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The technology of CO selective catalytic reduction of NOx (CO-SCR) showcases the potential to simultaneously eliminate CO and NOx from industrial flue gas and automobile exhaust, making it a promising denitrification method. The development of cost-effective catalysts is crucial for the widespread implementation of this technology. Transition metal catalysts are more economically viable than noble metal catalysts. Among these, Fe emerges as a prominent choice due to its abundant availability and cost-effectiveness, exhibiting excellent catalytic performance at moderate reaction temperatures. However, a significant challenge lies in achieving high catalytic activity at low temperatures, particularly in the presence of O2, SO2, and H2O, which are prevalent in specific industrial flue gas streams. This review examines the use of Fe-based catalysts in the CO-SCR reaction and elucidates their catalytic mechanism. Furthermore, it also discusses various strategies devised to enhance low-temperature conversion, taking into account factors such as crystal phase, valence states, and oxygen vacancies. Subsequently, the review outlines the challenges encountered by Fe-based catalysts and offers recommendations to improve their catalytic efficiency for use in low-temperature and oxygen-rich environments.

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Generally, sulfur poisoning is considered to be one of the main factors contributing to the deactivation of selective catalytic reduction of NOx by CO (CO-SCR) catalysts, while the promotional effect of SO2 on NO reduction over Ir/SiO2 is observed which is an interesting scientific phenomenon. After the introduction of 20 ppm SO2, NOx conversion increased from âˆ¼ 40 % to âˆ¼ 90 % at 275 °C, and N2 selectivity increased from âˆ¼ 80 % to 100 % at 200 âˆ¼ 300 °C. Furthermore, the promoting effect could remain unchanged after 24 h of continuous reaction. However, the temperature point for achieving complete conversion of CO increased from 225 °C to 275 °C after the introduction of SO2. Experimental characterization and theoretical calculation jointly proved that the inhibition of CO oxidation by the generation of sulfate was the main reason for promoting NO reduction. Under the coexistence of O2 and SO2, SO2 was firstly oxidized to SO3 on the iridium surface and generated sulfate species on surface hydroxyl groups of SiO2. Some active sites for O2 adsorption were covered by the generated surface sulfate, and adsorbed CO was hard to react with adsorbed O2, resulting in Langmuir-Hinshelwood (L-H) reaction pathways for CO oxidation being inhibited. Therefore, unoxidized CO reacted with NO adsorbed species and generated N2O to generate N2 and CO2, improving NO reduction. This new insight has implications for understanding the promotional effect of SO2 on NO reduction with CO in the presence of O2.

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We developed a simple strategy for preparing IrSn bimetallic clusters encapsulated in pure silicon zeolites via a one-pot hydrothermal synthesis by using diethylamine as a stabilizing agent. A series of investigations verified that metal species have been confined successfully in the inner of MFI zeolites. IrSn bimetallic cluster catalysts were efficient for the CO selective catalytic reduction of NOx in the presence of excess O2. Furthermore, the 13CO temperature-programmed surface reaction results demonstrated that NO2 and N2O could form when most of the CO was transformed into CO2 and that Sn modification could passivate CO oxidation on the IrSn bimetallic clusters, leading to more reductants that could be used for NOx reduction at high temperatures. Furthermore, SO2 can also influence the NOx conversion by inhibiting the oxidation of CO. This study provides a new strategy for preparing efficient environmental catalysts with a high dispersion of metal species.

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The development of efficient catalysts for the selective catalytic reduction of NO by CO (CO-SCR) in the presence of O2 is highly desirable for controlling the emission of toxic gases from tailpipes. Here, a bimetallic IrRu/ZSM-5 catalyst was prepared for the selective catalytic reduction of NO by CO in the presence of O2 (5%) for the low-temperature treatment of exhaust gas. IrRu/ZSM-5 afforded 90% NOx conversion in the range of 225-250 °C and maintained 90% NOx conversion after 12 h of reaction. Ru addition inhibited agglomeration of the Ir particles during the reduction process and provided more active sites for NO adsorption. Isotopic C13O tracing and in situ diffuse reflectance infrared Fourier-transform spectroscopy experiments were used to elucidate the CO-SCR mechanism in the absence or presence of O2. NCO could easily form on the surface of catalysts in the absence of O2, whereas NCO formation has been inhibited owing to the quick consumption of CO in the presence of O2. Moreover, some byproducts such as N2O and NO2 are generated in the presence of O2. Finally, a possible mechanism for CO-SCR under different conditions was proposed based on in situ experiments and physicochemical analyses.

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Selective catalytic reduction (SCR) is probably the most widespread process for limiting NOx emissions under lean conditions (O2 excess) and, in addition to the currently used NH3 or urea as a reducing agent, many other alternative reductants could be more promising, such as CxHy/CxHyOz, H2 and CO. Different catalysts have been used thus far for NOx abatement from mobile (automotive) and stationary (fossil fuel combustion plants) sources, however, perovskites demand considerable attention, partly due to their versatility to combine and incorporate various chemical elements in their lattice that favor deNOx catalysis. In this work, the CxHy/CxHyOz-, H2-, and CO-SCR of NOx on perovskite-based catalysts is reviewed, with particular emphasis on the role of the reducing agent nature and perovskite composition. An effort has also been made to further discuss the correlation between the physicochemical properties of the perovskite-based catalysts and their deNOx activity. Proposed kinetic models are presented as well, that delve deeper into deNOx mechanisms over perovskite-based catalysts and potentially pave the way for further improving their deNOx efficiency.

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The nature of the synergistic effect in bimetallic catalysts remains a challenging issue, due to the difficulty in understanding the adjacent interaction between dual metals at the atomic level. Herein, a CuFe-N/C catalyst featuring diatomic metal-nitrogen sites was prepared through a sequential ion exchange strategy and applied for NO selective catalytic reduction by CO (CO-SCR). The bimetallic CuFe-N/C catalyst exhibits high N2 selectivity with a NO conversion efficiency of nearly 100% over a wide temperature range from 225 to 400 °C, significantly higher than that of its single-component counterparts. The synergistic effect of bimetallic Cu-Fe sites is well revealed using the combined in situ FTIR technique and DFT calculations. Bifunctional Cu-Fe sites are demonstrated not only to provide two different preferential adsorption centers for the CO molecule and ONNO intermediate but also to achieve a complete electron cycle for efficient interfacial electron transfer upon ONNO uptake. The unique electron transfer mechanism stemmed from 4s-3d-type electron coupling, and different 3d shell fillings of Cu (3d10) and Fe (3d6) atoms are presented. These fundamental insights pave the way for the understanding of N-coordinated bimetallic site synergy and rational design of highly active atomic-scale metal catalysts for SCR applications.

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Selective catalytic reduction of NO with CO (CO-SCR) was investigated based on optimizing the operating conditions by response surface methodology (RSM) and by appropriately choosing the supported SBA-15 catalysts. The effects of the CO-SCR reaction parameters such as NO:CO molar ratios and oxygen concentrations on the catalytic performance were determined by RSM to evaluate the NO conversion using a first-order polynomial model. The CuO/SBA-15 and Fe2O3/SBA-15 catalysts were synthesized by a hydrothermal method and characterized by X-ray diffraction (XRD), atomic absorption spectroscopy (AAS), N2 adsorption-desorption (BET), scanning electron microscopy coupled to energy dispersive X-Ray spectroscopy (SEM-EDS), and Fourier transform infrared spectroscopy (FTIR) to investigate the physicochemical properties of the solids. The RSM showed a very good agreement between predicted values and experimental results with the Pareto analysis confirming the accuracy and reliability of the model. The optimized results indicated the maximum NO conversion at 500 °C with using the NO to CO molar ratio of 1:2 (500:1000 ppm) in the absence of oxygen. Under these conditions, CuO/SBA-15 catalyst achieved 99.7% of NO conversion, whereas Fe2O3/SBA-15 had 98.1% of the catalytic parameter. Catalytic tests in CO-SCR reaction were performed on both catalysts at optimum operating conditions with CuO/SBA-15 exhibiting better performance compared to that of Fe2O3/SBA-15. The results revealed that CuO/SBA-15 was a promising catalyst for CO-SCR of NO due to the well-dispersed CuO phase on SBA-15 surface that allows the solid being more tolerant to the presence of oxygen.

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Nitrogen oxide (NOx) is an important precursor for many air pollution problems such as fine particulate matter and ground-level ozone. Because air pollution levels increase daily, it is important to control NOx emissions from industrial boiler flue gas. A series of different Co3O4 catalysts was prepared in this study by different methods. The effects of the preparation methods on selective catalytic reduction of NO by CO (CO-SCR) were investigated. The catalysts were characterized by BET, XRD, HR-TEM, and Raman. The results show that the Co3O4-S catalyst, prepared by solid grinding with cobalt sulfate as the precursor, had better CO-SCR activity and H2O resistance and that Co3O4-C, prepared by solid grinding with cobalt acetate as the precursor, showed excellent H2O resistance. The NO oxidation results showed that better NO oxidation activity over the catalysts is an important reason for the improved CO-SCR activity. The Raman results indicate that more Co2+ ions appeared on the surface of Co3O4-S, which benefited the formation of oxygen vacancies. The H2-TPR results showed better redox property of the Co3O4-S catalyst. The HR-TEM results shoes that the (111) and (220) crystal planes were exposed mainly on Co3O4-S and Co3O4-O and that more (220) crystal planes are conducive to improved reaction.