Catalyst For Selective Catalytic Reduction Of NOx Research Articles

Experimental and DFT study of the adsorption and activation of NH3 and NO on Mn-based spinels supported on TiO2 catalysts for SCR of NOx

CuMn2O4 and NiMn2O4 spinels supported on TiO2 were prepared by the impregnation method, and their efficiencies of selective catalytic reduction (SCR) of NOx with NH3 in the simulated flue gas were researched. The two kinds of catalysts showed high NH3-SCR activity for NOx removal over a range of temperature (353–453 K). According to the in situ diffuse reflectance infrared transform spectroscopy (in situ DRIFTS) test, a larger quantity of adsorbed NH3 was detected for CuMn2O4 when NH3 was introduced, and NiMn2O4 provided a larger adsorption amount of NO when NO was introduced. Meanwhile, the corresponding slab models were constructed by density functional theory (DFT) calculations to investigate the adsorption of NH3 and NO molecules. The DFT calculations of NO adsorption were in agreement with the results that were observed by the experiments.

Direct synthesis of submicron Cu-SAPO-34 as highly efficient and robust catalyst for selective catalytic reduction of NO by NH3

High-performance and ultra-stable selective catalytic reduction (SCR) catalyst with low-cost is needed for controlling NOx emissions of the Euro 6 diesel vehicle. The combination of copper-tetraethylenepentamine (Cu-TEPA) and morpholine (MOR) as templates allowed the direct synthesis of highly active and hydrothermally stable submicron Cu-SAPO-34 catalyst for SCR of NOx with NH3 (NH3-SCR). It exhibited much better catalytic activity and hydrothermal stability than the reference catalyst synthesized with Cu-TEPA, diethylamine and tetraethylammonium bromide as templates. The origin of superior SCR performance of the submicron Cu-SAPO-34 catalyst was investigated by a series of characterization techniques including XRD, N2 sorption, NMR, NH3-TPD, H2-TPR, UV–vis-DRS and XPS. Consequently, the structure-performance relationship of the submicron Cu-SAPO-34 catalyst was well established. The isolated Cu2+ ions exist predominantly in submicron Cu-SAPO-34 with a plenty of Si (nOAl) (n = 1–4) structures. These Si coordination structures could generate a large number of Brønsted acid sites, which could be beneficial for NO reduction. The typical cubic crystal and isolated Cu2+ ions remain stable even after steaming at 800 °C for 12 h. Furthermore, the amount of isolated Cu2+ ions increase and copper oxides decrease and redistribute after steaming. The NH3-SCR kinetic test further proved the superior NH3-SCR performance of the submicron Cu-SAPO-34 catalyst.

Sulfur and Water Resistance of Mn-Based Catalysts for Low-Temperature Selective Catalytic Reduction of NOx: A Review

Selective catalytic reduction (SCR) with NH3 is the most efficient and economic flue gas denitrification technology developed to date. Due to its high low-temperature catalytic activity, Mn-based catalysts present a great prospect for application in SCR de-NOx at low temperatures. However, overcoming the poor resistance of Mn-based catalysts to H2O and SO2 poison is still a challenge. This paper reviews the recent progress on the H2O and SO2 resistance of Mn-based catalysts for the low-temperature SCR of NOx. Firstly, the poison mechanisms of H2O and SO2 are introduced in detail, respectively. Secondly, Mn-based catalysts are divided into three categories—single MnOx catalysts, Mn-based multi-metal oxide catalysts, and Mn-based supported catalysts—to review the research progress of Mn-based catalysts for H2O and SO2 resistance. Thirdly, several strategies to reduce the poisonous effects of H2O and SO2, such as metal modification, proper support, the combination of metal modification and support, the rational design of structure and morphology, are summarized. Finally, perspectives and future directions of Mn-based catalysts for the low-temperature SCR of NOx are proposed.

Low temperature selective catalytic reduction of NO<sub>x</sub> with NH<sub>3</sub> over Mn-based catalyst: A review

The removals of NOx by catalytic technology at low temperatures (100–300 °C) for industrial flue gas treatment have received increasing attention. However, the development of low temperature catalysts for selective catalytic reduction (SCR) of NOx with ammonia is still a challenge especially in the presence of SO2. The current status of using Mn-based catalysts for low temperature SCR of NOx with ammonia (NH3-SCR) is reviewed. Reaction mechanisms and effects of operating factors on low temperature NH3-SCR are addressed, and the SCR efficiencies of Mn-based metal oxides with and without SO2 poisoning have also been discussed with different supports and co-metals. The key factors for enhancing low temperature NH3-SCR efficiency and SO2 resistance with Mn-based catalysts are identified to be (1) high specific surface area; (2) high surface acidity; (3) oxidation states of manganese; (4) well dispersion of manganese oxide metals; (5) more surface adsorbed oxygen; (6) more absorbed NO3− on the catalyst surface; (7) easier decomposition of ammonium sulfates. Moreover, the regenerative methods such as water washing, acid and/or alkali washing and heat treatment to the poisoned catalysts could help to recover the low temperature SCR efficiency to its initial level.

Influence of elevated surface texture hydrated titania on Ce-doped Mn/TiO2 catalysts for the low-temperature SCR of NOx under oxygen-rich conditions

In order to boost the low-temperature activity, a series of Mn–Ce/TiO2-X (X=Hk, N1, N2 and N3) were prepared by adopting incipient wetness technique and investigated for the low-temperature selective catalytic reduction (SCR) of NOx with NH3 at industrial relevant conditions. Prior to that, hydrous TiO2-nanosized samples were synthesized by a deposition technique at constant pH kept in the range of 5–8 and constant temperature 30–80°C. Titanium oxide hydrates (N1, N2, and N3) possess high specific surface area as 620m2/g, 457m2/g, 398m2/g, whereas TiO2 (Hk) preserves 309m2/g surface area. In our studies, it was found that the NOx conversion over Mn–Ce/TiO2-Hk with the atomic ratio of Mn/Ce=5.1 was apparently higher compared with that over Mn–Ce(5.1)/TiO2-X (X=N1, N2, and N3). Our activity results showed that 93.0% NOx conversion was obtained over Mn–Ce(5.1)/TiO2-Hk at 100°C at a space velocity of 80,000h−1. Our XRD results suggest that the loading of manganese and ceria onto hydrated titania led to the evolution of diffraction peaks which can be attributed to the formation of crystalline manganese dioxide (MnO2). Among all the catalysts, Mn–Ce/TiO2 N2 showed high intensity diffraction peaks at 2θ=37.2°, which corresponds to the highly crystalline (101) plane of manganese dioxide. Once the catalysts with the best performance were identified, experiments were performed with the aim of optimizing these formulations with respect to the dopant and Mn/Ce atomic ratio. Both the ceria co-doping and Mn/Ce atomic ratios played a key role to achieve high NOx conversions at 100°C. The disappearance or low-temperature shift of ceria reduction peak in H2-TPR indicates the increase of active components’ reduction potential, oxygen vacancies, and the existence of surface-capping oxygen species in Mn–Ce/TiO2 (Hk). The H2-TPR results are in good accordance with our XPS analysis where the relative atomic ratios of Mn4+/Mn3+, Ce3+/Ce4+, and the existence of surface oxygen species greatly enhanced in Mn–Ce/TiO2 (Hk) compared to other catalysts in this work. The relative atomic ratio of Mn4+/Mn3+ (2.19) in Mn–Ce(5.1)/TiO2-Hk calculated from deconvoluted XPS spectra is much higher than that of other catalysts (1.90, 0.89, and 2.03 for N1, N2, and N3, respectively). Moreover, the superior ratio of Ce3+/Ce4+ can generate a charge imbalance, oxygen vacancies, and unsaturated chemical bonds over the catalyst surface to promote the oxidation of NO to NO2. It is highly remarkable to note that the deNOx efficiency of all the prepared catalysts is indeed correlated with the surface concentrations of Ce3+/Ce4+ and Mn4+/Mn3+. NH3-TPD results imply that the co-doping of manganese and ceria onto Hk TiO2 can remarkably improve the acid sites distribution and the concentration of acid sites of the Mn–Ce/TiO2 catalyst. Our investigation results illustrate that the enhancement in reduction potential of active components, broadening of acid sites distribution, and the promotion of Mn4+/Mn3+, Ce3+/Ce4+ ratios including surface labile oxygen and small pore openings seem to be the reason for high deNOx efficiency of Mn–Ce/TiO2 (Hk) at low temperatures.

Mass transport and kinetics in structured steel foam reactor with Cu-ZSM-5 catalyst for SCR of NOx with ammonia

Continued research on improving heat and mass transfer properties of structured catalysts is essential for the development of an effective catalytic system. In this paper, the transfer parameters (mass and heat) and pressure drop across reactors prepared with metal foams of different materials (FeCrAl and Al) and PPI (pores per inch) are presented. The mass transfer parameter was determined by correlation using the Chilton–Colburn analogy, and the heat transfer and pressure drop parameters were determined experimentally.Additionally the kinetic properties of a short channel reactor structure based on metallic foams and template-less synthesized ZSM-5 were determined for the selective catalytic reduction (SCR) of NO with ammonia and compared to commonly used commercial solutions – i.e. packed bed and honeycomb monolith reactor structures.

Preparation and Performance of Several Non-Precious Metal Oxides Catalysts for the Low Temperature SCR of NOx with NH<sub>3</sub>

A series of non-precious metal oxides catalysts were prepared for low-temperature selective catalytic reduction (SCR) of NOx with NH3 in a fixed bed reactor. The catalytic performance was evaluated by the removal efficiency of NOx and N2 selectivity which were respectively detected by flue gas analyzer and flue gas chromatograph. Furthermore, the components of gas products from the above experiments were analysed with 2010 GC-MS. The results illustrated that the MnO2 exhibited the highest NOx conversion to 95.46% and the highest selectivity of N2 to 100% at temperature of 393K, then followed ZrO2, Al2O3 and Fe2O3.