deNOx Efficiency Research Articles

Experimental study of SCR DeNOX efficiency at low exhaust gas temperatures

Experimental study of SCR DeNOX efficiency at low exhaust gas temperatures

Effect of crystalline TiO2 on V2O5WO3/TiO2 as tunable low-temperature shift De-NOx catalyst

Based on the crystalline size of anatase TiO2, a series of tunable low-temperature shift V2O5-WO3/TiO2 (VW/Ti) catalysts for NH3 selective catalytic reduction (NH3-SCR) of NOx were prepared by impregnation process. These catalysts contained a loading amount of 2 wt% WO3 and either 2 or 5 wt% V2O5. The tunable low-temperature shift De-NOx performance of the VW/Ti catalysts was significantly enhanced and dramatically decreased after heat treatment of TiO2 from 100 °C to 700 °C (Ti100 ∼ Ti700). Nearly 100 % De-NOx efficiency was achieved at a gas hourly space velocity (GHSV) of 60,000 h−1. A notable shift from higher to lower temperatures was observed from V2W2/Ti100 to V2W2/Ti600; however, the activity was lost for V2W2/Ti650 to V2W2/Ti700. When the V2O5 loading increased from 2 wt% to 5 wt%, the V5W2/Ti600 showed the highest De-NOx efficiency at 225 °C, demonstrating a remarkable synergistic effect compared to the V2W2/Ti100 catalyst, which achieved maximum efficiency at 375 °C. The De-NOx performance and low-temperature shift effect of these catalysts were elucidated by considering TiO2 crystalline size, the synergistic effect between V2O5 content and TiO2, and the V4+/V5+ oxidation state of V2O5 in the catalyst. Additionally, the high crystalline TiO2-based V2W2/Ti600 catalyst prepared in this study is expected to effectively decompose NOx at low temperatures, in contrast to the low crystalline TiO2-based V2W2/Ti100 catalyst.

Magnetic field and dielectric beads modulate DBD reduced electric field with discharge homogeneity to realize NOx differential conversion

In this paper, the reduced electric field and the discharge homogeneity of DBD were modulated by the magnetic field and the packed ZrO2 beads. Subsequently, the reduced electric field and the discharge homogeneity on discharge performance, de-NOx efficiency and NOx conversion mechanism were evaluated. The experimental results show that the reduced electric field gradually enhances as the magnetic field increases, promoting de-NOx performance. The discharge homogeneity significantly weakens with the length of packed ZrO2 beads increases, inhibiting the de-NOx performance. Compared to the reactor with the packed ZrO2 beads, the de-NOx efficiency of the reactor with a 0.2 T magnetic field can achieve 87.2 %, an improvement of 39.3 %. Meanwhile, the selectivity of NO2 and N2O are reduced by 18.3 % and 21 %, respectively. The de-NOx mechanisms indicate that the reduced electric field affects the electron collision reactions and the relative rate of the NOx conversion reactions by altering the electron energy distribution. The discharge homogeneity alters the degree of plasma mitigation of exhaust gases by regulating the absolute rate of the NOx conversion reactions. The by-product N2O is mainly dependent on the concentration of NO2 and is less sensitive to N2(A3). This work reveals the differential mechanisms of reduced electric field and discharge homogeneity on de-NOx.

Boosting DeNOx performance via magnetic enhancement in synergistically-optimized γ-Fe2O3-CuO composite oxides

Fe or Cu oxides and their composites are cost-effective yet seldom used in DeNOx because they deactivate easily. Doping/supporting enhances activity but increases synthesis complexity and cost. Here, we present a γ-Fe2O3-CuO composite oxide with a high synergy created through co-oxidation, which upon magnetization, exhibits further enhanced DeNOx activity. Detailed quasi in-situ XRD and in-situ DRIFTS analyses indicate that in Fe-Cu composite oxides, iron species inhibit the full reduction of Cu2+ to Cu0, while copper counters the formation of inactive α-Fe2O3, contributing to the γ-Fe2O3-CuO composite’s enhanced stability during reactions. Fascinatingly, pre- and post-magnetization XPS and in-situ DRIFTS analyses demonstrate the magnetic field’s role in promoting the chemisorption of both oxygen and NO, thereby enhancing DeNOx efficiency. This research not only achieves the synergistic coupling of copper and iron oxides and sheds light on the deactivation processes of their pure species but also serves as a pioneering exploration of magnetic manipulation in catalyst design, laying a foundation for future technological advancements.

Exploring the limit of Cu-based small-pore zeolite framework collapse during hydrothermal aging in NOx abatement from diesel vehicle exhaust

Cu-SSZ-13 small-pore zeolites have been commercialized for NOx abatement in diesel engines, while they still suffer from hydrothermal deactivation. To identify the changes occurring in catalysts during the whole hydrothermal aging (HTA) process, the selective catalytic reduction by ammonia (NH3-SCR) performance of hydrothermally aged catalysts was investigated until total deactivation occurred. Through precisely identifying the alterations in the zeolite framework and active Cu sites during HTA, three stages were distinguished under progressively more severe HTA conditions, which were dealumination/transformation of active Cu species, CuOx accumulation, and structural collapse. These three stages were found to cause a slight decrease, serious attenuation, and total deactivation of the deNOx efficiency, which stemmed from the loss of Bronsted acid sites, reduction in the number of active Cu ion sites and structural collapse, respectively. This work also depicted simulated deactivation curves of Cu-SSZ-13 with various compositions during the HTA process, which helps in understanding the hydrothermal aging limits of catalysts with various Si/Al ratios and Cu loadings.

Enhanced DeNOx catalysis: Induction-heating-catalysis-ready 3D stable Ni supported metal combinations

Catalysis plays a critical role in the quest for sustainable automotive technology, particularly in reducing harmful emissions from vehicles. The catalysts are required to operate efficiently in dynamic and challenging environments. This study introduces innovative deNOx catalysts featuring nominal concentrations of Pd and Re nanoparticles doped on a NiMo support. The best-performing fabricated catalyst demonstrated impressive 95 % NOx conversion at 250°C, significantly outperforming traditional systems and reducing ammonia slip. Integrating nickel as the support material was strategic choice to leverage novel induction heating-assisted catalytic system. This approach is particularly advantageous when starting cold engine, reducing harmful NOx emissions when the catalyst is not fully operational. Functional monolith model of car converter catalyst with similar composition was also developed. This research presents novel catalyst solution that achieves high deNOx efficiency while offering a cost-effective alternative to traditional methods. Induction heating enhances the catalyst's performance, particularly at lower temperatures, showcasing significant improvement over conventional thermal methods.

Insight into the performance-boosting mechanism of Ag/MgAlOx for NH3 selective catalytic oxidation: Perspective from the support crystalline phase structures

Arranging an ammonia oxidation process after the selective catalytic reduction of NOx by NH3 (NH3-SCR) system is an effective way for ensuring the DeNOx efficiency and controlling the slip ammonia. To improve operability and reduce operating costs in ammonia selective catalytic oxidation (NH3-SCO), developing feasible and efficient catalysts becomes meaningful. Herein, focusing on the dilemma of Ag/Al2O3 catalysts in NH3-SCO applications, Ag/MgAlOx catalysts with different support different crystalline phase structures (5 %Ag/MgAl-LDO and 5 %Ag/MgAl2O4) were innovatively synthesized and systematically evaluated application potential in NH3-SCO. Results indicated that the introduction of Mg apparently broadened reaction temperature window and catalytic performance of 5 %Ag/MgAl2O4 was higher than 5 %Ag/MgAl-LDO, while the N2 selectivity was completely opposite. The combination of series characterization and density functional theory (DFT) calculations revealed that 5 %Ag/MgAl2O4 surface has more Ag0 species with small particle size, which is favorable for ammonia adsorption and activated dehydrogenation to further promote reaction of NOx species, resulting in a higher NH3-SCO activity. In contrast, 5 %Ag/MgAl-LDO readily induces oxidized Ag species and Ag0 is more inclined to be present in large particle sizes, which is more conducive to dissociation of O2 to produce reactive O species (O*) leading to the peroxidation of ammonia to nitrate and thus, positively affects the improvement of N2 selectivity. Model catalyst 5 %Ag/MgAl-650 (mixed-phase) was prepared by controlling the roasting conditions and exhibited excellent catalytic performance in NH3-SCO with almost 93 % of NH3 oxidized at 250 °C (N2 selectivity up to 71 %). This work could afford theoretical support for the optimization and application of catalysts with high performance at low temperatures in selective catalytic oxidation of slip ammonia.

Effect of water vapor on low temperature SCR performances over Cu and Mn-based catalysts: A comparison study

In this study, the commonly used Cu or Mn-based low-temperature SCR catalysts were employed to investigate their different reaction behaviors in the presence of high-content water vapor. Experimental results reveal that CuCeTi sample possesses superior water resistance at low temperature compared with MnCeTi catalyst. Upon the introduction of water vapor, both catalysts exhibit a quick loss in deNOx efficiency, while that is more pronounced on MnCeTi sample. In addition, unlike CuCeTi sample, MnCeTi catalyst also shows a gradual deactivation tendency after initial quick activity loss. Characterization and simulation results indicate that H2O is more easily adsorbed and dissociated on MnCeTi catalyst, showing stronger suppression on NH3 adsorption, causing more serious initial deactivation. Furthermore, more abundant hydroxyl groups derived from dissociative adsorption of water on MnCeTi catalyst will lead to more NH4NO3 deposition and the decrease in redox capacity. This is the main reason of gradual deactivation of MnCeTi catalyst at high-content water vapor. Such findings could pave a new way for development of highly efficient SCR catalysts with good water resistance for real application.

Dual-course dielectric barrier discharge with a novel hollow micro-holes electrode to efficiently mitigate NOx

The effect of a novel hollow annular micro-hole electrode on the DBD de-NOx performance was investigated. The experimental results show that the hollow electrode allows the feed gas to take full advantage of the redundant heat of the electrode, thus reducing the energy consumption of the system. Subsequently, the micro-hole structure can improve the uniformity of feed gas in the plasma channel and prolong the residence time of the feed gas in the plasma channel. The reactor can also raise the temperature of the feed gas and enhance the plasma electric field. The optimum NOx removal efficiency of about 82.6% is achieved at 16 annular micro-holes. Compared to the rod electrode reactor, the novel electrode reactor shows 19.7% reduction in energy consumption and 13.2% enhancement in de-NOx efficiency. The calculations of de-NOx mechanism show that the NO2 concentration decays significantly as the feed gas residence time increases, accompanied by a slight increase in N2O concentration. The NO2 concentration marginally increases while N2O concentration slightly decreases as the increase of feed gas temperature. DBD de-NOx presents the mode of accelerated reduction of NO, essential removal of NO2, and gradual consumption of N2O with the reduced electric field increases.

High-temperature selective reduction of NOx into N2 catalyzed by different ion-doped titania

The active titanium-based composite oxide carrier with strong thermal stability and surface acidity is the key to ensure the steady operation of high-temperature deNOx catalyst for gas-fired exhaust. In this paper, W6+, Zr4+, Mo6+, Al3+, Si4+, Cu2+, Co2+, Mn2+, Fe3+ doped titanium-based composite oxides were synthesized by sol–gel method. The effects of ion species, doping amount, calcination temperature on NH3-SCR deNOx efficiency and resistance to water vapor and SO2 poisoning were investigated. Results showed that the Cu2+, Co2+, Mn2+, Fe3+ doped titanium-based composite oxides calcined at 630 °C had negligible deNOx activity, while the doping of W6+, Zr4+, Mo6+, Al3+ and Si4+ improved the NH3-SCR activity and anti-water vapor and SO2 poisoning of titanium-based composite oxide. The deNOx efficiency of the best compatibility of the five ions doping was TiW0.1Ox-630 > TiMo0.12Ox-630 > TiAl0.11Ox-487 > TiZr0.06Ox-538 ≈ TiSi0.04Ox-582, which was consistent with the order of total acid amount. The order of resistance to water vapor and SO2 poisoning and resistance to high temperature thermal shock was TiW0.1Ox-630 ≈ TiMo0.12Ox-630 > TiSi0.04Ox-582 > TiZr0.06Ox-538 > TiAl0.11Ox-487. Doping of five ions inhibited the transformation of anatase TiO2 to rutile TiO2 in different degrees. Among them, W6+ doping had the best inhibitory effect and the exposure ratio of TiO2 (101) crystal plane in TiW0.1Ox-630 was the highest, which was beneficial to NH3-SCR of NOx. Furthermore, the concentration of chemisorbed oxygen Oα was in the order of TiW0.1Ox-630 > TiMo0.12Ox-630 > TiAl0.11Ox-487 > TiZr0.06Ox-538 > TiSi0.04Ox-582. The higher the concentration of Oα is, the more conducive to the oxidation of NO to NO2 and the promotion of NH3 adsorption and dehydrogenation oxidation.

Enhancement of low-temperature activity of γ-Fe2O3-modified V2O5-MoO3/TiO2 catalysts for selective catalytic reduction of NOx with NH3

In this study, a series of γ-Fe2O3-modified V2O5-MoO3/TiO2 (VMT) catalysts was prepared by wet impregnation method. The γ-Fe2O3-modified catalysts exhibited excellent catalytic performance, and 1.25 wt% γ-Fe2O3 content improved the deNOx efficiency at 150 °C from 54% (unmodified VMT catalyst) to 84% (modified catalyst). BET, XRD, XPS, NH3-TPD, H2-TPR, and in situ DRIFTs were employed to characterize the physicochemical properties and reaction mechanisms of the catalysts. The introduction of γ-Fe2O3 increased the V5+/V4+ ratio, surface chemisorbed oxygen content, redox ability, and a number of acid sites in the prepared catalysts. XPS confirmed the addition of γ-Fe2O3 introduced new charge transfer pathways (Fe3+/Fe2+ ↔ V5+/V4+). In situ DRIFTs suggested that the addition of γ-Fe2O3 to the catalyst significantly increased the adsorption capacity of catalyst for NH3 and NOx, while also exerting a strong activating effect on the adsorbed NH3. Furthermore, selective catalytic reduction over the VMT and 5PEG@1.25Fe-VMT catalysts followed the Eley-Rideal (E-R) mechanism. At temperatures above 200 °C, the 5PEG@1.25Fe-VMT catalyst also followed the Langmuir-Hinshelwood (L-H) mechanism.

Rational design on hierarchically porous Cu/ZSM-5 zeolite for promoting low-temperature NH3-SCR performance based on protectively alkali-etching strategy

In this study, organic structure-directing agents (OSDA) of TPA+ are used as templating agents to synthesize zeolites with different topologies, and are also served as protectants for alkali treatment to inhibit the severe silicon extraction from zeolite skeleton. The TPA+ cations could be bound to the negatively charged Al sites in the framework, so we prepared a series of Cu-based ZSM-5 catalysts with mesoporous/microporous composite structure by using TPA+ cation as a protectant for alkali treatment and evaluated the pore structures by using the hierarchy factor (HF). The results show the hierarchically mesoporous/microporous structure of the alkali-etched catalyst with the maximal HF (0.115) effectively improved the low-temperature activity on selective catalytic reduction (SCR) of NO by ammonia, achieving a complete NOx to N2 conversion at 225–400 ºC. It was shown that the TPA+ cation played an important role on protecting the crystallinity, long-range order, and pore connectivity of zeolites, and substantially widened the mesopore volume with the loss of a small portion of micropores. In addition, the alkali treatment strategy involving protectant was systematically studied, including the corresponding effect on the pore structure, redox ability, acidity, and copper ion dispersion. The N2 adsorption-desorption experiments revealed that the maximization of the HF can be obtained by adjusting the ratio of protectant to etchant (TPA+/OH-). Among them, the Cu/ZSM-5 catalyst associated with the ratio of TPA+/OH-=0.4 and the best activity has a maximum surface area of 515 m2/g, which enhances the mesopore volume (0.325 cm3/g) by approximately three times simultaneously with only a 16.9% loss of the micropore volume (0.154 cm3/g). The hierarchically porous zeolites not only enhance the diffusion of mobile hydrated copper ions and ammonia-solvated copper complexes, but also facilitate the dispersion of copper ions. This work provides a feasible strategy to rapidly enhance the low-temperature deNOx efficiency on the zeolite catalysts.

Negative effect of industrial waste residue additives (IWRA) on NOx reduction by selective non-catalytic reduction (SNCR) in cement plant: A comparison between copper slag and iron-ore slag

The rapid development of cement plants necessitates the involvement of IWRA to improve the production performance of cement, which leads to the suppression of SNCR de-NOx process. However, the specific performance and mechanism of iron-rich waste materials on SNCR remain unclear. This study specifically addresses the effects of iron-ore slag (Fe2O3) and copper slag (Fe3O4) on the SNCR de-NOx process using fixed bed reactor in a simulated precalciner atmosphere ranging from 400 to 1000 °C. The results show that iron-ore slag had a strong inhibitory effect on the SNCR de-NOx process at low-medium temperatures (400 ∼ 800 °C), whereas copper slag could promote the NOx reduction reactions under slightly excessive NH3/NO ratio (NSR) conditions (NSR = 1.3). Both types of slag exhibited a more significant restraining effect on SNCR as ammonia concentration increased. In addition, the influence of trace elements in IWRA is not significant, which proved IWRA has incomparable substitutability and better economy than traditional catalysts. Consequently, these findings offer theoretical guidance for the subsequent implementation of IWRA in actual cement production processes. Additionally, it is advisable to avoid using Fe2O3-containing IWRA and ensure that ammonia injection points are positioned in the high-temperature region (900 ∼ 1000 °C) to achieve higher de-NOx efficiency.

NOx emissions prediction in diesel engines: a deep neural network approach.

The reduction of various nitrogen oxide (NOx) emissions from diesel engines is an important environmental issue due to their negative impact on air quality and public health. Selective catalytic reduction (SCR) has emerged as an effective technology to mitigate NOx emissions, but predicting the performance of SCR systems remains a challenge due to the complex chemistry involved. In this study, we propose using DNN models to predict NOx emission reductions in SCR systems. Four types of datasets were created; each consisted of five variables as inputs. We evaluated the models using experimental data collected from a diesel engine equipped with an SCR system. Our results indicated that the deep neural network (DNN) model produces precise estimates for exhaust gas temperature, NOx concentration, and De-NOx efficiency. Moreover, inclusion of additional input features, such as engine speed and temperature, improved the prediction accuracy of the DNN model. The mean absolute error (MAE) values for these parameters were 3.1°C, 3.04ppm, and 3.65%, respectively. Furthermore, the R-squared coefficient of determination values for the estimates were 0.912, 0.983, and 0.905, respectively. Overall, this study demonstrates the potential of using DNNs to accurately predict NOx emissions from diesel engines and provides insights into the impact of input features on the performance of the model.

Enhancing simultaneous desulfurization and denitrification efficiency of cement kiln exhaust gas via co-catalytic Fenton oxidation process

Traditional Fenton reaction can hardly achieve the simultaneous desulfurization (de-SO2) and denitrification (de-NOx) for the cement kiln exhaust gas, due to the low production of free radicals as the limited Fe2+/Fe3+ cycle. Herein, an enhanced Fenton oxidation process was developed to remove SO2 and NOx efficiently, through improved Fe3+/Fe2+ conversion via the co-catalytic effect of metal sulfides and multi-metal oxysulfides. Among them, the WS2/Fe2+/H2O2 system showed the de-SO2 and de-NOx efficiency of 100% and 83.5%, respectively, and nearly no decrease in efficiency after 300 min. The highest initial de-NOx efficiency of 95.3% was achieved when Co-Mo-W-(5-4) served as co-catalyst, and the efficiency and stability were further improved after coupling NaSO3 solution absorption. Moreover, •OH was identified as the primary reactive oxygen species (ROS) for SO2 and NOx oxidation, then a reaction mechanism focusing on the reactive oxygen species (ROS) generation as well as NOx and SO2 removal was proposed based on EPR, XPS, FTIR, and Raman analysis. Thus, the results provide theoretical and technical support for developing de-SO2 and de-NOx technologies of cement kiln exhaust gas within a single process to achieve cleaner production.

Study on DeNOx of NaClO2 in simulated seawater solution enhanced by hydrodynamic cavitation

Ship exhaust causes significant air pollution, and NOx is one of the most challenging pollutants to remove. In this study, we propose a novel method for denitrification (DeNOx) using NaClO2-simulated seawater solution enhanced by hydrodynamic cavitation. We investigate the impact of initial solution pH, temperature, NaClO2 concentration, and the inlet pressure of the hydrodynamic cavitation reactor on DeNOx efficiency. The results indicate that under optimal conditions, a 100 % DeNOx efficiency can be achieved with a NaClO2 concentration of 0.1 mmol/L. Cavitation enhances mass transfer by generating microjets and increasing the gas–liquid contact area. The oxidation of NO and NO2 by hydroxyl radicals and chlorine oxygen radicals produced through cavitation could potentially enhance NOx removal efficiency. The presence of dissolved salts in simulated seawater might boost cavitation activity by reducing vapour pressure and increasing interfacial tension, leading to the more robust collapse of cavitation bubbles and thereby reinforcing cavitation effects. In addition, the multiple reactive inorganic chlorinated radicals (Cl, HClO / ClOH·-, Cl2·-) formed in simulated seawater due to the presence of Cl- might also play an essential role in DeNOx. This study demonstrated that the DeNOx by NaClO2 in simulated seawater enhanced by hydrodynamic cavitation was a promising option for NOx removal, especially for ocean-going vessels.

Effect and optimization of radial non-uniform porosity catalyst on SCR characteristics based on response surface method

Selective catalytic reduction (SCR) system is used to the denitration (de-NOx) of diesel engine exhaust after treatment. In this work, a three-dimensional SCR model with radial non-uniform distribution of catalysts is established to study the pressure drop and de-NOx performance. Firstly, the SCR converter model with uniform catalyst distribution is selected to verify its reliability. Then, the radius R1 and porosity ԑ1 of area 1, radius R2 and porosity ԑ2 of area 2 are selected as single factor variables to study the influence on the SCR system performance. Finally, response surface methodology (RSM) is employed to evaluate and optimize the above single factor parameters affecting de-NOx performance and pressure drop of SCR system. The results showed that the change of ԑ2 had the greatest impact on de-NOx efficiency and pressure drop. The optimum condition for maximum de-NOx efficiency was estimated at the R1 of 50 mm, R2 of 100 mm, porosity ԑ1 of 0.47 and porosity ԑ2 of 0.7. Under these conditions, the de-NOx efficiency by numerical simulation was 80.37 %, which was close to the predicted value (80.68 %), and the pressure drop was 218 Pa, which was close to the predicted value (246 Pa). Compared with the uniform distribution of catalysts, the de-NOx efficiency of the optimal Case of numerical simulation is increased by 3.74 %, and the pressure drop is reduced by 46 Pa. The research can provide theoretical and engineering references for the improvement of SCR catalyst coating process.

Understanding of low- and high-temperature DeNOx efficiency for NH3-SCR via comparison on Cu modified CHA and AFX zeolites

Pursuing simultaneously with excellent low- and high-temperature (wide operation temperature window) NOx reduction efficiency (LT-/HT-NRE) is greatly appealing for the NH3-SCR applications. We herein reveal the determinant of operation temperature window by comparison of Cu-SSZ-13(CHA) and Cu-SSZ-16(AFX) catalysts. And the outstanding HT-NRE performance is obtained over the Cu0.091-SSZ-164.2 (NOx conversion > 95% up to 670 °C), which makes this catalyst has great potential for applications for HT deNOx. The combined experimental (in-situ DRIFTS) and theoretical studies [DFT, ab initio molecular dynamics &ab initio thermodynamics (AIMD/AIT)] shed deeper mechanistic insights: i) the stronger resistance of Cu speciation ([CuOH]+ → CuOx) and lower HT NH3-overoxidation activity caused by the weak thermodynamic stability of the adsorbed NH3 over Cu active site constitute two major factors leading to the superior HT-NRE of Cu0.091-SSZ-164.2; ii) while the limited internal diffusions of [Cu(NH3)2] to generate the key intermediate of [(NH3)2Cu-O2-Cu(NH3)2] causes its slightly lower LT-NRE than that of Cu0.101-SSZ-135.1. Generally, present work clarifies the NRE performance of Cu-SSZ-16 at both LT and HT, which would progress highly-efficient catalyst development.

Insights into palladium poisoning of Cu/SSZ-13 selective catalytic reduction catalysts

The impacts of Pd poisoning to the activity, selectivity, and hydrothermal stability of Cu/SSZ-13 selective catalytic reduction (SCR) catalysts are reported. Pd lowers DeNOx efficiency of Cu/SSZ-13 via two mechanisms: (1) displacing SCR active sites in the form of isolated Pd-ions, and (2) catalyzing non-selective NH3 oxidation in the form of PdO. The first mechanism works by the diffusion of isolated Pd-ions into chabazite cages to displace ZCuIIOH SCR active species, and it occurs on Cu/SSZ-13 catalysts with and without external surface CuO clusters in similar fashion. In contrast, the second mechanism works differently with and without external surface CuO clusters. For Cu/SSZ-13 catalyst without external CuO clusters (i.e., primarily isolated Cu-ions), PdO leads to significant decrease of DeNOx efficiency at reaction temperatures above ∼400 °C due to its non-selective NH3 oxidation activity at high temperatures. However, this poisoning effect becomes much less impactful on Cu/SSZ-13 catalyst containing CuO clusters. This is due to the formation of CuO-PdO solid solution via interactions between CuO and PdO, which reduces non-selective NH3 oxidation potential. Furthermore, this solid solution formation even mitigates adverse effects caused by hydrothermal aging. Hence, the poisoning effects of Pd are closely related to Cu speciation and spatial distribution of a Cu/SSZ-13 catalyst. Finally, this study suggests a strategy in eliminating Pd poisoning, that is, the introduction of an oxide phase that effectively traps PdO but does not adversely influence SCR.

Characteristics of deactivation and thermal regeneration of Nb-doped V2O5–WO3/TiO2 catalyst for NH3–SCR reaction

This study investigated the effect of Nb doping into V2O5–WO3/TiO2 (VWT) catalyst for removing NOxvia the SCR (selective catalytic reduction) by NH3. The experimental results exhibited that Nb can improve the reactivity of the VWT catalyst at low temperatures. The addition of Nb also enhanced the tolerance to SO2 and H2O. The de-NOx efficiency of the V2O5–WO3–Nb2O5/TiO2 (VWNbT) catalyst was increased up to 12% over that of the VWT catalyst at 240 °C when the catalyst was poisoned for 24 h. The prepared catalysts were characterized by FT−IR, XRD, XPS, and N2 physisorption, elemental analysis. The results showed that the ammonium bisulfate (ABS) was less formed in the VWNbT than in the VWT. Moreover, evolved gas analysis was performed to examine the thermal decomposition behavior of the poisoned catalyst, and confirmed that the ABS deposited on the catalyst was sufficiently decomposed between about 300 and 400 °C. In particular, to most effectively recover the characteristics and activity of the catalysts, thermal treatment at a temperature of 400 °C is suitable.