Selective Catalytic Reduction Performance Research Articles

Ammonia coverage ratio control of a novel two-cell SCR-DeNOX system configuration based on IA-ISMC

To respond the China’s “14th Five-Year Plan” on the control of nitrogen oxides (NOX) emission, urea-based selective catalytic reduction (SCR) system has been widely applied to reduce the NOX emission from the diesel engine. NO2 is no longer a factor to be ignored while refining the SCR-DeNOX system model because of the ship diesel engine's long-term low temperature and oxygen-rich condition, which provides abundant conditions for the creation of NO2. Therefore, a refined eight-state two-cell SCR-DeNOX model is established in this paper. Meanwhile, the trade-off between NOX emission and tailpipe ammonia (NH3) slip is one of the major challenges which SCR-DeNOX system is facing. While meeting NOX emission standards, the requirement of limiting NH3 slip to prevent secondary pollution is becoming increasingly urgent, which needs a better structure or controller. Therefore, a two-cell SCR-DeNOX system with a by-pass valve in front of the NH3 injection is designed, integral sliding mode control based on inversion algorithm (IA_ISMC) is proposed for each cell. Based on the FTP-75 test cycle, there are three points of view are presented. Firstly, compared with the traditional six-state model, simulation results from the refined eight-state SCR-DeNOX model are closer to the experimental data. Secondly, the introduction of the by-pass structure has a mild impact on the NOX conversion efficiency, but can largely limit the NH3 slip. Finally, the controller based on IA_ISMC effectively improves the tracking performance of NH3 coverage ratio and reduces the cost of NH3 injection. To sum up, the refined two-cell SCR-DeNOX system with a by-pass valve based on IA_ISMC can enhance SCR performance and lower costs.

Enhancing catalytic activity with less metal resource by regulating zeolite topology

Big-ring topology of zeolite is crucial to the catalytic activity of selective catalytic reduction (SCR) of nitrogen oxide (NOx). More works should explore how to increase the number of the big-ring topology. This work regulated ZSM-5 topologies by different acids and amino acids, exchanged Cu species into the regulated zeolites, and compared their SCR performances. L-aspartate- and L-cysteine-regulated ZSM-5 removed 67 ∼ 73 % of NO (1000 ppm, 15,000 h−1) at 150 °C. Their Cu contents were only 0.04 wt%. Under the same catalytic conditions, citric acid-regulated ZSM-5 only reached a conversion of 19 % with a Cu content of 0.15 wt%. After detailed characterizations, primary 10-membered ring (MR) on (200) plane of ZSM-5 was retained after mild treatment of the amino acids. At the same time, 5-MR on (351) and (352) planes were opened to form more 10-MR. 10-MR along (501) plane was reinforced. As a result, the 10-MR content was increased from 22 % (citric acid) to 32 % (L-aspartate and L-cysteine). The 10-MR-localized Cu was more effective than other species. Above results are in favor of understanding topology-activity relationship in zeolite. Synthesizing a more effective catalyst with less active metal is also helpful to resource saving.

Investigation of the Promotional Effect of W Modification on Selective Catalytic Reduction Performance of Ce0.4ZrOx Catalysts

Investigation of the Promotional Effect of W Modification on Selective Catalytic Reduction Performance of Ce_0.4ZrO_<i>x</i> Catalysts

Cu induced reconstruction of microporous structure of tungstophosphoric acid decorated popcarbon and the synergistic effects on NH3-SCR performance

With the common biomass niblet utilized as the green precursor and tungstophosphoric acid (TPA) as the promoter, a novel popcarbon/TPA/CuOx hybrid catalyst was initially synthesized via an economical and rapid route. A series of characterization including high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction by H2 (H2-TPR), Fourier transform infrared spectroscopy (FTIR) and Raman were carried out. The morphology characterization manifested the microporous structure with beehive-like macropores. The abundant oxygenic functional groups provided plenty of anchoring sites to the introduced ingredients (TPA polyanions and copper species) to achieve a fine disperse of active sites, which was beneficial to adsorption and activation of the reactants. The catalyst presented excellent de-NOx performance up to 95% in the whole temperature regime from 100 to 350 °C, as revealed by activity tests of selective catalytic reduction (SCR). The synergistic interactions among carbon atoms, TPA anions, and isolated copper species at different valence states greatly strengthen the electron transfer effects, which should be responsible for the low activation energy of 25 kJ mol−1 and enhanced SCR performance at low temperatures.

Modulating the acidity and reducibility of FeMn/TiO2 to boost the low-temperature selective catalytic reduction of NOx

The design and fabrication of selective catalytic reduction (SCR) catalyst with ultra-low-temperature activity is diligent, however, remains challenging hitherto. Herein, a variety of TiO2-based catalysts with various Fe/Mn ratios were fabricated using a coprecipitation technique and tested for SCR of NOx with ammonia. The experimental results demonstrate that the Fe/Mn ratio considerably affects the acidity, redox property and thereafter the NH3-SCR behavior of FeMn/TiO2 catalysts. Therein, Fe0.3Mn0.7/TiO2 exhibits the broadest activity temperature window from 75 to 210 °C because of its more reactive oxygen species and higher Mn4+ ratio on the catalyst surface, leading to improved oxidation performance and surface acidity, thereby promoting the generation of active NO2 and HONO intermediates, and thereafter enabling the catalyst to adsorb more NH3 to generate active nitrate species and increasing the NH3-SCR performance. Further increasing or decreasing the Fe/Mn ratio would downgrade the SCR performances of corresponding catalysts due to the mismatch between acidity and redox ability, which inhibits the formation of active NO2 and HONO intermediates. In-situ DRIFTS results further illustrate that the SCR of NOx over FeMn/TiO2 catalysts follow both the L-H and E-R mechanisms at the low temperature, however, the types of active nitrates flourish at high temperatures, primarily via the E-R mechanism.

Boosting NO removal performance of selective catalytic reduction with NH3 on hydrotalcite derived NiCuFe mixed oxides synthesized via urea hydrothermal method

Boosting NO removal performance of selective catalytic reduction with NH3 on hydrotalcite derived NiCuFe mixed oxides synthesized via urea hydrothermal method

Adaptive time-step unscented kalman filtering (ATS-UKF) based observer design for urea selective catalytic reduction (SCR) performance of diesel engines

To reduce the number of sensors in the SCR catalyst, state feedback and fault diagnosis information are provided. Firstly, a model based on the coupling of flow, heat transfer, and gas-solid phase catalytic reaction in the SCR system is investigated in this paper. The parabolic partial differential equations are simplified by the variable substitution method and the method of lines approach (MOL). The simplified system of equations is solved by backward differentiation formulas (BDF) with adaptive adjustment time step strategy. Meanwhile, the chemical reaction parameters are accurately calibrated per second using the Levenberg-Marquardt method. Secondly, the ATS-UKF is designed in this paper, and to ensure the synchronisation between the ATS-UKF and the SCR model calculations, the time step of solving the BDF by the SCR model is taken as the time step of propagating the sigma points. Two observation scenarios are assumed: (1) no downstream NH3 concentration sensor, ammonia coverage and downstream NH3 concentration are observed by ATS-UKF; (2) no downstream NOx sensor, ammonia coverage and downstream NOx concentration are observed by ATS-UKF. Finally, the paper carries out bench tests. In the first case, the ammonia coverage obtained by the ATS-UKF reached 0.99 with respect to the model-calculated value R². The mean absolute error (MAE) between the observed and experimental values of the ATS-UKF for the downstream NH3 concentration was 2.76 ppm. In the second case, the ammonia coverage obtained by the ATS-UKF reached 0.99 with respect to the model-calculated value R², and the MAE between the observed and experimental values of the ATS-UKF for the downstream NOx concentration was 1.53 ppm. Environmental ImplicationThe Adaptive Time-Step Unscented Kalman Filtering (ATS-UKF) enhances urea Selective Catalytic Reduction (SCR) in diesel engines, improving environmental outcomes. This method minimizes sensor dependence, enabling more precise SCR system management and effective emission reduction. By advancing emission control technologies, ATS-UKF contributes to global air pollution mitigation efforts, supporting cleaner air and environmental sustainability. Its innovative approach in monitoring and predicting SCR performance marks a significant step towards eco-friendly diesel engine operation.

Revealing different lead species of PbCl2, Pb(NO3)2, PbSO4 and PbCO3 poisoning effects on Mn-Ce/CuX catalyst for low-temperature NH3-SCR of NO

For the sintering flue gas in steel industry, selective catalytic reduction (SCR) of NOx using NH3 at low temperature in the presence of heavy metals is still a challenge. In this study, the toxicity effects of lead salt species (PbCl2, Pb(NO3)2, PbSO4, PbCO3) on Cu-exchanged zeolite X doped with Mn-Ce catalysts (MCCX) were investigated. All catalysts exhibited poor low-temperature SCR performance within 75–225 °C after Pb poisoning, and the poisoning effects of PbCl2, Pb(NO3)2, PbSO4 and PbCO3 on MCCX catalyst varied. The PbSO4 had the most serious poisoning on MCCX catalyst, while PbCO3 had poisoning effect on catalysts even at 300 °C. Lead species poisoning had bad impact on the structure of zeolite X on MCCX catalyst, and caused some agglutination of Cu species. Likewise, the Pb species might primarily occupy the active site of Mn and Cu species and influence the redox property of catalysts, thereby obstructing the redox and oxidation cycles on catalysts surface. In addition, the PbCl2 and PbNO3 species predominantly affected the Brønsted acid sites and occupied the Cu or Mn active sites, inhabiting the absorption and conversion of nitrites and nitrates on the catalyst surface. Moreover, PbSO4 and PbCO3 species mainly impacted the adsorption of NO + O2 and the conversion of nitrites and nitrates on the catalysts.

A dual-balance strategy via phosphate modification on MnO2-CeO2 for NOx and chlorobenzene synergistic catalytic control

Traditional MnO2-CeO2 (MnCe) exhibits efficient synergistic-control performance for selective catalytic reduction of NOx and chlorobenzene (CB) oxidation. However, the issues of N2O formation and chlorine-deposition remain challenges. Herein, a phosphate-modified MnCe exhibits both higher NOx and CB conversions than MnCe: N2O formation decreases by 23%, while HCl selectively increases by 10% at 300 ℃. Phosphate widens the band gap of Mn 3d of MnCe and recovers the bond length of Ce-O back to that of ceria, restricting the electrons transfer from surface cations to chlorine ions by the orbital polarization effect. Meanwhile, phosphate also provides more Brønsted and weakly Lewis acid sites, favoring CB nucleophilic substitutions rather than polychlorinated species accumulation. Both the chlorine adsorption energy and HCl formation barrier decrease after phosphate modification. This work provides a novel modulation strategy of dual-balance (reducibility vs. total acidity; Lewis vs. Brønsted) on the design of multi-pollutant control catalysts.

TiO2-coated CeCoOx-PVP catalysts derived from Prussian blue analogue for synergistic elimination of NOx and o-DCB: The coupling of redox and acidity

Achieving efficient selective catalytic reduction (SCR) of NOx and catalytic oxidation of dioxins (o-dichlorobenzene as a model) on one catalyst is still a big challenge. In order to balance the N2 selectivity of SCR and the catalytic oxidation of dioxins, the catalysts with suitable redox properties and acidity need to be designed. Herein, we synthesized Prussian blue analogue (PBA)-derived CeCoOx oxides for the simultaneous removal of NOx and o-DCB by a co-precipitation method. The crystallization rate of PBA was slowed down by the addition of Polyvinylpyrrolidone (PVP), which increased the oxides size, enhanced the crystallinity of oxides and the uniformity of the surface elements distribution. These structural effects enhanced the low-temperature redox performance of the catalysts, and thus improved o-DCB conversion and CO2 selectivity. Furthermore, the PBA structure was coated by introducing TiO2, which improved the amounts of medium-acids and the mobility of oxygen species, thus increasing the mid-and high-temperature SCR performance and N2 selectivity. In addition, the H2O resistance and stability of the catalysts were enhanced due to the protective effect of the TiO2 coating on the PBA core. The optimized CeCoOx-PVP@TiO2 catalyst exhibited stable bifunctional removal efficiencies for NOx and o-DCB, with 90% NOx conversion and 92% o-DCB conversion at 300 ℃. The possible reaction mechanisms for NH3-SCR and the catalytic oxidation of o-DCB over the CeCoOx-PVP@TiO2 catalyst were proposed based on in situ DRIFTS experiments. This work provides an efficient strategy to design advanced catalysts for the elimination of dioxins and NOx.

Boosting the low-temperature activity of fast-synthesized Cu-SAPO-18 for NH3-SCR by hydrothermal treatment

Cu-SAPO-18 catalysts attracts increasing attention in the reaction of selective catalytic reduction (SCR) of nitrogen oxides (NOx), but the catalyst synthesis process is complicated and time-consuming. Also, it is urgent to enhance the low-temperature catalytic conversion of NOx for practical applications. Herein, we reported a fast-synthesis method to prepare the Cu-SAPO-18 catalysts in 32–80 h, and the catalysts showed an excellent catalytic performance of over 80 % NO conversion at 260–480 °C. The crystalline of the catalysts was improved in short crystallization time and high crystallization temperature, accelerating the NH3-SCR reaction. The low-temperature activity of all catalysts was improved after hydrothermal treatment, and the temperature range of over 80 % NO conversion was extended to 190–515 °C for the optimized catalyst, which was due to the increasing active Cu2+ species (ZCuOH and Z2Cu, where Z represents an anionic site on the zeolite framework). The redox cycle of Cu2+/Cu+ was accelerated and more Lewis acid sites on the catalyst enhanced the NO/NH3 adsorption and activation, promoting the low-temperature catalytic activity. Furthermore, after hydrothermal treatment, part of Z2Cu species converted to ZCuOH species, which exhibited stronger NO adsorption energies (−2.06 eV) than that of Z2Cu (−1.38 eV) based on theoretical calculation. Both fresh and aged catalysts showed remarkable SO2/H2O resistance. This work reveals the effects of hydrothermal treatment on the Z2Cu and ZCuOH species, which is helpful to prepare the fast-synthesized zeolite catalysts with excellent low-temperature SCR performance.

Low-silica Cu-CHA Zeolite Enriched with Al Pairs Transcribed from Silicoaluminophosphate Seed: Synthesis and Ammonia Selective Catalytic Reduction Performance.

Cu-exchanged low-silica CHA zeolites (Si/Al ≤ 4) synthesized without organic templates are promising candidate catalysts for ammonia selective catalytic reduction of nitrogen oxides (NH3-SCR), but their practical application is restricted due to the low hydrothermal stability. Here, inspired by the transcription from duplex DNA to RNA, we synthesized Al pairs enriched low-silica CHA zeolite (CHA-SPAEI, Si/Al = 3.7) by using silicoaluminophosphate (SAPO) featured by strict alternation of -Al-O-P(Si)-O-Al-O- tetrahedra as seed. The proportion of Al pairs in CHA-SPAEI is 78%, which is much higher than that in the conventional low-silica CHA (CHA-LS, 52%). After hydrothermal ageing at 800 °C for 6 h, Cu-exchanged CHA-SPAEI shows NO conversion above 90% within 225-500 °C under a gas hourly space velocity of 200,000 h-1, which is much better than that of Cu-exchanged CHA-LS. The spatial close proximity of Al pairs in CHA-SPAEI is confirmed by the 27Al double-quantum single-quantum two-dimensional NMR analyses. The strict -P(Si)-O-Al-O-P(Si)-O- sequence in the fragments from the dissolution of SAPO seed promotes the Al pairs with the -Al-O-Si-O-Al-O- sequence via a transcription process. The utilization of aluminophosphate-based zeolites as seeds opens up a new avenue for the regulation of the Al distribution in zeolites.

Low‐silica Cu‐CHA Zeolite Enriched with Al Pairs Transcribed from Silicoaluminophosphate Seed: Synthesis and Ammonia Selective Catalytic Reduction Performance

AbstractCu‐exchanged low‐silica CHA zeolites (Si/Al≤4) synthesized without organic templates are promising candidate catalysts for ammonia selective catalytic reduction of nitrogen oxides (NH3‐SCR), but their practical application is restricted due to the low hydrothermal stability. Here, inspired by the transcription from duplex DNA to RNA, we synthesized Al pairs enriched low‐silica CHA zeolite (CHA‐SPAEI, Si/Al=3.7) by using silicoaluminophosphate (SAPO) featured by strict alternation of −Al−O−P(Si)−O−Al−O− tetrahedra as seed. The proportion of Al pairs in CHA−SPAEI is 78 %, which is much higher than that in the conventional low‐silica CHA (CHA‐LS, 52 %). After hydrothermal ageing at 800 °C for 6 h, Cu‐exchanged CHA‐SPAEI shows NO conversion above 90 % within 225–500 °C under a gas hourly space velocity of 200,000 h−1, which is much better than that of Cu‐exchanged CHA‐LS. The spatial close proximity of Al pairs in CHA‐SPAEI is confirmed by the 27Al double‐quantum single‐quantum two‐dimensional NMR analyses. The strict −P(Si)−O−Al−O−P(Si)−O‐ sequence in the fragments from the dissolution of SAPO seed promotes the Al pairs with the −Al−O−Si−O−Al−O− sequence via a transcription process. The utilization of aluminophosphate‐based zeolites as seeds opens up a new avenue for the regulation of the Al distribution in zeolites.

Unveiling the temperature-dependent effect of Zn on phosphotungstic acid-modified MnOx catalyst for selective catalytic reduction of NOx: A poison at < 180 °C or a promoter at > 180 °C

MnOx-based catalysts are highly efficient for selective catalytic reduction (SCR) of NOx with NH3 at low temperatures, but Zn contained in industrial flue gas may poison conventional SCR catalysts, and MnOx-based catalysts usually have low Zn tolerance. Herein, phosphotungstic acid-modified MnOx (denoted as Mn-HPW) was prepared to study the Zn tolerance. It was found that the deposition of Zn on Mn-HPW decreases the SCR activity at < 180 °C, but both NOx conversion and N2 selectivity are enhanced at 180–300 °C, and > 95% NOx conversion can be achieved on Zn/Mn-HPW. Relevant catalysts were characterized and the results reveal that the decline in the activity at < 180 °C is related to the decrease in the quantities of Mn4+, Mn3+, and chemisorbed oxygen as well as the decreased capacities for adsorbing and activating NH3 and NOx. The unusual improvement of SCR performance on Zn/Mn-HPW at 180–300 °C is mainly attributed to two aspects: (i) HPW can protect effectively the surface acid sites from Zn poisoning; (ii) The decrease in oxidation properties alleviates the over-oxidation of NH3, promoting the participation of more NH3 in SCR.

Cobalt-/pH-Modified V2O5-MoO3/TiO2 Catalyst with Enhanced Activity for the Low-Temperature Selective Catalytic Reduction Process

Currently, the elimination of gaseous pollutants—particularly nitrogen oxides—has emerged as a significant concern. Among various deNOx technologies, selective catalytic reduction (SCR) has gained prominence as the primary approach for NOx abatement, owing to its superior performance. In this study, novel low-temperature SCR catalysts were developed by regulating the pH value and doping cobalt based on a V2O5-MoO3/TiO2 (VMT) catalyst. The results show an increased SCR performance with 82.8% and 91.1% for catalysts after pH (=10) modification (VMT-10) and (1 wt%) Co/pH (=10) modification (1CoVMT-10), respectively. H2-TPR, NH3-TPD, XPS and DRIFTS confirmed that the pH regulation transformed polymerization V species into isolated V5+=O, thus leading to an increase in the number of acid sites, which enhanced the NH3 and NO2 adsorption capacity. Furthermore, the DRIFTS study indicated that the NH3-SCR reaction over 1CoVMT-10 followed the E–R and L–H mechanism.

Study on Diesel Engine Selective Catalytic Reduction Performance at Different Atmospheric Pressures Using the Response Surface Method.

Nitrogen oxides (NO x ) are the main emissions of diesel engines. Selective catalytic reduction (SCR) is the main technology used to reduce NO x emissions from diesel engines. NO x conversion efficiency and ammonia (NH3) escape are the main indicators to evaluate SCR performance. In this work, the effects of diesel engine exhaust temperature and exhaust mass flow rate on the SCR performance under different atmospheric pressures were studied by the combination method of experiment and one-dimensional numerical simulation. At the same time, the response surface method (RSM) was used to analyze the interaction of atmospheric pressure, exhaust temperature, and exhaust mass flow rate on the SCR performance. The results show that the lower the atmospheric pressure, the lower the NO x conversion efficiency and ammonia escape. Under the same exhaust temperature, the lower the atmospheric pressure, the smaller the impact of exhaust mass flow rate on NO x conversion efficiency. According to the RSM results, the optimal NO x conversion efficiency is 78.6% under the combination working conditions of an atmospheric pressure of 100 kPa, exhaust temperature of 395 °C, and exhaust mass flow rate of 250 kg/h, and the NH3 escape is also at a low level of 1.7 g/cycle.

Impact of Hydrothermal and Chemical Aging on SCR Storage Characteristics and NO &lt;italic&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/italic&gt; Reduction Performance in an Ultra-Low NO &lt;italic&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/italic&gt; System

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;This work is a part of medium-duty Low NO&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt; technology development project with a focus on evaluating a combination of engine and advanced aftertreatment for 0.02 g/bhp-hr NO&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt; regulation proposed by CARB (California air resource board). In this project, a control oriented chemical kinetics model of SCR (Selective catalytic reduction) was used in the aftertreatment controller that is susceptible to performance degradation due to hydrothermal and chemical aging. This paper focuses on modeling the NO&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt; conversion and NH3 storage characteristics using a controls oriented SCR plant model which is further used for a model-based urea dosing scheme. A set of steady state reactor tests were used to calibrate the SCR performance at degreened, hydrothermal only and hydrothermal + chemical aging conditions and also to determine inhibition factors related to aging. The resultant model is capable of simulating SCR performance deterioration such as a reduction in NO&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt; conversion and NH3 storage. A non-linear aging profile was observed for Lo-SCR and downstream SCR showing a change in the NO&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt; conversion in the aged system when compared to a degreened system. Upon chemical aging further deterioration of low temperature performance was observed. This aging phenomenon impacts the dosing control strategy of the system. The results on controller performance for a set of Heavy Duty Federal Test Protocol(FTP), Ramp Modal Cycle (RMC), and Low Load Cycle (LLC) are presented.&lt;/div&gt;&lt;/div&gt;

Experimental study of emission characteristics and performance of SCR coated on DPF with different catalyst washcoat loadings

To improve the NOx conversion efficiency (CE) and inlet temperature of selective catalytic reduction (SCR) under low-temperature conditions, SCR coated on diesel particulate filter, so called SDPF, is one of the important technologies to meet the future Euro Ⅶ ultra-low emission regulations for diesel engines. In this study, the effects of different Cu-SSZ-13 catalyst washcoat loadings (60, 90, and 120 g/L) on the SDPF performance were investigated. The results showed that as the catalyst washcoat loading increased, the inlet temperature and pressure drop of the SDPF rose, the high-NOx-conversion-efficiency area expanded toward the low-speed and low-load directions of the engine, and the NOx CE first increased and then decreased. The number of active sites of the catalyst and the SDPF pressure drop together determine the NOx CE. When the catalyst washcoat loading was increased, the nucleation-mode (NM) particle factor decreased significantly, while the accumulation-mode (AM) particle factor decreased slightly. The filtration efficiency of the three types of particles was NM > total > AM from high to low. The higher the washcoat loading, the higher the particle filtration efficiency and the larger the geometric mean diameter. The reduction of NM particles was the result of a combination of the chemical reaction and the physical collection mechanism.

Revealing the nature of dinuclear active sites on CenTiOx catalysts for the selective catalytic reduction NOx with NH3

A series of CenTiOx catalysts prepared by a solvothermal method was investigated on the selective catalytic reduction (SCR) of NOx with NH3. Among them, Ce0.3TiOx showed the most excellent SCR performance. Combining various characterizations with DFT calculations, it can be found that dinuclear sites, i.e., acid and redox sites, were successfully constructed on the Ce0.3TiOx surface. Specifically, pentacoordinate Ti sites served as the primary acid sites, while surface lattice O- in the adjacent Ce-O--Ce served as redox sites. Furthermore, the outstanding oxidation ability of this catalyst was crucial to active adsorbed NH3 and NHNO intermediates, which are the critical steps for the NH3-SCR reaction. Finally, a plausible NH3-SCR reaction pathway on CenTiOx catalysts was proposed.

Insight into blast furnace dust for selective catalytic reduction of NOx: An experimental and DFT study

Blast furnace dust (BFD), a solid waste generated from the ironmaking process, causes the environmental problems of soil and water pollution. In this work, we develop the selective catalytic reduction (SCR) catalyst for the nitric oxides (NO) reduction using BFD as the raw material by the co-precipitation method. To guarantee the strongest catalytic capability, different calcined temperatures are tested to activate the catalysts, where the prepared catalysts are labeled as BFD-T with the capital letter T to represent the calcination temperature. α-Fe2O3 is the main crystal phase in BFD-T catalyst and the mesoporous structure is mainly concentrated in 2–15 nm. The BFD-400 catalyst presents the best SCR performances and further increasing of the calcination temperature for the catalyst preparation reduces the reducibility, specific surface area and surface adsorbed oxygen of the catalyst. In the temperature range of 225 ℃ to 350 ℃, the BFD-400 catalyst presents the nitrogen oxides (NOx) conversion of more than 90%, which is attributed to the increase of ferric ion on the catalyst surface. Meanwhile, density functional theory (DFT) is applied to study the adsorption states of the reactant molecules on the catalyst surface and reaction mechanism. During the SCR process, this catalyst shows the excellent resistance to sulfur and water in the coal-fired flue gas due to the weak adsorption energy calculation.