NH3-SCR Oxidation Research Articles

Enhanced low-temperature activity of Mn-based catalysts for NH3 selective catalytic reduction of NO through Ce-modulated redox and TiO2 shell construction

Manganese-based catalysts presented great challenges for the wide operating window in the selective catalytic reduction of NOx with NH3 (NH3-SCR). Aiming at enhancement of the SCR performance, a series of MnCeOx (MnyCe1) and Mn1Ce1@TiO2 catalysts were prepared. Impressively, the Mn1Ce1 catalyst exhibited excellent low-temperature activity, achieving over 80 % conversion of NO within the temperature range of 85–350 °C, but the N2 selectivity decreased with the increasing temperature. Upon coating a TiO2 shell, the temperature window with N2 selectivity exceeding 80 % was significantly widened to 85–350 °C since the weak redox ability limited the NH3 oxidation to undesired N2O. High surface area, together with abundant acid sites and chemical adsorbed oxygen that formed via the interaction between Mn4+/Mn3+, Ce4+/Ce3+ and Ti4+/Ti3+, contributed to the superior catalytic performance of Mn1Ce1@TiO2. In addition, through in situ DRIFTS analysis, both Eley-Rideal and Langmuir-Hinshelwood reaction routes were observed. This work would provide an efficient and low-cost strategy for preparing Mn-based catalysts with excellent low-temperature activity for NOx removal.

Simultaneously accomplishing selective catalytic reduction of NO and catalytic oxidation of CO in a catalyst coupling system

Considering that nitrogen oxides (NOx) and carbon monoxide (CO) usually meantime exist in industrial flue gas, it is meaningful to develop a collaborative control technology for the simultaneous purification of NOx and CO. In this work, the catalysts xCu-1V-5W/Ti were evaluated in the simultaneously selective catalytic reduction by NH3 (NH3-SCR) and CO oxidation. The introduction of CuO provided the active sites for the oxidation of CO, while inhibited the NH3-SCR process and facilitated the generation of N2O by-product at high temperature. Accordingly, a catalyst coupling system was designed by employing 1V-5W/Ti and 2Cu-1V-5W/Ti catalysts in one reactor, and high NO conversion (>90 %) and CO removal efficiency (>80 %) could be simultaneously realized within 350–500 °C. This work would provide valuable insights for achieving simultaneous removal of NOx and CO using the catalyst coupling method.

Study on the role of Fe species and acid sites in NH3-SCR over the Fe-based zeolites

Fe doped ZSM-5 zeolite catalysts, prepared with solution ion-exchange method, calcinated at various temperatures and aged with/without H2O, were tested for activity in the selective catalytic reduction of NOx with NH3 (NH3-SCR) and characterized by XRD, NMR, UV‐Vis, XPS, H2-TPR, NH3-TPD and in-situ DRIFTs for structure and species change to investigate the role of Fe sites and acidity in SCR reaction. The results showed that the SCR activity for the Fe-ZSM-5 was mainly dependent on the active Fe species rather than acidity. Fe-oxo related Lewis sites were important for the low temperature SCR reaction, while high Brønsted acidity was not necessary for a high SCR activity. It should be noticed that the inactive free Fe2+ ions could be converted to isolated Fe3+ species by high temperature during calcination and aging, which could be inhibited by H2O due to dealumination during hydrothermal aging. This resulted in the decreased SCR activity after aging in the presence of H2O and the improved NO conversion after high-temperature calcination and thermal aging due to that the isolated Fe3+ acted as the main active site at temperature <500 ℃. The in-situ DRIFTs study showed that NH3 adsorption on acid sites was not the necessary step for the low-temperature SCR reaction but essential to NH3 oxidation, and the Eley-Rideal (E-R) mechanism was the main pathway for standard NH3-SCR.

Promotion effect of bulk sulfates over CeO2 for selective catalytic reduction of NO by NH3 at high temperatures

Understanding the influence of sulfates over catalysts for selective catalytic reduction of NO with NH3 (NH3-SCR) is crucial due to the universal presence of SO2 in exhaust gas. Depending on the degree of sulfation, there mainly exist surface and bulk sulfates and NH3-SCR activity is generally considered to suffer more from bulk sulfates. Herein, the unique function of bulk sulfates over CeO2 in promoting high-temperature SCR reaction is revealed. Notably, compared with CeO2 dominated with surface sulfates (S-CeO2–4h) and commercial V2O5-WO3/TiO2, CeO2 with bulk sulfates (S-CeO2–72h) exhibits admirable NO conversion at the temperature range of 400–550 °C. Bulk sulfates provide more Brønsted acid sites with stronger strength for NH3 adsorption. Moreover, the oxidation ability of CeO2 is significantly inhibited due to electron-withdrawing effect from bulk sulfates, which alleviates NH3 oxidation at high temperatures. More NH3 adsorption with high stability and limited NH3 oxidation capacity ensure the excellent catalytic performance for S-CeO2–72h in high-temperature denitration. This work provides new insight of bulk sulfates in promoting SCR activity and open a new avenue to design deNOx catalysts employed at high temperatures.

High-Dispersed V2O5-CuOX Nanoparticles on h-BN in NH3-SCR and NH3-SCO Performance.

Typically, to meet emission regulations, the selective catalytic reduction of NOX with NH3 (NH3-SCR) technology cause NH3 emissions owing to high NH3/NOX ratios to meet emission regulations. In this study, V-Cu/BN-Ti was used to remove residual NOX and NH3. Catalysts were evaluated for selective catalytic oxidation of NH3 (NH3-SCO) in the NH3-SCR reaction at 200–300 °C. The addition of vanadium and copper increased the number of Brønsted and Lewis acid sites available for the reaction by increasing the ratio of V5+ and forming Cu+ species, respectively. Furthermore, h-BN was dispersed in the catalyst to improve the content of vanadium and copper species on the surface. NH3 and NOX conversion were 98% and 91% at 260 °C, respectively. Consequently, slipped NH3 (NH3-Slip) emitted only 2% of the injected ammonia. Under SO2 conditions, based on the NH3 oxidation reaction, catalytic deactivation was improved by addition of h-BN. This study suggests that h-BN is a potential catalyst that can help remove residual NOX and meet NH3 emission regulations when placed at the bottom of the SCR catalyst layer in coal-fired power plants.

Effect of Cu loading content on the catalytic performance of Cu-USY catalysts for selective catalytic reduction of NO with NH3

Series of Cu-USY zeolite catalyst with different Cu loading content were synthesized through simple impregnation method. The obtained catalysts were subjected to selective catalytic reduction of NOx with NH3 (NH3-SCR) performance evaluation, structural/chemical characterizations such as X-ray diffraction (XRD), N2 adsorption/desorption, H2 temperature-programmed reduction (H2-TPR), NH3 temperature-programmed desorption (NH3-TPD) as well as detailed in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments including CO adsorption, NH3 adsorption and NO+O2 in situ reactions. Results show that Cu-USY with proper Cu loading (in this work 5Cu-USY with 5 wt.% Cu) could be promising candidates with highly efficient NH3-SCR catalytic performance, relatively low byproduct formation and excellent hydrothermal stability, although its SO2 poisoning tolerability needs alleviation. Further characterizations reveal that such catalytic advantages can be attributed to both active cu species and surface acid centers evolution modulated by Cu loading. On one hand, Cu species in the super cages of zeolites increases with higher Cu content and being more conducive for NH3-SCR reactivity. On the other hand, higher Cu loading leads to depletion of Brønsted acid centers and simultaneous formation of abundant Lewis acid centers, which facilitates NH4NO3 reduction via NH3 adsorbed on Lewis acid centers, thus improving SCR reactivity. However, Cu over-introduction leads to formation of surface highly dispersed CuOx, causing unfavorable NH3 oxidation and inferior N2 selectivity.

Promotional effect of Ce in NH3-SCO and NH3-SCR reactions over Cu-Ce/SCR catalysts

Commercial V-W-Ti catalysts were modified with Cu and different contents of Ce to remove slip ammonia and remaining nitrogen oxide from the end stage of SCR technology. The activities of NH3 oxidation by O2 (NH3-SCO) and NO reduction by NH3 (NH3-SCR) of these catalysts were examined from 150 to 400 ℃. The consequences indicated that the addition of Ce and Cu could considerably enhance NH3 oxidation and NO reduction capacity of the catalysts and Ce was conducive to reduce the detrimental effects of H2O and SO2. The characterization tests indicated that the surface active oxygen increased because of the interaction between V, Cu and Ce. Moreover, the loaded Ce and Cu contributed to enhance the surface acidity and redox property of SCR catalysts.

Experimental and kinetic modeling study for N2O formation of NH3-SCR over commercial Cu-zeolite catalyst

In this paper, a systematic experimental and kinetic model investigation was conducted over Cu-SSZ-13 catalyst to study the DeNOx efficiency and N2O formation for selective catalytic reduction of NOx with NH3 (NH3-SCR). The kinetic model was developed for various reactions to take place in the NH3-SCR system, including NH3 adsorption/desorption, NH3 oxidation, NO oxidation, standard SCR, fast SCR, slow SCR and N2O formation reactions. In addition, the reaction of N2O formation from NH3 non-selective oxidation was taken into account. All the experiments were performed in a flow reactor with a feed stream near to the real application of diesel engine vehicles exhaust. The current model can satisfactorily predict the steady state conversion rate of various species at the reactor outlet and the effect of gas hourly space velocities and ammonia nitrogen ratio on N2O formation. The results show that the kinetic model can simulate the reaction process of the Cu-SSZ-13 catalyst well. This is significant for the optimization of NH3-SCR system for achieving the higher DeNOx efficiency and the lower N2O emission.

Cu-IM-5 as the Catalyst for Selective Catalytic Reduction of NOx with NH3: Role of Cu Species and Reaction Mechanism

The role of Cu species in Cu ion-exchanged IM-5 zeolite (Cu-IM-5) regarding the performance in selective catalytic reduction (SCR) of NOx with NH3 (NH3-SCR) and the reaction mechanism was studied. Based on H2 temperature-programmed reduction (H2-TPR) and electron paramagnetic resonance (EPR) results, Cu–O–Cu and isolated Cu species are suggested as main Cu species existing in Cu-IM-5 and are active for SCR reaction. Cu–O–Cu species show a good NH3-SCR activity at temperatures below 250 °C, whereas their NH3 oxidation activity at higher temperatures hinders the SCR performance. At low temperatures, NH4NO3 and NH4NO2 are key reaction intermediates. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) suggests a mixed Eley–Rideal (E–R) and Langmuir–Hinshelwood (L–H) mechanism over Cu-IM-5 at low temperatures.

Environmental Reactions of Air-Quality Protection on Eco-Friendly Iron-Based Catalysts

A series of iron functionalized hydroxyapatite (Fe/HAP) samples with different metal loading (2 &lt; wt.% Fe &lt; 13) was prepared by a flash ionic exchange procedure from iron(III) nitrate as precursor and tested in some environmental air-quality protection reactions such as the catalytic reduction of NOx by NH3 (NH3-SCR), catalytic oxidation of NH3 (NH3-SCO) and catalytic N2O decomposition. The catalytic performances of the Fe/HAP catalysts were determined under flow conditions as a function of temperature and using reactant concentrations typical of polluting gaseous emissions from industrial vents. Physico-chemical characterization with various techniques of study (UV-DR and Mössbauer spectroscopies, NH3 titration, N2-physisorption, and XRPD analyses) provided valuable information on Fe-speciation, acidity, morphology, and structure of the samples. In general, highly dispersed Fe3+ centers were the predominant species, irrespective of Fe-loading, while just low percentage (≤15%) of FexOy nanoclusters (2 &lt; size/nm &lt; 4) was detected on the samples. As expected, the differences in iron concentration produced a diversified effect of both catalyst properties and catalytic activity, comprising the conversion and selectivity profiles, different for each reaction considered. The obtained results indicate a good potentiality for the eco-friendly Fe-catalysts for some environmental reactions of air protection.

Adjustment of operation temperature window of Mn-Ce oxide catalyst for the selective catalytic reduction of NOx with NH3

In order to enhance the catalytic activity of Mn-Ce oxide catalyst for the selective catalytic reduction of NOx with NH3 (NH3-SCR), W was introduced as a promoter. With the doping of W, the NOx conversion over Mn3CeOx catalyst above 150 °C was increased, and the N2O production was significantly decreased. Even in the present of water vapour, Mn3CeW0.3Ox still showed a good SCR activity. H2-TPR and XPS results suggested that the doping of tungsten could inhibit the charge imbalance and reducibility, which would inhibit NO oxidation to NO2 over Mn3CeOx. As a result, the NOx conversion below 150 °C over Mn3CeW0.3Ox was slightly lower than that over Mn3CeOx. Since the NOx production and the NH3 conversion during the NH3 oxidation of Mn3CeOx were inhibited after the doping of W, the NOx conversion above 150 °C over Mn3CeW0.3Ox was higher than that over Mn3CeOx. The transient reaction demonstrated that the doped W species on Mn3CeW0.3Ox could inhibit the N2O produced by the Langmuir-Hinshelwood mechanism. Kinetic study proved that νSCR over Mn3CeW0.3Ox was obviously higher that over Mn3CeOx, νNSCR and νC-O over Mn3CeOx were much higher than those of Mn3CeW0.3Ox, which were consistent with the SCR activity.

Relationships between copper speciation and Brønsted acidity evolution over Cu-SSZ-13 during hydrothermal aging

To investigate possible relationships between copper speciation and Brønsted acidity evolution during hydrothermal aging, a series of aged Cu-SSZ-13 catalysts were prepared by varying aging temperatures from 550 to 850 °C. Besides selective catalytic reduction of NOx by NH3 (NH3-SCR), NH3 oxidation was also adopted as a probe reaction. The catalysts were characterized by H2 temperature-programmed reduction (H2-TPR), in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and magic angle spinning nuclear magnetic resonance (MAS NMR). Isolated Cu ions protect Si-O(H)-Al sites against hydrothermal cleavage, but aggregated Cu species are found to destroy the zeolite framework. Due to the instability of ZCuOH (Z represents negatively charged zeolite [Si-O-Al]– site) at 8-member ring sites, mild hydrothermal aging induces the migration of metastable [Cu(OH)]+ ions to unsaturated 6-member ring sites to form Z2Cu, and excess [Cu(OH)]+ ions start to aggregate at 700 °C. The formation of two types of aggregated Cu species, CuAlOx and CuOx, and their roles in SCR reaction were distinguished. The former one originates from the combination of Cu with extraframework Al and is inert, while the latter forms upon more severe aging and catalyzes over-oxidation of NH3 toward NO, which degrades high-temperature SCR activity.

A facile and controllable in situ sulfation strategy for CuCeZr catalyst for NH3-SCR

The Cu-based transition-metal-oxide catalysts were widely applied for the selective catalytic reduction of NOx with NH3 (NH3-SCR), but limited in practical application because of the inferior catalytic performance at high temperatures. To counter this issue, we designed a facile in situ strategy to obtain sulfated CuCeZr catalysts, on which the sulfation degree could be precisely controlled without any further post-treatment. The sulfated CuCeZr catalysts not only show broader SCR reaction temperature window and promoted N2 selectivity, but also demonstrate satisfactory tolerance to H2O and SO2. The outcomes indicate that stronger surface acidity, weaker reducibility and excellent stability for adsorbing NH3 on the sulfated CuCeZr catalysts greatly suppress the undesired excessive oxidation of NH3 at high temperatures, which enhance the high-temperature activity and N2 selectivity. Furthermore, the transient in situ DRIFT and steady-state kinetic studies reveal that both unsulfated and sulfated catalysts mainly follow the Eley-Rideal mechanism.

Selective catalytic reduction of NO by NH3 over Fe2O3-promoted V2O5/TiO2-based catalysts with high Fe2O3-to-V2O5 ratios

Fe2O3-promoted V2O5-WO3/TiO2 catalysts with high Fe2O3-to-V2O5 ratios (3.4–6) have been prepared for the selective reduction of NO with NH3 (NH3-SCR) and extensively characterized using various spectroscopic measurements. No crystalline iron oxides were indicated even for 8% Fe2O3-promoted V2O5-WO3/TiO2 but α-Fe2O3 crystallites were observed in a XRD pattern for 7.04 % Fe2O3-promoted WO3/TiO2. Both Raman and XPS measurements suggest the formation of FeOV species which may make a better N2 selectivity in NH3-SCR reaction at high temperatures. All Fe2O3-promoted catalysts showed a great depression on N2O formation. At temperatures >400 °C, samples with 5.46 and 8% Fe2O3 (Fe2O3/V2O5 ratio = 3.4 and 5) gave significantly lower N2O production levels compared with the unpromoted and lower Fe2O3 loading catalysts. However, increasing in Fe2O3 loading resulted in a decrease in high temperature deNOx activity due to the oxidation of NH3 into NO. All the 3.4 and 5 ratio catalysts after a hydrothermal aging at 550 °C for 10 h gave NO removal activity and N2O formation similar to those measured over non-aged ones. However, such an aging at 750 °C could lead to a considerable increase in N2O formation even for the 5.46 % Fe2O3-promoted catalyst. Fe2O3-promoted V2O5/TiO2-based catalysts could catalyze the reduction of gas-phase N2O by NH3 adsorbed strongly, suggesting that this reaction may be a major route to greatly suppress N2O formation, consistent with infrared studies showing a reaction between N2O and surface NH3 species strongly adsorbed on the catalysts. This surface reaction could readily occur from a temperature as low as 250 °C.

Effects of Ce over TiO2 supported MnOx-based Catalyst for NOx Reduction by Ammonia

Ce modified MnOx-based catalysts have attracted much attention due to its high activity for selective catalytic reduction of NOx by NH3 (NH3-SCR) at low-temperatures. However, the most important role of Ce on the NH3-SCR performance of MnOx-based catalysts has not been confirmed. Herein, the typical Ce-Mn/TiO2 catalyst was synthesized through incipient-wetness impregnation method, the positive role of Ce on Ce-Mn/TiO2 catalyst in the NH3-SCR process was revealed by combining different activity tests (including NO oxidation and NH3 oxidation) and characterizations (including XRD, XPS and He-TPDMS experiments). It was found that the introduction of Ce can promote the dispersion of MnOx on TiO2 support. Meanwhile, the doping of Ce in MnOx can also increase the content of Mn4+ species. The Mn4+ species plays a crucial role in NO oxidation reaction, which can trigger the “Fast SCR” reaction and promote the conversion of NOx. This work provides insight into the catalyst design for NH3-SCR process at low-temperature.

The balance of acidity and redox capability over modified CeO2 catalyst for the selective catalytic reduction of NO with NH3

The effect of acidity and redox capability over sulfuric acid-modified CeO2 catalysts were studied for the selective catalytic reduction of NOx with NH3 (NH3-SCR). The deposition of sulfate significantly enhanced the catalytic performance over CeO2. NOx conversion over 4H2SO4/CeO2 at 230–440 °C was higher than 90%. The strong redox capability of CeO2 could result in unselective NH3 oxidation and decrease high temperatures catalytic activity and N2 selectivity. The deposition of sulfate increased the acidity and weakened the redox capability, and then increased the high temperature NOx conversion and N2 selectivity. An appropriate level of acidity also promoted the activity at 190–250 °C over ceria-based catalysts, and with further increase in the acidity, the SCR activity decreased slightly. Weak redox capability lowered the low-temperature catalytic activity. Excellent SCR activity requires a balance of acidity and redox capability on the catalysts.

Thermal stability of Si-doped V2O5/WO3–TiO2 for selective catalytic reduction of NOx by NH3

The selective catalytic reduction of NOx with NH3 (NH3-SCR) is a very effective technology to control the emission of NOx, and the thermal stability of NH3-SCR catalyst is very important for removal of NOx from diesel engines. In this work, V2O5/WO3–TiO2 (VWT) and SiO2-doped V2O5/WO3–TiO2 (VWTSi10) catalysts were prepared by impregnation method and characterized by Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), Raman, temperature programmed reduction by hydrogen (H2-TPR), X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption by ammonia (NH3-TPD). The doping of SiO2 promotes the thermal stability of V2O5/WO3–TiO2 for NH3-SCR significantly. After calcination at 650 °C for 50 h, the operation window of 10% SiO2-doped V2O5/WO3–TiO2 is 220–480 °C, while the maximum NOx conversion on V2O5/WO3–TiO2 is about 77%. The presence of SiO2 obviously blocks the transformation of TiO2 from anatase to rutile and stabilizes the dispersion of VOx and WO3 on the surface. It is available for the existence of V4+ and the amount of surface acid sites increases, which inhabits the NH3 oxidation at the high temperature range and promotes NH3-SCR activity.

W-Modified Mn–Ti Mixed Oxide Catalyst for the Selective Catalytic Reduction of NO with NH3

A W-modified Mn–Ti mixed oxide catalyst was prepared by the homogeneous precipitation method, which was applied to the selective catalytic reduction of NO with NH3 (NH3-SCR). The introduction of W could broaden the operation temperature window of Mn0.5TiOx, and the Mn0.5W0.1TiOx showed good SCR activity at 150–350 °C (NOx conversion above 80%). The results of characterization demonstrated that W introduction improved the redox ability, inhibited the separated NO/NH3 oxidation abilities, and provided additional Brønsted and Lewis acid sites. When W was added, less NO oxidation to NO2 possibly led to the inhibition of SCR activity at low temperatures, while the increase of NH3 adsorption and inhibition of NH3 oxidation could contribute to the enhancement of high-temperature SCR activity. Meanwhile, the N2O formation in the NH3-SCR over both Mn0.5TiOx and Mn0.5W0.1TiOx mainly follow the Eley–Rideal mechanism, and the introduction of W inhibited the N2O formation.

The effect of cations (NH4+, Na+, K+, and Ca2+) on chemical deactivation of commercial SCR catalyst by bromides

Alkali and alkaline-earth metals from fly ash have a significant deactivation effect on catalysts used for selective catalytic reduction of NOx by NH3 (NH3-SCR). Bromides are considered effective additives to improve Hg0 oxidation on SCR catalysts. In this work, the effects of different bromides (NH4Br, NaBr, KBr, and CaBr2) on a commercial V2O5-WO3/TiO2 catalyst were studied. NOx conversion decreased significantly over the KBr-poisoned catalyst (denoted as L-KBr), while that over NaBr- and CaBr2-poisoned catalysts (denoted as L-NaBr and L-CaBr, respectivity) decreased to a lesser extent compared with the fresh sample. Poor N2 selectivity was observed over L-NaBr, L-KBr and L-CaBr catalysts. The decrease in the ratio of chemisorbed oxygen to total surface oxygen (Oα/(Oα + Oβ + Ow)), reducibility and surface acidity might contribute to the poor activity and N2 selectivity over L-KBr catalyst. The increased Oα ratio was conducive to the enhanced reducibility of L-CaBr. Combined with enhanced surface acidity, this might offset the negative effect of the loss of active sites by CaBr2 covering. The overoxidation of NH3 and poor N2 selectivity in NH3 oxidation should retard the SCR activity at high temperatures over L-CaBr catalyst. The increased basicity might contribute to increased NOx adsorption on L-KBr and L-CaBr catalysts. A correlation between the acid-basic and redox properties of bromide-poisoned catalysts and their catalytic properties is established.

The Role of Fe2O3 Species in Depressing the Formation of N2O in the Selective Reduction of NO by NH3 over V2O5/TiO2-Based Catalysts

Promotion of 2.73% Fe2O3 in an in-house-made V2O5-WO3/TiO2 (VWT) and a commercial V2O5-WO3/TiO2 (c-VWT) has been investigated as a cost effective approach to the suppression of N2O formation in the selective catalytic reduction of NO by NH3 (NH3-SCR). The promoted VWT and c-VWT catalysts all gave a significantly decreased N2O production at temperatures &gt;400 °C compared to the unpromoted samples. However, such a promotion led to the loss in high temperature NO conversion, mainly due to the oxidation of NH3 to N-containing gases, particularly NO. Characterization of the unpromoted and promoted catalysts using X-ray diffraction (XRD), NH3 adsorption-desorption, and Raman spectroscopy techniques could explain the reason why the promotion showed much lower N2O formation levels at high temperatures. The addition of Fe2O3 to c-VWT resulted in redispersion of the V2O5 species, although this was not visible for 2.73% Fe2O3/VWT. The iron oxides exist as a highly-dispersed noncrystalline α-Fe2O3 in the promoted catalysts. These Raman spectra had a new Raman signal that could be tentatively assigned to Fe2O3-induced tetrahedrally coordinated polymeric vanadates and/or surface V-O-Fe species with significant electronic interactions between the both metal oxides. Calculations of the monolayer coverage of each metal oxide and the surface total coverage are reasonably consistent with Raman measurements. The proposed vanadia-based surface polymeric entities may play a key role for the substantial reduction of N2O formed at high temperatures by NH3 species adsorbed strongly on the promoted catalysts. This reaction is a main pathway to greatly suppress the extent of N2O formation in NH3-SCR reaction over the promoted catalysts.