SCR Reaction Research Articles

Improved surface acidity of CeO2/TiO2 catalyst by Cu doping to enhance the SCR catalytic activity

The catalyst is based on CeO2 cannot be widely used in SCR reaction because of its poor NH3 adsorption performance. In this study, Cu-doped CeTi catalyst was designed. The results show that the CeTiCu0.3 has a wide active temperature window of 200–450 °C in NH3-SCR reaction, and NO conversion is > 80%. This is mainly due to the fact that Cu doping provides more acidic sites on the surface of CeTi catalyst, especially the increase of Lewis acid sites is more obvious. NH3-TPD showed that CeTiCu0.3 had a large NH3 adsorption capacity and was mainly adsorbed at Lewis acid sites. In situ DRIFTs results show that NH3 first adsorbs on the Lewis acid site of catalyst in coordination state and reacts with gaseous NOx, while NOx adsorbed on catalyst surface has low reactivity. Therefore, the CeTiCu0.3 catalyst is mainly controlled by the Eley–Rideal mechanism. More Lewis acid sites, and abunda nt Cu2+/Cu+ and Ce4+/Ce3+ formed Cu2+, Ce3+ and surface reactive oxygen species are the main reasons for the excellent catalytic performance of CeTiCu.

Insights into the mechanism of enhancing resistance of MnAlOx-Str NH3-SCR catalyst derived from streptomycin waste residue and LDHs

Streptomycin waste residue composited with Layered double hydroxides (LDHs) derived Mn1Al1Ox-Str-2 catalyst was proposed for NH3 selective catalytic reduction (NH3-SCR) denitration technology, which improved the overall catalytic performance. In the wide temperature range of 150-300℃, the preferred Mn1Al1Ox-Str-2 catalyst had Nitrogen oxides (NOx) conversion of exceeded 96%, which was higher than that of the control Mn1Al1Ox and Mn/Al2O3 catalysts. In addition, Mn1Al1Ox-Str-2 catalyst had better resistance to SO2 and/or H2O, as well as good regeneration ability. Various analytical techniques had confirmed that the Mn1Al1Ox-Str-2 catalyst derived from streptomycin residue composite LDHs precursor had better surface properties with more active species, abundant surface oxygen, higher reduction capacity and better adsorption of NOx and NH3. Analytical techniques revealed that the Lewis acid site on the surface of Mn1Al1Ox-Str-2 catalyst was involved in SCR reaction and both the Eley-Rideal mechanism and Langmuir-Hinshelwood mechanism existed simultaneously in the NH3-SCR reaction, and SO2 had a weak effect on the adsorption of reactants with fewer sulfate species formation. This work provided feasible strategies for efficient and stable SCR technology and efficient utilization of streptomycin residue waste resources, which was significant for the design and application of SCR technology in the future.

Deactivation Mechanism of Potassium on the γ-Fe2O3 Catalysts for SCR Reaction: A DFT Study

Deactivation Mechanism of Potassium on the γ-Fe2O3 Catalysts for SCR Reaction: A DFT Study

Calcium-Poison-Resistant Cu/YCeO2-TiO2 Catalyst for the Selective Catalytic Reduction of NO with CO and Naphthalene in the Presence of Oxygen.

The pollution from industrial processes based on biomass combustion is still an ongoing problem. In the present contribution, the selective catalytic reduction of NO with CO and naphthalene is carried out in the presence of 10% oxygen. The accumulation of alkaline and alkaline earth metals during biomass combustion is here simulated by the addition of calcium to a Cu-impregnated YCeO2-TiO2 support. The results show that a high dispersion of copper is obtained, which is resistant to the accumulation of calcium. Full conversion of CO and naphthalene is achieved above 200 °C, whereas NO conversions of 80, 90, and 87% are obtained for the catalysts with Ca loadings of 2.6, 5.2, and 13%, respectively, at 350 °C. It is proposed that the high activity of the catalysts is ascribed to the formation of Cu-Ox-Ce species and that the accumulation of Ca acts as a barrier to avoid copper sintering. It was found that different forms of carbonate and nitrite/nitrate species form during reaction, coexisting as adsorbed species during the SCR reaction. The selectivity to N2 was almost 100% in all cases, due to the small presence of NO2 in the reactor outlet (no N2O was detected in any conditions).

Influence of Catalyst Structural Remodelling on The Performance of NH3‐SCR Reactions: A Mini Review

AbstractWith the continuous expansion of industrial activities worldwide, industrial emissions of nitrogen oxides (NOx) pose a serious threat to both ecosystems and human health. Ammonia selective catalytic reduction of NO (NH3‐SCR) technology has emerged as the most effective means to reduce NOx emissions, and the development of catalysts is crucial for the successful implementation of this technology. In gas‐solid multiphase catalytic systems, the performance limitations of conventional catalysts can be effectively overcome by meticulously designing the nanostructures of the catalysts to achieve improved catalytic efficiency. In this review, the unique structural features of core‐shell structures, layered double hydroxide (LDHs), hollow nano spheres and nanotubes, along with their preparation processes, are systematically examined, beginning with the effects of structural changes on catalytic performance. Based on this review, the impact of structural modifications on the catalytic efficiency of the catalysts for the NH3‐SCR reaction and their anti‐poisoning performance were investigated. Ultimately, the influence of catalyst structural changes on the future design of catalysts is anticipated. This provides a robust scientific foundation for the conception of higher performance catalysts, paving the way for technological innovation and advancements in NOx emission reduction practices.

The impact of energy flow on catalytic behavior in advanced DOC+SCR emission control systems

To further improve the catalytic efficiency of the aftertreatment system in exhaust conditions, the exhaust decoupling system is employed to investigate the effect of energy flow on aftertreatment catalytic systems (SCR & DOC+SCR) at wide engine load conditions (10–100 %). The physicochemical properties of particulate matter (PM) are analyzed by transmission electron microscopy (TEM). Furthermore, the energy flow and catalytic performances under the World Harmonized Transient Cycle(WHTC) are revealed. The research results exhibited that the energy distribution of exhaust in “DOC+SCR” was 10–15 % higher than that in “SCR” under steady state conditions, the provision of additional activation energy enhances the catalytic reaction, thereby improving the rate of the reaction, particularly in terms of NOx catalytic efficiency. On the other side, under transient conditions, the energy distribution of exhaust in “DOC+SCR” was 8.72 % higher than that in “SCR”. The NO/NO2 ratio remains stable value after the exhaust passing through DOC, thereby promoting the formation of rapid SCR reaction conditions. By revealing the PM microstructure, DOC enhances PM’s microcrystalline tortuosity and reduces particle size, thereby improving its oxidation reaction characteristics through combined catalysis. Simultaneously, this study demonstrates that the optimized combined catalytic method holds great potential for complete PM treatment.

Transient kinetic analysis of the standard SCR reduction half cycle on Cu-SSZ-13 catalysts: Roles of temperature, hydrothermal aging and H2O feed content

Transient Response Methods (TRM) are applied to investigate the reduction half-cycle (RHC) of the Standard SCR reaction over a state-of-the-art Cu-SSZ-13 catalyst at temperatures ranging from 135 to 350°C. We assess the effects of hydrothermal aging (HTA), water feed content and temperature on the reaction redox chemistry. By testing three samples with different aging levels, we reveal the CuII reduction rate to be unaffected by HTA in the whole T-range under investigation. Kinetic analysis assesses the inhibiting role of water on the RHC, consistent with literature. As long as enough NH3 is stored on the catalyst surface, reduction transients are accurately predicted assuming a second-order dependence of the reduction rate on the copper(II) fraction, also at temperatures exceeding 200°C. Remarkably, under wet conditions the low-T CuII reduction mechanism remains the same at least up to 300°C.

New insights and reaction mechanisms in the design of catalysts for the synergistic removal of NOx and VOCs from coke oven flue gas: Dual regulation of oxidative properties and acidic sites

The acid and redox sites of the MnCo catalysts are simultaneously fine-tuned by the addition of V. A dual-function catalyst, designated as V0.5Mn5Co5, has been constructed for the synergistic removal of NOx and volatile organic compounds under coke-oven flue gas conditions, which exhibits > 95 % NOx conversion and > 80 % N2 selectivity at 180–300 °C. Meanwhile, it removes 70 % of ethylene at 240 °C. Besides it has excellent sulfur and water resistance. The characterization results indicate that this acid-redox dual sites modulation strategy appropriately weakens the oxidation capacity of the catalysts while increasing the surface acidity of the catalysts. The catalyst mainly performs SCR reaction through the E-R mechanism, and N2O is generated through the transition dehydrogenation of NH3 and NSCR reaction. Ethylene is first adsorbed on the catalyst surface then oxidized to form carbonate species, and finally decomposed to CO2. Ethylene oxidation follows the MvK mechanism. There is a competitive adsorption between NH3 and C2H4, and a mutual inhibition between the SCR reaction and the ethylene oxidation reaction. V0.5Mn5Co5 exhibits excellent synergistic removal of NOx and VOCs in coke oven flue gas compared with commercial VWTi catalysts, which indicates great promise for industrial application.

Rationally Designed Confined Structure Ce-Mn-TNTs Catalyst for Low-Temperature NH3-SCR Reaction with Superior Activity and H2O/SO2 Tolerance

Rationally Designed Confined Structure Ce-Mn-TNTs Catalyst for Low-Temperature NH₃-SCR Reaction with Superior Activity and H₂O/SO₂ Tolerance

Facile strategy to promote SO2‑resistance ability for NH3-SCR catalyst CeSnTiOx via copper sulfate-modified: Boost from a double reaction site

Constructing excellently SO2-resistence NH3-SCR catalyst is a challenge for achieving superior NOx removal efficiency at practical needs. In this work, the effect of sulfate modification on the performance of NH3-SCR on ordered mesoporous catalysts was carefully studied. The ordered mesoporous catalyst CeSnTiOx modified with copper sulfate with the weak-confined effect has been prepared successfully via vacuum impregnation. Interestingly, the NO removal efficiencies of CeSnTiOx modified with copper sulfate got greatly enhanced at 240 °C under the atmosphere of SO2, and the 5Cu-S/CeSnTiOx catalyst (5% loaded of copper sulfate) has shown excellent performance. A series of characterizations such as XRD, TEM, TG, Raman and in-situ DRIFTS of SO2 atmosphere were conducted to investigate the interactions on the catalyst surface of those reactant molecule. It was revealed that the copper sulfate-modified has realized the boost from double reaction sites (redox site and acid site) in the 5Cu-S/CeSnTiOx catalyst. The Cu-species can disturb the electron cycle of the catalyst and reduce the strong redox performance of Ce active site, which can inhibit the adsorption of SO2 effectively. Meanwhile, the S-species (from the SO42-) has changed the distribution of acid sites and the total acid content on the catalyst surface, which has realized the rapid SCR reaction. This work provides a facile but effective strategy for further design of highly efficient SO2-resistence SCR catalysts.

Amorphous Ce-Ti composite as an efficient bifunctional catalyst for deep oxidation of volatile organic compounds and selective catalytic reduction of NO

In this work, a series of Ce-Ti composite oxides with different Ti/Ce molar ratios was prepared by co-precipitation method, and investigated for the catalytic degradation of toluene and selective catalytic reduction of NO. The phase transition process between Ce species and Ti species is limited by modulating the interaction between Ce4+ and Ti4+, while a completely amorphous composite is generated with an appropriate molar ratio of Ti/Ce (1.5/1). The catalyst CeTi1.5Ox exhibits the best catalytic performance, where the values of T90 and T50 for deep degradation of toluene are 297 and 330 °C respectively at high weight hours space velocity (WHSV=120000 mL/(g⋅h)). Compared with CeO2, T90 and T50 decrease by 48 and 34 °C respectively while declining by 67 and 70 °C compared to TiO2. For the SCR reaction, CeTi1.5Ox reaches 100% NO conversion at 250 °C with WHSV=60000 mL/(g⋅h), reduced by 50 °C compared to pure CeO2. The amorphous nanostructure with highly dispersed Ce and Ti species was confirmed by transmission electron microscopy (TEM) and X-ray diffraction (XRD) characterizations. The X-ray photoelectron spectroscopy (XPS) and Raman analyses show that a large number of active Ce-O-Ti species and surface oxygen vacancies are generated due to the strong interaction between Ti4+ and Ce4+ in CeTi1.5Ox. Additionally, H2-TPR and O2-TPD further confirm that the interaction promotes the low-temperature reducibility and mobility of surface-active oxygen species. Meanwhile, in-situ DRIFTS study reveals that CeTi1.5Ox with amorphous nanostructure can dramatically enhance the dissociative and complete oxidation capacity for toluene.

Enhancement of nitric oxide reduction via CeZrOx/Cu‐SSZ‐39 hybrid catalyst: Improving activity and hydrothermal stability

AbstractThis study aimed to improve the catalytic activity and hydrothermal stability of Cu‐SSZ‐39 zeolite by coupling it with cerium zirconium oxides (CeZrOx), which possesses excellent oxidizing ability, and a hybrid catalyst CeZrOx/Cu‐SSZ‐39 was prepared. It is found that it exhibited enhanced low‐temperature activity, high‐temperature activity, and a wider effective temperature range compared to Cu‐SSZ‐39. Characterization results showed that the CeZrOx/Cu‐SSZ‐39 catalyst had a higher concentration of active Cu2+ ion species and improved redox properties, which could potentially promote the NH3‐SCR reaction. Additionally, the CeZrOx/Cu‐SSZ‐39 catalyst had increased chemisorbed oxygen species on its surface, facilitating the oxidation of NO to NO2 and enhancing the rate of the SCR reaction. Moreover, even after undergoing hydrothermal aging treatment, the CeZrOx/Cu‐SSZ‐39 catalyst exhibited superior catalytic activity and improved hydrothermal stability, surpassing the performance of Cu‐SSZ‐39. It is found the CeZrOx coupling allowed the hybrid catalyst to maintain a better specific surface area and pore structure during hydrothermal aging, resulting in reduced activity loss. Therefore, the addition of CeZrOx enhanced the NH3‐SCR activity of Cu‐SSZ‐39 zeolite, leading to improved catalytic activity and hydrothermal stability. CeZrOx/Cu‐SSZ‐39 catalyst has shown promising aspect for reducing NOx emissions from diesel vehicle exhaust.

Tuning the morphology of CoMn2O4 for efficient alkali-resistant catalytic reduction of NOx

To improve the NH3-SCR catalytic performance of CoMn2O4, we altered their geometric morphological and structural characteristics, developing the hollow spherical and hollow cubic morphologies of CoMn2O4 by employing hard-templating and self-templated strategy. The influence of catalyst morphology on NH3-SCR activities and alkali metal resistance was discussed specifically, and the physicochemical properties of fresh and used catalysts poisoned by alkali metals were investigated by XRD, FTIR, N2 physisorption, H2-TPR, NH3-TPD, XPS and in situ DRIFTS. Interestingly, the CoMn2O4 hollow spherical (CoMn2O4-S) outperformed hollow cubic (CoMn2O4-C) and the reference solid sphere with much better low-temperature activity, the widened temperature window and higher poisoning-resistant ability. Loss of acid sites, drop of active oxygen species and reducibility accounted for the poor low-temperature activity of alkali poisoned catalysts. CoMn2O4-S catalysts with abundant acid sites and hollow configuration can decelerate the process of alkali metal poisoning. With the aid of in situ DRIFTS investigation, it was confirmed that the SCR reaction over fresh or poisoned CoMn2O4 catalysts follows an Eley-Rideal (E-R) mechanism.

Activity of CuCoCe layered double hydroxides catalysts and mechanism for C3H6-SCR

CuxCoyCez-LDH prepared with layered double hydroxides (LDHs) as precursors was calcined to form CuxCoyCezO catalysts which were experimentally investigated for the selective catalytic reduction of NO by C3H6 (C3H6-SCR) in a fixed bed micro-reactor in the presence of O2. The physical–chemical properties of the catalysts were characterized and analyzed with respect to the SCR reactivity. In situ DRIFTS study was conducted to investigate the intermediate species during the SCR reaction. Results showed that NO conversion was as high as 95 % at 225 °C over Cu0.21Co0.48Ce0.31O catalyst. The excellent activity of the catalyst could be attributed to the synergistic effect between Cu, Co, and Ce. The XRD results showed that the synergistic effect between the metals was because of the formation of the solid solution between Cu, Co, and Ce, which promoted the interaction and dispersion of the three active components. EDS mapping further proved this point. According to the XPS data, Cu and Co had a redox reaction that increased the number of oxygen vacancies favorable for NO adsorption and dissociation. The redox properties between Cu and Co was further confirmed to improve the catalytic activity by H2-TPR. Additionally, the results of BET and NH3-TPD demonstrated that the SCR catalytic activity was promoted by the right quantity of acidic sites and the specific surface area. In situ DRIFTS experiments provided a mechanism for the C3H6-SCR reaction on the catalyst and confirmed the formation of reaction intermediates such as bidentate and monodentate nitrate, formate, and acetate.

Plasma-assisted manipulation of vanadia nanoclusters for efficient selective catalytic reduction of NOx

Supported nanoclusters (SNCs) with distinct geometric and electronic structures have garnered significant attention in the field of heterogeneous catalysis. However, their directed synthesis remains a challenge due to limited efficient approaches. This study presents a plasma-assisted treatment strategy to achieve supported metal oxide nanoclusters from a rapid transformation of monomeric dispersed metal oxides. As a case study, oligomeric vanadia-dominated surface sites were derived from the classic supported V2O5-WO3/TiO2 (VWT) catalyst and showed nearly an order of magnitude increase in turnover frequency (TOF) value via an H2-plasma treatment for selective catalytic reduction of NO with NH3. Such oligomeric surface VOx sites were not only successfully observed and firstly distinguished from WOx and TiO2 by advanced electron microscopy, but also facilitated the generation of surface amide and nitrates intermediates that enable barrier-less steps in the SCR reaction as observed by modulation excitation spectroscopy technologies and predicted DFT calculations.

Acid-washing-alkali-fusion pretreated red mud for fabricating Cu-based BEA zeolite for NH3-SCR

The utilization of red mud as a solid waste to fabricate high-value-added products was a critical approach to reduce its storage. This research successfully synthesized a series of Cu-based BEA zeolite NH3-SCR catalysts with the acid-washing-alkali-fusion pretreated red mud as the Al source. XRF, XRD and N2 adsorption–desorption characterized the textual information of all samples. The H2-TPR, XPS, and UV–Vis DRS characterized the electronic structure of Cu. The highest Cu2+ content was obtained in Cu-BA0.5-H among all samples. The Cu-BA0.5-H processed the excellent low-temperature NO removal performance of ca. 99 % in 200 °C ∼ 300 °C when NH3/NO was 1. Finally, the in-situ DRIFTS analysis was carried out regarding the NH3 adsorption, NO + O2 adsorption, and co-adsorption to evaluate the possible reaction route. It was confirmed that the SCR reduction over Cu-BA0.5-H in SCR reactions followed the E-R mechanism, but different critical intermediate species depended on the reaction temperatures. It was deduced that the acid-washing-alkali-fusion pretreatment made the non-water-soluble components containing Si and Al into soluble components and further affected NO removal performance of the fabricated catalysts. Our research provided a novel approach for converting red mud into high-value products and unravelled the possible mechanism for NH3-SCR.

Spatial Distribution of Brønsted Acid Sites Determines the Mobility of Reactive Cu Ions in the Cu-SSZ-13 Catalyst during the Selective Catalytic Reduction of NOx with NH3.

The formation of dimer-Cu species, which serve as the active sites of the low-temperature selective catalytic reduction of NOx with NH3 (NH3-SCR), relies on the mobility of CuI species in the channels of the Cu-SSZ-13 catalysts. Herein, the key role of framework Brønsted acid sites in the mobility of reactive Cu ions was elucidated via a combination of density functional theory calculations, in situ impedance spectroscopy, and in situ diffuse reflectance ultraviolet-visible spectroscopy. When the number of framework Al sites decreases, the Brønsted acid sites decrease, leading to a systematic increase in the diffusion barrier for [Cu(NH3)2]+ and less formation of highly reactive dimer-Cu species, which inhibits the low-temperature NH3-SCR reactivity and vice versa. When the spatial distribution of Al sites is uneven, the [Cu(NH3)2]+ complexes tend to migrate from an Al-poor cage to an Al-rich cage (e.g., cage with paired Al sites), which effectively accelerates the formation of dimer-Cu species and hence promotes the SCR reaction. These findings unveil the mechanism by which framework Brønsted acid sites influence the intercage diffusion and reactivity of [Cu(NH3)2]+ complexes in Cu-SSZ-13 catalysts and provide new insights for the development of zeolite-based catalysts with excellent SCR activity by regulating the microscopic spatial distribution of framework Brønsted acid sites.

Cu-OFF/ERI Zeolite: Intergrowth Structure Synergistically Boosting Selective Catalytic Reduction of NOx with NH3.

Cu-SSZ-13 has been commercialized for selective catalytic reduction with ammonia (NH3-SCR) to remove NOx from diesel exhaust. As its synthesis usually requires toxic and costly organic templates, the discovery of alternative Cu-based zeolite catalysts with organotemplate-free synthesis and comparable or even superior NH3-SCR activity to that of Cu-SSZ-13 is of great academic and industrial significance. Herein, we demonstrated that Cu-T with an intergrowth structure of offretite (OFF) and erionite (ERI) synthesized by an organotemplate-free method showed better catalytic performance than Cu-ERI and Cu-OFF as well as Cu-SSZ-13. Structure characterizations and density functional theory calculations indicated that the intergrowth structure promoted more isolated Cu2+ located at the 6MR of the intergrowth interface, resulting in a better hydrothermal stability of Cu-T than Cu-ERI and Cu-OFF. Strikingly, the low-temperature activity of Cu-T significantly increased after hydrothermal aging, while that of Cu-ERI and Cu-OFF substantially decreased. Based on in situ diffuse reflectance infrared Fourier transform spectra analysis and density functional theory calculations, the reason can be attributed to the fact that NH4NO3 formed on the CuxOy species within ERI polymorph of Cu-T underwent a fast SCR reaction pathway with the assistance of Brønsted acid sites at the intergrowth interfaces under standard SCR reaction conditions. Significantly, Cu-T exhibited a wider temperature window at a catalytic activity of over 90% than Cu-SSZ-13 (175-550 vs 175-500 °C for fresh and 225-500 vs 250-400 °C for hydrothermal treatment). This work provides a new direction for the design of high-performance NH3-SCR catalysts in terms of the interplay of the intergrowth structure of zeolites.

An in-depth revelation of a novel facilitation mechanism of H2O on the NH3-SCR reaction of Mn-Ce/TiO2 catalyst with exposed anatase {001} facets

H2O typically has a detrimental impact on the NH3-SCR reaction, exacerbating the sulfur poisoning of the catalysts. This study thoroughly explores the unusual facilitating mechanism of H2O (gas) (g) at low concentrations (volume fraction less than 3.5 vol%) on the NH3-SCR reaction of a Mn-Ce/TiO2 (M−C/Ti) catalyst with preferential exposure of the anatase {001} facets (M−C/Ti-001) through comprehensive experimental characterization and DFT (Density functional theory) calculations. The optimum water vapor promotion concentration of 2.5 vol% was experimentally determined. It generated new Brønsted acid sites after H2O adsorption on the anatase {001} facets, increasing the activity of the Lewis acid sites and the NH3 adsorption capacity on Brønsted acid sites (B-NH4+). B-NH4+ species can react with NO2 in a fast SCR reaction, significantly enhancing the overall reaction rate. The low content of H2O (g) contributes to the inert linear nitrite involved in the NH3-SCR reaction, which is favourable for the NH3-SCR reaction. In addition, the Brønsted acid sites effectively inhibited the adsorption of SO2 onto the surface of the M−C/Ti-001 catalyst, enhancing its sulfur resistance. This study provides new insights into the promotion mechanism of M−C/Ti-001 catalysts by low concentration of water vapor.

New insights into the various SCR performances of the CeOx-FeOx mixed-oxide catalysts prepared using different iron precursors

This article illustrated the effects of iron precursors on the deNOx performance of the CeOx-FeOx catalysts. With regard to the catalyst prepared using Fe(NO3)3 as the iron precursor (CeFe–N), relatively poor deNOx performance was observed; <80% NOx conversion was obtained at 130–450 °C. While for the samples synthesized using FeCl3 and Fe2(SO4)3 as the iron sources (CeFe–C and CeFe–S), >90% of the NOx was effectively removed from the working gas in the temperature range of 230–350 °C and >270 °C, respectively, signifying the broadened operational temperature range. The superior oxidative ability of metal cations primarily contributed to a low activation energy, which was favorable for the activation of the reactants and the acceleration of the reaction via the "fast SCR" pathway at lower temperatures. Meanwhile, a comparatively low availability of the surface acid sites signified the limited adsorption of NH3, which thus endowed CeFe–N with a low pre-exponential factor and primarily caused the restrained proceeding of the SCR reaction. In contrast, the presence of ample acid sites and the weakened oxidative ability of metal cations successively explained the increased pre-exponential factor and activation energy of CeFe–C and CeFe–S. The synergistic effects of the previously indicated two factors enabled these two catalysts to have a higher or similar low-temperature NOx conversion compared with CeFe–N. With increasing the temperature, the additional generation of NOx was favored over CeFe–N, causing a decline in its NOx conversion efficiency. On the contrary, the inhibited proceeding of NH3 over-oxidation ensured most NH3 to serve as the reductant to reduce NOx on CeFe–C and CeFe–S, which mainly explained their comparatively broad operational temperature window.