NOx Reduction Activity Research Articles

Unique κ-Ce2Zr2O8 Superstructure Promoting the NOx Adsorption-Selective Catalytic Reduction (AdSCR) Performance of the WO3/CeZrOx Catalyst.

Selective catalytic reduction of NOx by NH3 (NH3-SCR) for diesel emission control at low temperatures is still a great challenge due to the limit of the urea injection threshold and inferior SCR activity of state-of-the-art catalyst systems below 200 °C. Fabricating bifunctional catalysts with both low temperature NOx adsorption-storage capacity and medium-high temperature NOx reduction activity is an effective strategy to solve the issues mentioned above but is rarely investigated. Herein, the WO3/Ce0.68Zr0.32Ox (W/CZ) catalyst containing the κ-Ce2Zr2O8 pyrochlore structure was successfully developed by a simple H2 reduction method, not only showing superior NOx adsorption-storage ability below 180 °C but also exhibiting excellent NH3-SCR activity above 180 °C. The presence of the pyrochlore structure effectively increased the oxygen vacancies on the κ-Ce2Zr2O8-containing W/CZ catalyst with enhanced redox property, which significantly promoted the NOx adsorption-storage as active nitrate species below 180 °C. Upon NH3 introduction above 180 °C, the κ-Ce2Zr2O8-containing W/CZ catalyst showed greatly improved NOx reduction performance, suggesting that the pyrochlore structure played a vital role in improving the NOx adsorption-selective catalytic reduction (AdSCR) performance. This work provides a new perspective for designing bifunctional CeZrOx-based catalysts to efficiently control the NOx emissions from diesel engines during the cold-start process.

Deciphering H2-induced low-temperature NOx adsorption on Ag/Al2O3: Expanding the operating temperature range of ethanol-SCR system for effective NOx abatement

Despite the advantages of the catalytic reduction of NOx by hydrocarbons, typical Ag/Al2O3 suffers from limited low-temperature activity in response to cold-start periods. In this study, the promotional effect of H2 on NOx adsorption on Ag/Al2O3 was investigated to address the low-temperature NOx emissions. H2 significantly enhanced NOx accumulation on Ag/Al2O3 below 200 °C, with desorption occurring at high temperatures. The H2-temperature-programmed reduction (H2-TPR) results showed the formation of silver oxide on metallic Ag species by H2+O2, serving as the primary site for H2-induced NOx adsorption, while the single-atom Ag species (Ag+) remained nearly unchanged. Ag/Al2O3 with low Ag loading (1–2 wt%) exhibited lower NOx adsorption capacities compared to the case with high Ag loading (4 wt%) owing to the low metallic Ag content. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) studies identified diverse surface-adsorbed species related to H2-induced NOx adsorption. Nitrite, bridging nitrate, and bidentate nitrate contributed to low-temperature NOx desorption, whereas monodentate nitrate contributed to high-temperature desorption. Finally, we demonstrated exceptionally-high NOx reduction activity by synergistically combining the NOx trapping ability of Ag/Al2O3 with its deNOx capability through ethanol with H2, covering a wide temperature range of 100–350 °C under transient conditions at a high space velocity of 100,000 h−1.

Pr-modified vanadia-based catalyst for simultaneous elimination of NOx and chlorobenzene

The V2O5/TiO2 catalyst is the most concerned NH3-SCR catalytic system for simultaneous removal of NOx and chlorinated volatile organic compounds (Cl-VOCs). There is an urgent need to develop a vanadia-based catalyst with low vanadium loading and excellent low-temperature catalytic performance. In this work, the Pr and W co-doped vanadia-based catalysts were prepared by a simple impregnation method. After the doping of Pr and W, the vanadia-based catalyst exhibited the excellent catalytic activity for NOx reduction and chlorobenzene (CB) oxidation. The more abundant polymeric vanadyl species and crystalline V2O5 were observed on the PrV5W/Ti catalyst, which are contributing to NH3-SCR and CB oxidation activity. The redox capability and the amount of surface-active adsorbed oxygen of vanadia-based catalyst were improved markedly, thus promoting NH3-SCR and CB oxidation reaction on PrV5W/Ti. This catalyst is promising to be used in the muti-pollutant control reaction of NOx and VOCs.

Design of Ca-type todorokite catalysts with highly active for the selective reduction of NOx by NH3 at low temperatures

Ca-type todorokite catalysts were designed and prepared by a simple redox method and applied to the selective reduction of NOx by NH3 (NH3-SCR) for the first time. Compared with the Na-type manjiroite prepared by the same method, the todorokite catalysts with different Mn/Ca ratios showed greatly improved catalytic activity for NOx reduction. Among them, Mn8Ca4 catalyst exhibited the best NH3-SCR performance, achieving 90% NOx conversion within temperature range of 70–275°C and having a high sulphur resistance. Compared to the Na-type manjiroite sample, Ca-type todorokite catalysts possessed an increased size of tunnel, resulting in a larger specific surface area. As increased the amounts of Ca doping, the Na content in Ca-type todorokite catalysts significantly decreased, providing larger amounts of Brønsted acid sites for NH3 adsorption to produce NH4+. The NH4+ species were highly active for reaction with NO + O2, playing a determining role in NH3-SCR process at low temperatures. Meanwhile, larger amounts of surface adsorbed oxygen contained over the Ca-doping samples than that over Na-type manjiroite, promoting the oxidation of NO and fast SCR processes. Over the Ca-type todorokite catalysts, furthermore, nitrates produced during the flow of NO + O2, were more active for reaction with NH3 than that over Na-type manjiroite, benefiting the occurrence of NH3-SCR process. This study provides novel insights into the design of NH3-SCR catalysts with high performance.

Highly active alkali etching silica-modified Cu-Ce-Ti catalyst with superior water resistance for low temperature NOx reduction

In this study, Cu-Ce oxides supported on a silica modified TiO2 with post-alkali treatment (Cu-Ce/TS-am) were synthesized to enhance the catalytic activity and water resistance for low-temperature NOx reduction with ammonia. Experiment results revealed that the optimal Cu-Ce/TS-am sample possessed over 90% NOx conversion at 180–350 °C in the presence of 10 vol% water. Essentially, the formed Ti-Si strong interactions after Si addition could be responsible for that. On the one hand, the interactions increased specific surface area, total acidity and oxygen mobility, thus promoting SCR activity. On the other hand, it could enhance the hydrophobicity of the catalysts as there existed lower surface roughness, smaller particle size and enlarged mesoporous pore size after Si addition, alleviating the competitive adsorption of water with NH3. Additionally, the alkali treatment removed uncombined SiOx, which optimized the mesoporous pore structure and increased the exposure of active sites and acidic sites on the catalyst surface, further enhancing water resistance and catalytic activity. These findings could provide useful guidelines for the development of highly active SCR catalyst with well water resistance in real application.

V-Cu bimetallic oxide supported catalysts for synergistic removal of toluene and NOx from coal-fired flue gas: The crucial role of support

It is a major challenge to achieve effective synergistic reduction of NOx and VOCs in coal-fired flue gas under complex working conditions. In this work, V-Cu bimetallic oxide catalysts with different supports were designed. V1-Cu5 bimetallic oxide supported on TiO2 showed significantly higher activity for simultaneous toluene oxidation and NOx reduction than that supported on ZSM-5, SiO2 and γ-Al2O3. Meanwhile, it exhibited excellent stability and anti-poisoning performance, and could block the formation of toxic polycyclic aromatic hydrocarbons in by-products. Compared with ZSM-5, SiO2 and γ-Al2O3, TiO2 as support was conducive to the formation of abundant acidic sites and oxygen vacancies. In addition, the strong interaction between the metal active sites and TiO2 accelerated the electron transfer from Cu to adsorbed O2, thus promoting the formation of active O2−. This work can provide guidance for the development of catalysts designed for the simultaneous catalytic removal of NOx and VOCs.

Preferential chemical vapor deposition for the synthesis of the catalysts for CO mediated NOx selective catalytic reduction

In previous studies IrRu/Al2O3 has exhibited good activity for NOx reduction by CO at low temperature. The Ir-Ru alloy structure was revealed to be the origin of the outstanding activity of IrRu/Al2O3 in the CO-induced deNOx reaction. In this work, preferential chemical vapor deposition (pCVD) was applied as an effective and selective Ir-Ru alloy catalyst synthesis method, which selectively deposits Ir precursor on the pre-existing Ru nanoparticles. The synthesized IrRu/Al2O3 catalysts were characterized by transmission electron microscopy, X-ray diffraction, X-ray absorption spectroscopy, temperature programmed reduction, X-ray photoelectron spectroscopy, and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs) analyses. The results confirmed the formation of Ir-Ru alloy, and showed that Ir can be preferentially deposited on Ru surface via pCVD, rather than on the Al2O3 support. IrRu/Al2O3 synthesized by pCVD exhibited better performance in the NOx reduction by CO than catalysts prepared by the conventional impregnation method. Its catalytic activity varied with Ir content, which was precisely controllable using pCVD. The investigation of catalyst surface by DRIFT revealed that the accelerated NO dissociation is the primary reason for its excellent low-temperature activity of the IrRu/Al2O3 catalyst prepared by pCVD.

Influence of coke deposition by propene poisoning on Cu-SSZ-13 catalyst for selective catalytic reduction of NOx with NH3

In this study, Cu-SSZ-13 catalyst was prepared via ion exchange method and then treated with 1000 ppm or 2000 ppm propene (C3H6) poisoning for 20 h. The influence of coke deposition by C3H6 poisoning on Cu-SSZ-13 catalyst for selective catalytic reduction of NOx with NH3 was investigated with standard NH3-SCR conditions based upon the simulated gas experimental platform. The results showed that NOx reduction activity was slightly affected after 1000 ppm C3H6 poisoning while the NOx conversion was remarkably lower than that of fresh catalyst below 400 °C after 2000 ppm C3H6 poisoning. However, the NOx reduction activity was recovered and even mildly higher than the original level beyond 400 °C. The existence of coke deposition was confirmed by TG-DTA analysis. 2000 ppm C3H6 poisoned catalyst had more coke deposition than 1000 ppm C3H6 poisoned catalyst. XRD and BET results showed that the surface area of the catalyst was decreased by blocking the pore channels, especially for 2000 ppm C3H6 poisoned catalyst, but the structure of the catalyst was not collapsed after C3H6 poisoning. XPS and NH3-TPD results illustrated that Cu2+, CuO, Lewis and Brønsted acid sites were more susceptible to be affected under 2000 ppm C3H6 poisoning. NH3 oxidation activity was weakened slightly on poisoned catalysts above 400 °C in NH3-TPO. From the In-situ DRIFTs results, the basic mechanism of inhibition by C3H6 poisoning on Cu-SSZ-13 catalysts was attributed to less available NH3 used in SCR reaction.

Unique Compensation Effects of Heavy Metals and Phosphorus Copoisoning over NOx Reduction Catalysts.

Selective catalytic reduction (SCR) of NOx from the flue gas is still a grand challenge due to the easy deactivation of catalysts. The copoisoning mechanisms and multipoisoning-resistant strategies for SCR catalysts in the coexistence of heavy metals and phosphorus are barely explored. Herein, we unexpectedly found unique compensation effects of heavy metals and phosphorus copoisoning over NOx reduction catalysts and the introduction of heavy metals results in a dramatic recovery of NOx reduction activity for the P-poisoned CeO2/TiO2 catalysts. P preferentially combines with Ce as a phosphate species to reduce the redox capacity and inhibit NO adsorption. Heavy metals preferentially reduced the Brønsted acid sites of the catalyst and inhibited NH3 adsorption. It has been demonstrated that heavy metal phosphate species generated over the copoisoned catalyst, which boosted the activation of NH3 and NO, subsequently bringing about more active nitrate species to relieve the severe impact by phosphorus and maintain the NOx reduction over CeO2/TiO2 catalysts. The heavy metals and P copoisoned catalysts also possessed more acidic sites, redox sites, and surface adsorbed oxygen species, which thus contributed to the highly efficient NOx reduction. This work elaborates the unique compensation effects of heavy metals and phosphorus copoisoning over CeO2/TiO2 catalysts for NOx reduction and provides a perspective for further designing multipoisoning-resistant CeO2-based catalysts to efficiently control NOx emissions in stationary sources.

Bifunctional ZnCo2O4 catalyst for NOx reduction and 1,2-dichloroethane combustion

ZnCo2O4 prepared via the coprecipitation method showed an efficient bifunctional activity for both NOx reduction and 1,2-dichloroethane (DCE) oxidation. Compared with Co3O4 and ZnO, ZnCo2O4 catalyst showed best catalytic activity and stability in both NOx reduction and DCE oxidation. A maximum NOx conversion of 68.9% and complete DCE combustion were obtained at 300 and 400 °C, respectively. ZnCo2O4 catalyst exhibited the highest specific surface area (m2 g−1) and concentration of surface Co3+, which were considered as the main factors that determined its catalytic performance.

Effect of H2, H2O, and CO2 on the deNOx characteristics of a combined passive NOx adsorber and NOx reduction catalyst

AbstractThe effect of H2, H2O, and CO2 on the NOx removal characteristics of a non‐PGM material (Ag/MgO/γ‐Al2O3) is investigated, which is shown to be active for both NOx adsorption and reduction. H2O facilitates NOx adsorption at early times but inhibits it at longer times. The inhibiting effect of CO2 is observed at low temperatures and is proposed to be due to bicarbonates. However, the inhibiting effect of both H2O and CO2 decreases at higher temperatures. The formation of NO2 at low temperatures is attributed to NO oxidation, and the contribution of stored NOx to NO2 formation increases with temperature. H2O inhibits NH3 oxidation at high temperatures as well as NOx reduction by NH3‐SCR at low temperatures. However, the NOx reduction activity is not affected by CO2. H2 significantly promotes the NH3‐SCR reactions, which is attributed to the facilitation of NOx spillover from the reduced Ag sites to the support.

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.

Promotion effect of hydrogen addition in selective catalytic reduction of nitrogen oxide emissions from diesel engines fuelled with diesel-biodiesel-ethanol blends

Ethanol and palm oil biodiesel blended with diesel fuel have the potential to reduce greenhouse gas emissions, such as carbon dioxide (CO2), and can gradually decrease dependence on fossil fuels. However, the combustion products from these fuels, such as oxides of nitrogen (NOx), total hydrocarbons (THC) and particulate matter (PM), require to be examined and any beneficial or detrimental effect to the environment needs to be assessed. This study investigates the hydrocarbon selective catalyst reduction (HC-SCR) activities by the effect of combustion using renewable fuels (biodiesel-ethanol-diesel) blends and the effect of hydrogen addition to the catalyst, with the various diesel engine operating conditions. Lower values rate of heat released were recorded as the ethanol fraction increases, resulting in trade-off where, lower NOx was produced while greater concentration of carbon monoxide (CO) and THC was measured in the exhaust. Consequently, increasing the THC/NOx promoting the NOx reduction activity (up to 43%). Additionally, the HC-SCR performance was greatly heightened when hydrogen was added into the catalyst and able to improve the NOx reduction activity up to 73%. The experiment demonstrated plausible alternatives to improve the HC-SCR performance through the aids from fuel blends and hydrogen addition.

Transition metals modified commercial SCR catalysts as efficient catalysts in NH3-SCO and NH3-SCR reactions

Different transition metals were used to modify commercial V2O5-WO3-TiO2 catalysts to remove slip ammonia and residual NOx from the tail of SCR system. The performance of selective catalytic oxidation of NH3 (NH3-SCO) and selective catalytic reduction of NO by NH3 (NH3-SCR) of different catalysts at 150-400 ℃ was studied. The results showed that the loading of transition metals could significantly improve the NH3 oxidation ability of the catalysts, and the presence of NO furtherly promoted it. Cu-SCR catalyst obtained the best activity of both NH3 oxidation and NOx reduction at 350 ℃, and had excellent SO2 and H2O resistance in the presence of NO. The characterization results indicated that the transition metals enhanced the amounts of acid sites and redox ability of the catalysts. Moreover, the transition metals could increase the active oxygen and improve the catalytic performance of the catalysts by the redox reaction with V4+/V5+.

Germany's supreme court rules in Solvay's favour on patent case with Neo

Methanol has been shown to promote the hydrocarbon selective catalytic reduction of NOx with octane and toluene over 2 wt% Ag/Al2O3 catalyst for the first time. In order to understand its role in the reaction fast transient kinetic methods and in situ DRIFTS analysis have been used. The catalytic activity tests showed that the addition of methanol to the HC-SCR reaction results in a significant improvement in the low temperature activity of a Ag/Al2O3 catalyst, despite the fact that methanol on its own is not reactive for the HC-SCR reaction. This promotional effect of methanol is dependent on the concentration of added methanol and is not necessarily associated with a higher concentration of reductant in the SCR feed. The fast transient kinetic analysis has shown that at each temperature the addition of methanol enhances the conversions of both NOx and octane and the production of N2 with high selectivity in comparison with those observed with n-octane or toluene alone. This phenomenon is similar to the effect of H2 which may be associated with the release of hydrogen and ammonia during the transient switches at 250 and 300 °C. Together with the fast transient experiments, the DRIFTS results showed that NCO species are formed when introducing methanol to the n-octane-SCR feed while CN species are removed/consumed from the surfaces of the Ag catalyst. These NCO species formed by adding methanol may play a vital role in promoting the catalytic activity of NOx reduction and methanol itself can be an in situ source for hydrogen formation, which subsequently enhances the SCR reaction.

Effect of gas composition on the NOx adsorption and reduction activity of a dual-function Ag/MgO/[formula omitted]-Al2O3 catalyst

An Ag/MgO/γ-Al2O3 catalyst is developed, which can perform the dual role of a passive NOx adsorber (PNA) at low temperatures and a NOx reduction catalyst at higher temperatures. The effect of H2O and CO2, as well as various reductants such as H2, NH3, and C3H6 on its deNOx performance is investigated. The NOx storage is comparable to that obtained by Pd-based PNAs, and occurs through a spillover mechanism. The presence of H2 remarkably increases the low-temperature NOx adsorption and binding strength, and is attributed to the significant formation of nitrates as opposed to the predominant formation of nitrites in the absence of H2. Moreover, the positive effect of H2 is not related to the H2-SCR activity of the catalyst or an enhancement in the NO oxidation activity. C3H6 inhibits NOx storage, but the presence of H2 promotes it considerably. A significantly high NH3-SCR activity with negligible N2O formation is measured at 150 °C, while C3H6-SCR activity is exhibited at higher temperatures. However, the presence of NH3 does not affect the binding of NOx on the various adsorption sites, which is primarily governed by the presence of H2.

Supports materialization of Pd based catalysts for NOx removal by hydrogen assisted selective catalytic reduction in the presence of oxygen

AbstractThe Pt and Pd based bimetallic catalyst are developed to address the NOx reduction activity. For this, a series of supports containing three different amounts of CeO2−MgO (9 : 1, 3 : 1, and 3 : 2) are prepared by the co‐precipitation method, followed by impregnation of Pd metal precursors. The physicochemical properties of the catalytic system are investigated using various techniques such as Brunauer‐Emmett‐Teller (BET), X‐ray Diffraction (XRD), X‐ray photoelectron spectroscopy, Transmission Electron Microscopy (TEM), Raman spectroscopy, and H2‐TPR. Among all, Pd/CeO2−MgO (3 : 1) gave the best NOx reduction activity. Furthermore, the effects of hydrogen concentration (0.2–0.8 vol %) on NOx reduction were tested. It was found that 0.8 vol % of H2 shows the highest NOx conversion. Subsequently, the successive impregnation of Pt metal over Pd based catalyst enhanced the catalytic properties. The bimetallic Pt−Pd/CeO2−MgO (3 : 1) catalyst showed an 89 % NOx reduction with about 97 % N2 selectivity in broad temperature windows (100–300 °C).

Unraveling the origin of extraordinary lean NOx reduction by CO over Ir-Ru bimetallic catalyst at low temperature

Ir-Ru/Al2O3 developed has shown an outstanding activity for reducing NOx by CO at low temperature in excess oxygen. However, it has remained elusive how the Ir-Ru catalyst derives this unique reactivity. Here, we tried to unveil the origin of the synergistic effect in the Ir-Ru catalyst on the lean deNOx by CO. Ir-Ru/Al2O3 showed superb NOx reduction activity along with high N2 selectivity compared to monometallic catalysts. Results of EXAFS and XRD studies indicated the formation of Ir-Ru alloy phases on the alumina. These alloy phases were likely to accelerate reaction steps required for the NOx reduction by CO, based on temperature programmed experiments together with DFT calculations. Ir-Ru/Al2O3 appeared to effectively dissociate NO on the bimetallic site, which could successively be reutilized by the facile CO-O reaction, believed to be the primary causes for the excellent deNOx activity of Ir-Ru/Al2O3 by CO under lean exhaust condition.

Unraveling the Unexpected Offset Effects of Cd and SO2 Deactivation over CeO2-WO3/TiO2 Catalysts for NOx Reduction.

It is challenging for selective catalytic reduction (SCR) of NOx by NH3 due to the coexistence of heavy metal and SO2 in the flue gas. A thorough probe into deactivation mechanisms is imperative but still lacking. This study unravels unexpected offset effects of Cd and SO2 deactivation over CeO2-WO3/TiO2 catalysts, potential candidates for commercial SCR catalysts. Cd- and SO2-copoisoned catalysts demonstrated higher activity for NOx reduction than a Cd-poisoned catalyst but lower than that for an SO2-poisoned catalyst. In comparison to SO2, Cd had more severe effects on acidic and redox properties, distinctly decreasing the SCR activity. After sulfation of Cd-poisoned catalysts, SO42- preferentially bonded with the surface CdO and released CeO2 active sites poisoned by CdO, thus reserving the highly active CeO2-WO3 sites and maintaining a high activity. The sulfation of Cd-poisoned catalysts also provided more strong acidic sites, and the synergistic effects between the formed cerium sulfate and CeO2 contributed to the high-temperature SCR performance. This work sheds light on the deactivation mechanism of heavy metals and SO2 over CeO2-WO3/TiO2 catalysts and provides an innovative pathway for inventing high-performance SCR catalysts, which have great resistance to heavy metals and SO2 simultaneously. This will be favorable to academic and practical applications in the future.

Precise control of post-treatment significantly increases hydrothermal stability of in-situ synthesized cu-zeolites for NH3-SCR reaction

The origin of the beneficial effects of post-treatment processing with HNO3 and NH4NO3 solutions on the catalytic performance of copper-amine templated zeolites used in the NH3-SCR reaction was investigated. By careful design and optimization of the dual-treatment procedure (HNO3-NH4NO3), Cu-SSZ-13 catalysts were obtained using Cu-TEPA as a template that exhibited NOx conversion above 90% in a wide temperature window from 250 to 450 ℃ with GHSV of ∼ 400,000 h−1, even after hydrothermal aging at 750 and 800 ℃. The results of XRD and H2-TPR indicated that the HNO3 post-treatment adjusts the zeolite crystallinity and optimizes the copper species distribution in Cu-SSZ-13 catalysts. Further treatment with NH4NO3 reduces the Cu/Al ratios effectively and avoids the accumulation of Cu2+ ions to form CuOx clusters during hydrothermal aging. We investigated the influence of Cu2+ on the hydrothermal stability of Cu-SSZ-13, and two opposing effects were found. Cu2+ ions inhibit dealumination of the SSZ-13 zeolite structure, while excessive quantities of them easily accumulate to form CuOx clusters, leading to collapse of long-range order in the zeolite structure during hydrothermal aging. Before the zeolite structure collapses, Cu-SSZ-13 catalysts with high Cu loading exhibit higher NH3-SCR activity due to the preservation of more active Cu2+. However, Cu-SSZ-13 catalysts totally lose deNOx activity in NH3-SCR once the zeolite structure collapses. To guarantee both the activity for NOx reduction and hydrothermal tolerance, the optimal Cu loading (Cu/Al = 0.22∼0.31, here) and structural stability of in-situ synthesized Cu-SSZ-13 should be carefully tuned by HNO3 and NH4NO3 treatment.