not cause V2O5 to be present in crystalline form, also at a loading of 5 wt.% V2O5. Hence, use of HPAs does not cause increased N2O formation or unselective oxidation of NH3. NH3-TPD showed that promotion by HPA instead of WO3 causes the catalysts to possess a higher number of acid sites, both in fresh and alkali poisoned form, which might explain their higher potassium tolerance. Ex-situ EPR spectroscopy revealed that HPA-promoted catalysts have higher V4+/Vtotal ratios than their WO3-promoted counterparts. H2-TPR suggests that HPAs do not have a beneficial effect on the V5+-V3+ redox system, relative to WO3.

Oxidation of mercury across selective catalytic reduction catalysts in coal-fired power plants.

Abstract: A kinetic model for predicting the amount of mercury (Hg) oxidation across selective catalytic reduction (SCR) systems in coal–fired power plants was developed and tested. The model incorporated the effects of diffusion within the porous SCR catalyst and the competition between ammonia and Hg for active sites on the catalyst. Laboratory data on Hg oxidation in simulated flue gas and slipstream data on Hg oxidation in flue gas from power plants were modeled. The model provided good fits to the data for eight different catalysts, both plate and monolith, across a temperature range of 280–420 °C, with space velocities varying from 1900 to 5000 hr–1. Space velocity, temperature, hydrochloric acid content of the flue gas, ratio of ammonia to nitric oxide, and catalyst design all affected Hg oxidation across the SCR catalyst. The model can be used to predict the impact of coal properties, catalyst design, and operating conditions on Hg oxidation across SCRs.