Selective Catalytic Reduction Activity Research Articles

Investigating cylinder deactivation as a low fuel-penalty thermal management strategy for heavy-duty diesel engines

The upcoming ultra-low-NOx (oxides of nitrogen) emissions standard and in-use NOx emissions requirement requires engine manufacturers to further reduce tailpipe NOx emissions by over 90% from the current United States Environmental Protection Agency 2010 heavy-duty emissions standard. To meet ultra-low NOx standards, significant improvements to the NOx reduction capability of the Selective Catalytic Reduction (SCR) system is required. Low-temperature exhaust conditions and the associated fuel penalty in increasing the exhaust temperatures for improving catalyst activity is an engineering challenge to balance lowering NOx emissions while lowering fuel consumption. Cylinder Deactivation (CDA) in diesel engines has shown the ability to increase exhaust temperatures while maintaining a zero-fuel penalty. This study details the results of the performance of a CDA hardware installed in a modern heavy-duty diesel engine. The study was aimed at developing steady-state engine calibrations to maximize exhaust temperatures while realizing a zero-fuel penalty or improved BTE operation during low-load engine operating conditions for an on-road heavy-duty diesel engine. In addition, the study demonstrated the effect of CDA on lowering aftertreatment cooldown during motoring operation. The results of the study showed close to a 100°C increase in turbine out temperatures (TOT) at idle, 1,000 rpm and 1,200 rpm engine speeds with engine load at 10 and 20% of rated torque. The results also showed that deactivating three of the six cylinders during motoring operation of the low-load cycle delayed after treatment cool down and maintained exhaust temperatures above the SCR activity threshold for a longer duration.

Effects of Nb-modified CeVO4 to form surface Ce-O-Nb bonds on improving low-temperature NH3-SCR deNOx activity and resistance to SO2 & H2O

A series of novel ternary CeVO4 modified with different Nb contents (CeNbVO) catalysts were synthesized via alkali-assisted hydrothermal method, and applied for selective catalytic reduction (SCR) of NOx with NH3. The as-prepared CeNbVO catalysts show enhanced NH3-SCR performance compared with the CeVO catalyst. Especially, the optimal CeNbVO-2 with appropriate Nb amount displays the superior NH3-SCR activity with above 90 % NO conversion in the range of 210–420 °C with 5 %vol·H2O and excellent resistance to H2O/SO2. Effects of Nb-modified CeVO4 to form surface Ce-O-Nb bonds on improving low-temperature NH3-SCR activity and resistance to SO2 & H2O were investigated by using various characterization methods, including XRD, Raman spectroscopy, N2 physical adsorption, TEM, H2-TPR, NH3-TPD, O2-TPD, NO-TPD, XPS, kinetic tests and in-situ DRIFTS. Different phases can be obtained with the different Nb amount doping, leading to different SCR activity. The pure CeVO4 phase with the short-range ordered Nbn+–O2–-Cen+ bond is formed by adding a small amount of Nb in CeNbVO-2. The superior catalytic performance of CeNbVO-2 can be ascribed to its improved acidity and suitable oxidation ability, which may counteract the negative effects of nonselective NH3 oxidation to N2O. It is found that the formation of Nbn+–O2–-Cen+ bonds can significantly increase the surface active oxygen species and oxygen vacancy of the catalyst. Additionally, the NH3-SCR reaction mechanism is revealed using in-situ DRIFTS and kinetic studies.

CeO2 Nanoparticle-Loaded MnO2 Nanoflowers for Selective Catalytic Reduction of NOx with NH3 at Low Temperatures.

CeO2 nanoparticle-loaded MnO2 nanoflowers, prepared by a hydrothermal method followed by an adsorption-calcination technique, were utilized for selective catalytic reduction (SCR) of NOx with NH3 at low temperatures. The effects of Ce/Mn ratio and thermal calcination temperature on the NH3–SCR activity of the CeO2-MnO2 nanocomposites were studied comprehensively. The as-prepared CeO2-MnO2 catalysts show high NOx reduction efficiency in the temperature range of 150–300 °C, with a complete NOx conversion at 200 °C for the optimal sample. The excellent NH3–SCR performance could be ascribed to high surface area, intimate contact, and strong synergistic interaction between CeO2 nanoparticles and MnO2 nanoflowers of the well-designed composite catalyst. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs) characterizations evidence that the SCR reaction on the surface of the CeO2-MnO2 nanocomposites mainly follows the Langmuir–Hinshelwood (L-H) mechanism. Our work provides useful guidance for the development of composite oxide-based low temperature NH3–SCR catalysts.

Investigation of RuOx doping stimulated the high catalytic activity of CeOx-MnOx/TiO2 catalysts in the NH3-SCR reaction: Structure-activity relationship and reaction mechanism

CeO x -MnO x /TiO 2 (CMT) is the prototype, low-temperature (150–250 ℃) mixed oxide NH 3 -deNO x catalyst with the greatest potential for industrial application. The improvement of ultra-low temperature (60–150 ℃) denitration activity, SO 2 and alkali resistance of CMT catalysts received significant attention. RuO x has been widely utilized in selective catalytic oxidation (SCO), and we believe that the catalyst must first undergo SCO before selective catalytic reduction (SCR). Therefore, a series of RuO x -CMT catalysts were prepared by impregnating RuO x with CMT as the carrier and their catalytic mechanism at low temperature and activity analyzed in detail through XRF, XRD, BET, TEM, HRTEM, STEM+EDS, XPS, H 2 -TPR, NH 3 -TPD-MS and in situ DRIFTS characterizations. The obtained results show that RuO x modification significantly improved the low-temperature denitrification activity of CMT by enhancing the interaction of Ce, Mn and Ti, promoting the conversion of inactive bidentate nitrate to the active monodentate nitrate and strengthening the Mars-van Krevelen (M-K), Langmuir-Hinshelwood (L-H), and Eley-Rideal (E-R) mechanisms. • RuO x doping stimulates the high NH 3 -SCR activity of CeO x -MnO x /TiO 2 catalysts. • RuO x modification significantly promotes the dispersion of Ce, Mn, and Ti elements. • Addition of RuO x strengthens the M-K, L-H and E-R mechanisms at low temperature. • RuO x converts inactive bidentate nitrate into active monodentate nitrate. • Monodentate nitrate is the main NO activation species reacting with NH x species.

One‐pot facile synthesis of Cu‐SAPO‐34 via addition of tetraethylenepentamine and its enhanced catalytic activity in selective catalytic reduction of NOx with NH3

AbstractBACKGROUNDA series of Cu‐SAPO‐34 samples were prepared with different copper sources and addition of tetraethylenepentamine (TEPA) by a one‐pot method, which were applied for selective catalytic reduction of NOx with ammonia (NH3‐SCR).RESULTSVarious measurements were carried out to investigate the effect of TEPA addition and copper sources used on sample properties. The results indicated that Cu‐SAPO‐34 obtained with the addition of TEPA using copper citrate (Cu‐SAPO‐34‐TC) displayed over 90% NOx conversion at 150–500 °C and excellent H2O and SO2 resistance in NH3‐SCR. This is because the addition of TEPA can control the formation of isolated Cu2+ species located at the junction of D6R in CHA cage, Site (I), which is regarded as a more easily approachable site to adsorbates (NH3 and NO) than others, thus leading to the excellent NH3‐SCR performance. Further study demonstrated that the Cu‐SAPO‐34‐TC catalyst shows much wider temperature window and more hydrothermal stability due to a greater amount of surface isolated Cu2+, fewer Si islands and more Al(IV) species.CONCLUSIONSThe excellent activity of the Cu‐SAPO‐34‐TC catalyst can be attributed to the addition of TEPA, which is beneficial for controlling the isolated Cu2+ at Site (I) as well as inhibiting the aggregation of CuO species. Various characterizations also confirm that more surface Cu2+ can be produced using copper citrate as copper source. © 2022 Society of Chemical Industry (SCI).

Ordered Mesoporous MnAlOx Oxides Dominated by Calcination Temperature for the Selective Catalytic Reduction of NOx with NH3 at Low Temperature

Manganese alumina composited oxides (MnAlOx) catalysts with ordered mesoporous structure prepared by evaporation-induced self-assembly (EISA) method was designed for the selective catalytic reduction (SCR) of NOx with NH3 at low temperature. The effect of calcination temperature of MnAlOx catalysts was investigated systematically, and it was correlated with SCR activity. Results showed that with an increase in calcination temperature, the SCR activity of MnAlOx catalysts increased. When the calcination temperature was raised up to 800 °C, the NOx conversion was more than 90% in the operation temperature range of 150~240 °C. Through various characterization analysis, it was found that MnAlOx-800 °C catalysts possessed enhanced redox capacities as the higher content of Mn4+/(Mn3+ + Mn4+). Moreover, the improved redox properties could contribute to a higher NOx adsorption and activation ability, which lead to higher SCR performance of MnAlOx-800 °C catalysts. In situ DRIFTs revealed that the adsorbed NO2 and bidentate nitrate are the reactive intermediate species, and NH3 species bonded to Lewis acid sites taken part in SCR progress. The SCR progress predominantly followed E–R mechanism, while L–H mechanism also takes effect to a certain degree.

Low-temperature NOx selective catalytic reduction activity evaluation of hollow-spherical manganese oxides

Low-temperature NOx selective catalytic reduction activity evaluation of hollow-spherical manganese oxides

Effect of acidic components (SO42- and WO3) on the surface acidity, redox ability and NH3-SCR activity of new CeO2-TiO2 nanoporous aerogel catalysts: A comparative study

• New CeTiSO 4 2- and WO 3 -CeTi nanoporous aerogel catalysts for NH 3 -SCR reaction. • SO 4 2- modifies the nature of Ce species and increases the acidity of the CeTi aerogel. • WO 3 generates more reactive surface oxygen and active redox sites at CeTi surface. • WO 3 -CeTi displays the highest SCR activity at 320–400 °C (NO conversion > 90 %) • CeTiSO 4 2- exhibits superior SCR performance at 450–500 °C (NO conversion > 90 %) Selective catalytic reduction (SCR) of nitrogen oxide (NO) by ammonia (NH 3 ) was studied in this work over new sulfate (SO 4 2- ) or tungsta (WO 3 ) modified CeO 2 -TiO 2 aerogel catalysts. The catalytic systems were elaborated via sol gel method then characterized by: XRD, N 2 -Physisorption at 77 K, DRUV–vis, NH 3 -TPD and H 2 -TPR. It was revealed that the nature of acidic components influences differently the texture, surface oxygen concentration, acidity, reducibility and NH 3 -SCR activity of new Ce-based catalysts. Hence, the incorporation of sulfate modifies the nature of Ce species, improves their dispersion through the Ce-SO 4 2- interactions and, particularly, generates new strong acid sites which display superior catalytic performance at high temperature NO reduction (NO conversion into N 2 > 90 % between 450 and 500 °C over CeO 2 -TiO 2 -SO 4 2- catalyst). However, the addition of tungsta affects slightly the surface acidity of CeO 2 -TiO 2 catalyst but it induces the creation of more reactive surface oxygen and new redox sites at its surface (mainly due to the existence of W-Ce interactions) leading to highly active WO 3 -CeO 2 -TiO 2 system for the low temperature NH 3 -SCR reaction with above 90 % NO conversion into N 2 between 320 and 400 °C.

Thulium oxides supported on MnCeTiOX catalysts for low-temperature NH3-SCR of NOX

In this work, the MnCeTiOX catalyst was prepared by sol-gel method and doped with thulium (Tm), which improved its low-temperature selective catalytic reduction (SCR) activity and resistance to SO2 poisoning. In this paper, the surface properties of Tm-doped MnCeTiOX catalysts were studied and analysed by means of BET, XRD, SEM, NH3-TPD, H2-TPR and XPS. The catalyst performance was tested by using simulated flue gas. The results show that Tm doping can effectively inhibit the crystallization degree of TiO2, increase the catalyst specific surface area, and make the elements distribute more uniformly on the catalyst surface. Meanwhile, the amount of Brønsted acid sites could be increased by Tm doping. It also increased the concentration of surface adsorbed oxygen and the ratio of Mn4+/Mn and Ce3+/Ce. Therefore, the activity of the catalyst was improved by Tm doping in the temperature range of 90 °C to 270 °C, the catalyst activity remained above 97% in the temperature range of 180 °C to 270 °C. And the catalyst activity remained above 88% after a 10 h-SO2 poisoning test. Tm doping could effectively inhibit SO2 poisoning of the catalyst and reduce the adsorption of SO2 on the catalyst surface.

Unraveling the structure and role of Mn and Ce for NOx reduction in application-relevant catalysts

Mn-based oxides are promising for the selective catalytic reduction (SCR) of NOx with NH3 at temperatures below 200 °C. There is a general agreement that combining Mn with another metal oxide, such as CeOx improves catalytic activity. However, to date, there is an unsettling debate on the effect of Ce. To solve this, here we have systematically investigated a large number of catalysts. Our results show that, at low-temperature, the intrinsic SCR activity of the Mn active sites is not positively affected by Ce species in intimate contact. To confirm our findings, activities reported in literature were surface-area normalized and the analysis do not support an increase in activity by Ce addition. Therefore, we can unequivocally conclude that the beneficial effect of Ce is textural. Besides, addition of Ce suppresses second-step oxidation reactions and thus N2O formation by structurally diluting MnOx. Therefore, Ce is still an interesting catalyst additive.

Ce1−xFexVO4 with Improved Activity for Catalytic Reduction of NO with NH3

A series of Ce1−xFexVO4 (x = 0, 0.25, 0.50, 0.75, 1) catalysts prepared by modified hydrothermal synthesis were used for selective catalytic reduction (SCR) of NOx with NH3. Among them, Ce0.5Fe0.5VO4 showed the highest catalytic activity. The catalysts were characterized by X-ray diffraction (XRD), N2 adsorption–desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray fluorescence (XRF), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction using H2 (H2-TPR), and temperature-programmed desorption of NH3 (NH3-TPD). The results indicated the formation of Ce-Fe-V-O solid solutions. The average oxidation states (AOS) of Ce, Fe, V, and O atoms changed obviously with the incorporation of Fe3+ into CeVO4, and the acidity of Ce0.5Fe0.5VO4 differs from that of CeVO4 and FeVO4. The presence of more acid sites and a sharp increase in active oxygen species in Ce0.5Fe0.5VO4 effectively improved the selective catalytic reduction (SCR) activity.

Abatement of Nitrogen Oxides via Selective Catalytic Reduction over Ce1-W1 Atom-Pair Sites.

Environmentally benign CeO2-WO3/TiO2 catalysts are promising alternatives to commercial toxic V2O5-WO3/TiO2 for controlling NOx emission via selective catalytic reduction (SCR), but the insufficient catalytic activity of CeO2-WO3/TiO2 catalysts is one of the obstacles in their applications because of a lack of an in-depth understanding of the CeO2-WO3 interactions. Herein, we design a Ce1-W1/TiO2 model catalyst by anchoring Ce1-W1 atom pairs on anatase TiO2(001) to investigate the synergy between Ce and W in SCR. A series of characterizations combined with density functional theory calculations and in situ diffuse-reflectance infrared Fourier-transform experiments reveal that there exists a strong electronic interaction within Ce1-W1 atom pairs, leading to a much better SCR performance of Ce1-W1/TiO2 compared with that of Ce1/TiO2 and W1/TiO2. The Ce1-W1 synergy not only shifts down the lowest unoccupied states of Ce1 near the Fermi level, thus enhancing the abilities in adsorbing and oxidizing NH3 but also makes the frontier orbital electrons of W1 delocalized, thus accelerating the activation of O2. The deep insight of the Ce-W synergy may assist in the design and development of efficient catalysts with an SCR activity as high as or even higher than V2O5-WO3/TiO2.

Doping regulation increased SCR activity, selectivity, and hydrothermal stability of Mn-based cordierite catalyst

Mn-based catalyst is widely investigated in selective catalytic reduction (SCR) of nitrogen oxide (NO), and shows high NO conversion at low temperatures. However, most reports emphasize on powder catalyst instead of monolithic one. In this work, Mn-containing cordierite honeycomb and CeWFe co-doping comparisons were synthesized and applied in SCR. As a result, MnCeWFe showed the best catalytic activity, selectivity, temperature window, and hydrothermal stability. It removed 90.4% of NO together with a selectivity of 97.7% at 150 °C, and removed over 90% of NO from 150 °C to 250 °C. Even after a hydrothermal treatment, the activity of MnCeWFe was only decreased from 90.4% to 75.4% at 150 °C. In comparison, the activity of Mn was decreased from 60.7% to 32.4%. According to X-ray photoelectron spectroscopy and Diffuse Reflection Fourier Transform Infrared, CeWFe co-doping made the ratio between Mn3+ and Mn4+ close to 1:1, maintained this ratio under hydrothermal environment, and carried out SCR by both Eley-Rideal and Langmuir-Hinshelwood mechanisms, thus resulting in good performances. This work is in favor of developing an effective catalyst for industrial application.

Boosting low-temperature selective catalytic reduction of NO with NH3 of V2O5/TiO2 catalyst via B-doping

A series of B-doped V2O5/TiO2 catalysts has been prepared the by sol-gel and impregnation methods to investigate the influence of B-doping on the selective catalytic reduction (SCR) of NOx with NH3. X-ray diffraction, Brunauer-Emmett-Teller specific surface area, scanning electron microscope, X-ray photoelectron spectroscopy, temperature-programmed reduction of H2 and temperature-programmed desorption of NH3 technology were used to study the effect of the B-doping on the structure and NH3-SCR activity of V2O5/TiO2 catalysts. The experimental results demonstrated that the introduction of B not only improved the low-temperature SCR activity of the catalysts, but also broadened the activity temperature window. The best SCR activity in the entire test temperature range is obtained for VTiB2.0 with 2.0% doping amount of B and the NOx conversion rate is up to 94.3% at 210 °C. The crystal phase, specific surface area, valence state reducibility and surface acidity of the active components for the as-prepared catalysts are significantly affected by the B-doping, resulting in an improved NH3-SCR performance. These results suggest that the V2O5/TiO2 catalysts with an appropriate B content afford good candidates for SCR in the low temperature window.

Effects of MoOx on dispersion of vanadia and low-temperature NH3-SCR activity of titania supported catalysts: Liquid acidity and steric hindrance

Monometallic (V/TiO2 and Mo/TiO2) and bimetallic (V-Mo/TiO2) catalysts were prepared for selective catalytic reduction (SCR) of NOx with NH3 at low temperatures (100–300 °C). The effect of MoOx on the dispersion of vanadia with different V2O5 loadings was investigated on the basis of X-ray diffraction (XRD), inductively coupled plasma optical emission spectrometry (ICP-OES), N2 adsorption–desorption, Raman spectroscopy, ultraviolet–visible (UV–Vis) spectroscopy, X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). As the molybdenum precursor, NH4Mo7O24 increased the solution acidity and promoted polymerization of VOx in liquid phase. At a low vanadia loading, polymerization of VOx, the adsorption rate of NH3 and transformation of active intermediate species NH2 were enhanced by adding MoOx, while at a high vanadia loading, the steric hindrance became dominant leading to the formation of crystalline V2O5 and MoO3 and caused decline in SCR activity.

Effect of redox promoters (CeOx and CuOx) and surface sulfates on the selective catalytic reduction (SCR) of NO with NH3 by supported V2O5-WO3/TiO2 catalysts

A series of TiO2-supported MOx catalysts (M=V, W, Ce, Cu and S) were investigated for their SCR activity. In situ Raman spectroscopy indicated that the supported MOx phases were completely dispersed as surface sites on the TiO2 support. In situ IR revealed that surface VOx, WOx and SOx sites anchored at both CeOx/CuOx and TiO2 sites. The number of surface Lewis acid sites decreased with the addition of basic (CeOx/CuOx) and acidic (VOx/WOx) sites in all catalysts, and acidic SOx in the unpromoted and Ce-promoted catalysts. The surface VOx, WOx and SOx sites introduced surface Brønsted acid sites. The redox promoters increased the NO conversion, but SOx impregnation inhibited their effect due to acid (SOx)-base (CeOx/CuOx) interactions. The SCR reaction was shown to efficiently proceed via either surface NH3* or NH4+* species, resolving the long-standing dispute on the involvement of these species in the SCR reaction.

Boosting low temperature De-NOx performance and SO2 resistance over Ce-doped two dimensional Mn-Cr layered double oxide catalyst

In this paper, Mn-Cr mixed oxides with different structures are prepared by a co-precipitation method and used as active catalysts for low-temperature NH3 selective catalytic reduction (SCR) of NO. The Mn-Cr layered structure catalyst shows the highest activity and SO2 resistance in SCR. Furthermore, a Ce doping process on the catalyst further improves the NH3-SCR activity with SO2 resistance. The features of unique texture property, acidity, reducibility, and Mn-Cr redox cycle in the derived Mn-Cr layered structure catalyst should contribute to the improved catalytic activity for the SCR. The SO2 resistance of the catalyst is also improved by suppressing manganese sulfate formation. The improved catalytic activity and SO2 resistance due to the reducibility and sulfur resistance of Ce suggest that the Ce-doped Mn-Cr layered structure catalyst could be used as an effective catalyst for NH3-SCR.

Ordered Mesoporous Tio2 Framework Confined Cesn Catalyst Exhibiting Excellent High Activity for Selective Catalytic Reduction of No with Nh3 at Low Temperature

Ordered Mesoporous Tio2 Framework Confined Cesn Catalyst Exhibiting Excellent High Activity for Selective Catalytic Reduction of No with Nh3 at Low Temperature

Manganese oxide nanorod catalysts for low-temperature selective catalytic reduction of NO with NH3.

MnOx nanorod catalysts were successfully synthesized by two different preparation methods using porous SiO2 nanorods as the template and investigated for the low-temperature selective catalytic reduction (SCR) of NO with NH3. The catalysts were characterized by scanning electron microscopy, transmission electron microscopy, nitrogen adsorption, X-ray diffraction, X-ray photoelectron spectroscopy, and NH3 temperature-programmed desorption. The results show that the obtained MnOx-P nanorod catalyst prepared by redox precipitation method exhibits higher NO removal activity than that prepared by the solvent evaporation method in the low temperature range of 100–180 °C, where about 98% NO conversion is achieved over MnOx(0.36)-P nanorods. The reason is mainly attributed to MnOx(0.36)-P nanorods possessing unique flower-like morphology and mesoporous structures with high pore volume, which facilitates the exposure of more active sites of MnOx and the adsorption of reactant gas molecules. Furthermore, there is a lower crystallinity of MnOx, higher percentage of Mn4+ species and a large amount of strong acid sites on the surface. These factors contribute to the excellent low-temperature SCR activity of MnOx(0.36)-P nanorods.

Comparison of physicochemical properties and selective catalytic reduction activities of CeMn/TiO2 catalysts with and without phosphorus additives

Lubricant additives contain phosphorus, which has a fly ash effect. Phospho-rus negatively affects catalyst activity. Determining the effects of phosphorus loading amount on the catalytic activity is important for the development of cata-lysts with high NOx reduction. This study focuses on the control of NOx emissions, one of the air pollutants released from the diesel engine. The catalysts used in the reduction of NOx emis-sions were synthesized by washcoating method. Ce and Mn contents of all cata-lysts were adjusted as 3%, while the phosphorus contents of poisoned catalysts were adjusted as 0.5% and 1%. For this purpose, cordierite with high surface area was used. The catalysts were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Brunauer-Emmett-Teller (BET), X-Ray diffraction (XRD) and ultraviolet visible spectroscopy (UV-Vis) analyzes. The NOx reduction activity of with and without phosphorus doped CeMn/TiO2 catalysts was investigated with the designed selective catalytic reduction system (SCR). NOx conversion ratios of the CeMn/TiO2 catalyst reached the high values of 84.6% at 280 °C. After the phosphorus loading, the structure of the CeMn/TiO2 catalyst deteriorated, and the NOx conversion ratios decreased. 0.5P-CeMn/TiO2 and 1P-CeMn/TiO2 catalysts showed lower NOx conversion ratios compared to CeMn/TiO2 catalyst. CeMn/TiO2 catalyst was found highly active for SCR at all tests. Phosphorus loading caused deactivation of the catalyst and deactivation increased due to the increase in phosphorus loading amount.