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Mn-based catalysts have attracted significant attention in the field of catalytic research, particularly in NOx catalytic reductions and CO catalytic oxidation, owing to their good catalytic activity at low temperatures. In this review, we summarize the recent progress of Mn-based catalysts for the removal of NOx and CO. The effects of crystallinity, valence states, morphology, and active component dispersion on the catalytic performance of Mn-based catalysts are thoroughly reviewed. This review delves into the reaction mechanisms of Mn-based catalysts for NOx reduction, CO oxidation, and the simultaneous removal of NOx and CO. Finally, according to the catalytic performance of Mn-based catalysts and the challenges faced, a possible perspective and direction for Mn-based catalysts for abating NOx and CO is proposed. And we expect that this review can serve as a reference for the catalytic treatment of NOx and CO in future studies and applications. [ABSTRACT FROM AUTHOR]

The effects of four distinct zinc species (ZnCl2, Zn(NO3)2, ZnSO4, and ZnCO3) on a Mn-Ce co-doped CuX (MCCX)catalyst were investigated and contrasted in the low-temperature NH3-SCR process. Aqueous solutions of ZnCl2, Zn(NO3)2, ZnSO4, and ZnCO3 were used to poison the catalysts. The catalytic activity of all catalysts was assessed, and their physicochemical properties were studied. There was a notable drop trend in catalytic activity in the low temperature range (200 °C) after zinc species poisoning on MCCX catalyst. Interestingly, ZnSO4 and ZnCO3 on MCCX catalyst had more serious effect on catalytic activity than Zn(NO3)2 and ZnCl2 from 150 °C to 225 °C, in which NO conversion of the MCCX-Zn-S and MCCX-Zn-C catalysts dropped about 20–30% below 200 °C compared with the fresh MCCX catalyst. The zeolite X structure was impacted by Zn species doping on the MCCX catalyst, and the Zn-poisoned catalysts had less acidic and lower redox ability than fresh Mn-Ce/CuX catalysts. Through the results of in situ DRIFTS spectroscopy experiments, all catalysts were governed by both Langmuir–Hinshelwood (L–H) and Eley–Rideal (E–R) mechanisms, and the possible mechanism for poisoning the Mn-Ce/CuX catalyst using various zinc species was revealed. [ABSTRACT FROM AUTHOR]

In this study, a series of zeolite-X-supported different crystal phases of MnO2 (α-MnO2, β-MnO2, γ-MnO2, and σ-MnO2) catalysts were prepared via a solid-state diffusion method and high-heat treatment method to explore their low-temperature NH3-SCR performance. All of the catalysts featured typical octahedral zeolite X structures and manganese dioxides species of various crystal types dispersed across the support surface. Throughout the entire temperature range of the reaction, γ-MnO2/X catalyst had the highest NO conversion. Additionally, β-MnO2/X, γ-MnO2/X, and σ-MnO2/X catalysts had nearly 100% of N2 selectivity, whereas the α-MnO2/X catalyst had the lowest N2 selectivity (about 90%) below 125 °C. Moreover, the γ-MnO2/X catalyst demonstrated superior acidity capacity and reduction ability compared with the other three catalysts. All the catalysts contained the essential intermediates NH2NO and NH4NO3 species, which are essential to the SCR reaction. More acid sites and nitrate species existed on the γ-MnO2/X catalyst than on the other catalysts, thereby boosting the SCR reaction. [ABSTRACT FROM AUTHOR]

The active components Mn and Fe oxides were loaded on the surface of CeO 2 catalyst with nanopolyhedrons morphology (CeO 2 -NPs) by impregnation method to improve the CeO 2 -NPs catalyst catalytic performance. The activity test results showed that the activity order of these catalysts within the temperature of 100–300 °C was Fe-Mn-Ce > Mn-Ce > Ce catalyst, and the NO conversion rate of Fe-Mn-Ce catalyst was the highest at 200 °C, which was about 98%. The performances of these catalysts were further investigated by SEM, XRD, XPS, Raman spectra, H 2 -TPR, NH 3 -TPD and in situ DRIFT. The results indicated that Fe-Mn-Ce catalyst possessed the best reducibility and surface acidity of the three catalysts. According to the XPS and Raman spectra tests, the sequences of the ratio of O α /(O α +O β) and Ce3+/(Ce3++Ce4+) were both Fe-Mn-Ce > Mn-Ce > Ce catalyst, which indicated that the Fe-Mn-Ce catalyst possessed the most oxygen vacancy and further improved the catalytic activity of the catalyst. Moreover, the Fe-Mn-Ce catalyst also exhibited the best tolerance to SO 2 of the three catalysts at 225 °C. In general, simultaneous loading of manganese and iron oxides on the CeO 2 -NPs catalyst could effectively improve the low temperature SCR performance of the catalyst. • Fe-Mn-Ce catalyst showed superior catalytic activity at low-temperature. • Fe-Mn-Ce catalyst had more oxygen vacancies. • Fe-Mn-Ce catalyst could increase the relative ratios of surface adsorbed oxygen. • Fe-Mn-Ce catalyst possessed the best reducibility and surface acidity. [ABSTRACT FROM AUTHOR]

In this study, Samarium (Sm) modification over Mn oxide biochar (BC)-based catalysts was synthesized and the activity of low-temperature selective catalytic reduction with NH 3 (LT NH 3 -SCR) of NO was measured. Varies in surface area and pore volume, structure, morphology, and surface chemistry of Sm-modified Mn/BC catalyst were investigated to analyze the effect of Sm on the physiochemical properties on catalyst. The Sm(0.2)-Mn/BC catalyst showed the highest NH 3 -SCR activity with the NO conversion of 85% at 200 °C and best N 2 selectivity in a broad temperature range of 75–250 °C. Doping with Sm species, Mn4+ + Mn3+/Mnn+ and O α /O β increased greatly, and the surface adsorbed oxygen were enhanced in Sm(0.2)-Mn/BC catalyst, which could promote the oxidation of NO, the NO conversion and N 2 selectivity. In addition, weak and medium acid increased markedly after the Sm species added on catalysts, causing more active sites for SCR reaction. The NH 3 -SCR reaction of Sm(0.2)-Mn/BC catalyst followed the L-H mechanism, and the generation of intermediate –NH 2 , NH 4 + species and the N x O y species were observed which played vital part in the LT NH 3 -SCR reaction. • Sm doping resulted in more active sites for SCR reaction. • Sm-modification could promote the oxidation of NO. • Sm-modification could increase both the De-NO x rate and the N 2 selectivity. • The NH 3 -SCR reaction followed the L-H mechanism. [ABSTRACT FROM AUTHOR]

CeO 2 nanorods (CeO 2 -NRs) catalyst was prepared and treated with ammonia (NH 3) gas and the effect of NH 3 treatment on CeO 2 nanorods catalyst was also studied for improving NH 3 -SCR of NO. And the catalysts were tested for NH 3 -SCR of NO during 100–450 °C. The results showed that NH 3 treatment could improve the De-NO efficiency of the catalyst, which increased evidently in the range of about 160–410 °C. XPS results revealed that NH 3 treatment made CeO 2 -NRs catalyst produce more Ce3+ on its surface, and thereby produced more oxygen vacancies and further promoted SCR reaction. The XRD and H 2 -TPR characterization test results indicated that CeO 2 catalyst with NH 3 treatment could destroy its crystallinity and enhance the reducibility. In addition, the in situ DRIFTS results also exhibited more activity functional groups on the surface of N–CeO 2 -NRs catalyst than that of CeO 2 -NRs catalyst. [Display omitted] • NH 3 treatment CeO 2 -NRs catalyst showed superior catalytic activity. • NH 3 treatment could increase the relative ratios of Ce3+/Ce4+ and the surface adsorbed oxygen. • NH 3 treatment CeO 2 -NRs catalyst had more oxygen vacancies. • NH 3 treatment CeO 2 -NRs catalyst showed the better reducibility. [ABSTRACT FROM AUTHOR]

In this study, the effect of different zinc salts (ZnCl2 and ZnSO4) on the deactivation of activated carbon(AC)‐based Mn−Ce catalysts and the poisoning mechanism of zinc salts on Mn−Ce/AC are comparatively studied. SEM, BET, XRD, XPS, H2‐TPR, NH3‐TPD and In‐situ DRIFT are used to characterize the physical and chemical changes of Mn−Ce/AC catalyst. The Selective Catalytic Reduction (SCR) activities of Mn−Ce/AC has a noticeable decline after loading zinc salts, and the highest NO conversion of Zn poisoning catalysts do not exceed 70 %. And the acid site is occupied by Zn2+ on the catalyst, which affects the chemical adsorption of NH3 and hinders the formation of the intermediate ‐NH2. Moreover, the decrease of Mn4+, reducibility of manganese oxide and acid sites are more serious on ZnC−Mn‐Ce/AC. Besides, loading ZnSO4 can improve the content of Ce3+ and Oβ on catalyst surface, which can mitigate the poisoning effects of ZnSO4 on Mn−Ce/AC catalyst. Hence, ZnCl2 displays a more serious poisoning effect on Mn−Ce/AC catalyst compared with ZnSO4. Then the probable mechanism model of ZnCl2 and ZnSO4 on Mn−Ce /AC catalyst is proposed and compared. [ABSTRACT FROM AUTHOR]

The anions of precipitants played a leading role in the formation of catalytic phase while the cations decided the stability of hydroxyl group and further altered the morphology of catalysts. That was why the ammonium and sodium hydroxide possessed the similar hydroxyl group and amorphous MnFe composition, they still presented the different surface structure features. The coupling behavior of active precursors under different precipitants was the root cause of internal motivation of catalytic properties. [Display omitted] • Anion and cation of precipitant served in phase transition and structure features. • Reactants activation of precipitants acted as the inherent motivation of activity. • Precipitant affected the catalyst intrinsic activity deeply by kinetic analysis. • Possible inductive mechanism model of three precipitants on catalyst was proposed. Herein, the inductive strategy of three precipitants on dual transition metal MnFeO x catalysts for low-temperature NH 3 -SCR reaction was investigated in detail. The results showed that the anions of precipitants played the leading role in the formation of catalytic phase, in which carbonate induced the transfer of Mn precursor from MnCO 3 to the ultimate Mn 2 O 3 phase while that of hydroxyl from Mn 3 O 4 to Mn 5 O 8 phase. Iron coupling would alter the original transition behavior of manganese due to an internal synergistic effect. Furthermore, the cations decided the stability of hydroxyl groups on ammonium and sodium hydroxide precipitants, leading to the difference of morphology in catalysts. The activity results suggested that MnFe-ammonium carbonate (denoted as AC) catalyst possessed the higher catalytic efficiency than other catalysts, with over 90% NO conversion achieved from 75 to 225 °C. The abundant Mn4+ and Fe3+ and strong surface acidity of MnFe-AC catalyst were in favor of the redox circle and the adsorption of NH 3. Both activation energy and TOF, relied on the amount of acid, confirmed that the precipitants had an effect on the intrinsic catalytic activity of the catalysts such as energy barrier and reaction rate. Transient reaction further revealed that both E-R and L-H mechanisms co-existed on all catalysts, while E-R mechanism contributed more during the SCR process. On this basis, the possible inductive mechanism model of three precipitants on MnFeO x catalyst was proposed. [ABSTRACT FROM AUTHOR]

• Transition metal oxides loaded on CeO 2 -NPs catalyst were synthesized. • Mn-loading CeO 2 -NPs catalyst displayed the highest NO x conversion. • Mn-Ce catalyst showed higher oxygen vacancy than Cu-Ce and Fe-Ce catalysts. • Mn-Ce catalyst had more NH 4 + at Brønsted acid site and NH 3, ads at Lewis acid site. Ceria (CeO 2) was considered as one of the most promising catalysts due to its oxygen storage capacity and redox property. However, the low activity of CeO 2 catalyst in SCR reaction limited its further application on industrial processes. Transition metal (Mn, Cu and Fe) oxides were impregnated on nanopolyhedron CeO 2 (CeO 2 -NP) catalysts to investigate the SCR performance. The Mn-CeO 2 -NP catalyst displayed the highest NO x conversion (ca. 70% conversion at 300 °C), followed by the Cu-CeO 2 -NP catalyst (ca. 65% conversion at 300 °C) and then the Fe-CeO 2 -NP catalyst (ca. 45% conversion at 300 °C). The results of H 2 -TPR showed that Mn-CeO 2 -NP and Cu-CeO 2 -NP catalysts were more efficient in reducing hydrogen at lower temperature than that of Fe-CeO 2 -NP catalysts. Based on XPS measurements, it was determined that the O α /(O α +O β) ratio was Mn-CeO 2 -NP (ca. 65%)> Fe-CeO 2 -NP (ca. 59%)> Cu-CeO 2 -NP (ca. 55%) catalyst. It was also shown by Raman spectroscopy that the Mn-CeO 2 -NP catalyst had a higher concentration of oxygen vacancies than that of the Cu-CeO 2 -NP and Fe-CeO 2 -NP catalysts. Meanwhile, more Brønsted acid sites, Lewis acid sites, nitrate and nitrites species were found in the Mn-CeO 2 -NP catalyst as seen by in situ DRIFT spectra. [Display omitted] [ABSTRACT FROM AUTHOR]

• Al 2 O 3 promoted the catalytic activity of Pb-poisoning MC/AC catalyst effectively. • Redox property and surface acidity were inherent motivation of catalytic activity. • Both E-R and L-H pathways occurred on fresh and poisoned catalysts. • Possible mechanism model of Al 2 O 3 on anti-PbCl 2 over MC/AC catalyst was proposed. Lead salts, as a heavy metal species, caused serious damage for the activity and operation lifetime of SCR catalysts. Al-decorated Mn-Ce/AC catalyst was synthesized using the impregnation method to investigate the anti-Pb poisoning ability of Al 2 O 3 on Mn-Ce/AC catalyst. The addition of Al expressed a significant promotion on activity of MC/AC catalyst in both fresh and poisoned states. XRD analysis confirmed that Al oxide confined the crystallization of active MnO 2 over the poisoned catalysts, contributing to the dispersion of components. From the morphology, Al doping increased the aggregation of PbCl 2 , which released more active sites and further restrained the negative effect of PbCl 2. More abundant of Mn4+ and surface oxygen with adding Al was in favor of the redox circle and the activation of reactants. The enhanced surface acidity and redox property served as the chemical motivations for the anti-PbCl 2 ability of catalysts. In situ DRIFTS demonstrated that all catalysts followed both E-R and L-H pathways, and the E-R played a dominant role in the reaction activity. PbCl 2 did not change the reaction pathways but made the reaction more difficult to happen. Finally, a possible mechanism model of Al 2 O 3 on PbCl 2 resistance over MC/AC catalyst was proposed. The addition of Al oxide effectivity increased the surface-active sites on the surface of AMC/AC catalyst. And the enhanced surface acidity and redox property served as the inherent chemical motivations for the anti-Pb poisoning ability of AMC/AC catalyst, leading to the difference in reactivity of the intermediates. On this basis, the reaction of PAMC/AC catalyst was stronger than that of PMC/AC catalyst in both E-R and L-H pathways. [Display omitted] [ABSTRACT FROM AUTHOR]

• Precipitant style served a vital role on catalyst phase transition and structure features. • Surface acidity induced by precipitants acted as the main motivation for activity. • E-R and L-H paths co-existed on both catalysts while the former contributed more. • Possible structure-activity model of different precipitants on catalyst was proposed. Herein, the structure-activity strategy comparison of two different precipitants on MnO x catalyst for low-temperature NH 3 -SCR was investigated in detail. XRD results confirmed that ammonium carbonate (denoted as AC) could transfer manganese precursor from MnCO 3 to Mn 2 O 3 phase with temperature from 80 to 450 °C, while ammonium hydroxide (denoted as AH) facilitated the phase transition of MnO x from Mn 3 O 4 to the final Mn 5 O 8 phase. Further morphology defined that Mn-AC catalyst possessed a peculiar spherical feature while Mn-AH catalyst presented an accumulation of abundant nano-particles. The activity results suggested that Mn-AC catalyst possessed higher activity compared with Mn-AH catalyst at lower temperature, with over 60% conversion achieved from 100 to 225 °C and the maximum NO conversion reached circa (denoted as ca.) 85% at 175 °C. In addition, Mn-AC catalyst possessed stronger surface acidity and redox properties than Mn-AH catalyst, which served as an important motivation for the difference in activity. More manganese ions with higher valence and surface oxygen favored the superior redox circle of Mn-AC catalyst. Transient reaction revealed that the catalysts followed both Eley–Rideal (E-R) and Langmuir–Hinshelwood (L-H) pathways while the L-H pathway was harder to occur than the former due to the intense NO x transformation over catalysts. On account of these analyses, the possible structure-activity strategy comparison model of (NH 4) 2 CO 3 and NH 4 OH precipitants on MnO x catalyst was proposed. The anions of precipitant played a leading role in the formation of the catalytic phase and surface morphology, in which AC induced active Mn precursor to transfer from MnCO 3 to spherical Mn 2 O 3 while AH developed the initial Mn 3 O 4 to final Mn 5 O 8 phase. The transition behavior of active precursors under different precipitants was the root cause of the internal motivation of catalytic properties. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Sm-doping strengthened NH 3 -SCR activity and SO 2 tolerance over MnFeO x catalyst. • Enhanced NO 2 cooperated with increased NH 3 (ads) to cause "Fast SCR" reaction. • Sm induced Fe serving as sacrificial sites to preferentially react with SO 2. • Mechanism model for improving activity and SO 2 tolerance with Sm was proposed. The development of catalysts with high NH 3 -SCR activity in the presence of SO 2 was urgent for non-electric industries to control NO x emission at low temperature. Herein, a series of Sm-doping MnFeO x catalysts were synthesized through a typical PEG-assisted co-precipitation method and applied for low-temperature NH 3 -SCR process. SmMnFe-0.1 catalyst significantly broadened the activation temperature window and yielded almost 100% NO conversion from 75 to 200 °C, simultaneously, the NO removal efficiency still maintained at about 90% in the presence of SO 2 and H 2 O. The characterization results confirmed that Sm could optimize the dispersity of active components and enlarge the surface area of catalyst. Furthermore, strong interaction among active ions facilitated more oxygen vacancies and accelerated NO oxidizing to NO 2 , further cooperating with abundant adsorbed NH 3 , leading to cause "Fast SCR" reaction. Both catalysts were dominated by the E-R mechanism despite MnFeO x catalyst also obeyed the L-H pathway. Particularly, the intense redox circles between Sm and Mn inhibited the electron transferring from SO 2 to Mn ions, and induced Fe species serving as sacrificial sites along with Sm to preferentially react with SO 2 , resulting in an excellent SO 2 tolerance, and the possible mechanism model was proposed. [ABSTRACT FROM AUTHOR]

To clarify the low-temperature NH 3 -SCR performance of Mn-Ce/zeolite catalysts and the specific promotion influence between Mn-Ce active components and zeolite supports, Mn-Ce/zeolite catalysts were synthesized using Mn-Ce mix oxides loading on several kinds of zeolites (ZSM-5 zeolite, Beta zeolite, X zeolite and Y zeolite) by impregnation method. The results indicated that Mn-Ce/X catalyst had high NO conversion of nearly 100% at 150 °C and the excellent SO 2 resistance at different temperature. The Mn-Ce/ZSM-5 and Mn-Ce/Beta catalysts had NO conversion of about 100% at 275 °C while the Mn-Ce/Y catalyst had the lowest NO conversion. Additionally, Mn-Ce/X catalyst had higher relative ratio of Mn4+ and Ce3+ species, more Brønsted acid sites and better reducibility than that of other three catalysts, which could promote NH 3 -SCR activity. Moreover, the Brønsted acid sites and the Lewis acid sites on Mn-Ce/X catalyst were more stable at low-temperature. Besides, the SCR reaction of Mn-Ce/ZSM-5, Mn-Ce/Beta and Mn-Ce/X catalysts mainly followed Langmuir-Hinshelwood (L-H) mechanism at lower temperature and Eley-Rideal (E-R) mechanism at higher temperature. Furthermore, Mn-Ce/X catalyst had better adsorption ability of nitrate and nitrite species as well, which could enhance NH 3 -SCR reaction process [Display omitted] • Mn-Ce/zeolite catalysts were firstly synthesized by loading Mn-Ce oxides on different zeolites. • Mn-Ce/X catalyst had the highest NO conversion and the best SO 2 resistance. • Mn-Ce/X catalyst had higher Mn4+/Ce3+, more acid sites and good reducibility. • Mn-Ce/zeolite catalysts followed L-H mechanism at lower temperature and E-R mechanism at higher temperature. [ABSTRACT FROM AUTHOR]

Zinc salts and SO 2 would cause Mn-Ce/AC catalyst poisoning, reducing the service life of the catalyst. In this study, the effects of Nb 2 O 5 on the tolerance of ZnCl 2 and SO 2 over Mn-Ce/AC catalyst were studied by the characterization results of BET, SEM, XRD, H 2 -TPR, NH 3 -TPD, TG and XPS. It indicated that doping Nb 2 O 5 could effectively enhance the SCR performance and N 2 selectivity of Zn-Mn-Ce/AC catalyst. Meanwhile, Nb 2 O 5 could significantly improve the SO 2 poisoning resistance of Zn-Mn-Ce/AC catalyst when sulfur dioxide was added into the reaction system. Nb 2 O 5 could react with SO 2 in a preferential way to restrain the sulfuration of manganese and cerium oxides on the catalyst. More importantly, Nb 2 O 5 reacted with SO 2 to form Nb sulfate and then formed a new acidic site on the Zn-Mn-Ce/AC catalyst surface, which promoted the adsorption of NH 3 and inhibited the adsorption of SO 2 , then restricted the reaction between NH 3 and SO 2 and hindered the formation of ammonium sulfate channels. [Display omitted] • Nb 2 O 5 could effectively improve the SCR activity of Zn-Mn-Ce/AC catalyst. • Nb 2 O 5 could effectively improve the N 2 selectivity of Zn-Mn-Ce/AC catalyst. • Nb 2 O 5 could improve anti-SO 2 poisoning performance of Zn-Mn-Ce/AC catalyst. • Nb 2 O 5 increased the redox ability, surface acidity, surface chemisorbed oxygen and Mn4+ content of Mn-Ce/AC catalyst. [ABSTRACT FROM AUTHOR]

Different exposed crystal surface CeO 2 catalysts (nanopolyhedrons and nanocubes) are synthesized and treated by NH 3 to investigate the effect of oxygen vacancies on improving NO oxidation for fast SCR reaction. The experiment results show that N-CeO 2 -NPs catalyst (treated by NH 3) has the most oxygen vacancies of the four catalysts, thus leading to the best oxidation activity of NO, which further promotes the fast SCR reaction. From the XPS and Raman spectra results, it indicates that the more oxygen vacancies are due to the higher concentration of Ce3+ and surface adsorbed oxygen resulting from the NH 3 treatment at high temperature. Meanwhile, the test of NO conversion to NO 2 shows that the rich oxygen vacancies promote the conversion of NO to NO 2 , in which N-CeO 2 -NPs catalyst yields more remarkable promotion of NO oxidation to NO 2 , respectively. Also, the magnitude of the variety is in accordance with that of the oxygen vacancy content and concentration of Ce3+ ions. Thus, CeO 2 with NH 3 treatment is found to significantly enhance its NH 3 -SCR performance which leads to higher NO x removal efficiency of N-CeO 2 -NPs catalyst with {111} exposed crystal surface. [Display omitted] • NH 3 treatment CeO 2 -NPs catalyst with {111} facet showed superior catalytic activity. • NH 3 treatment could increase the relative ratios of Ce3+/Ce4+ and the surface adsorbed oxygen. • NH 3 treatment CeO 2 -NPs catalyst with {111} facet had more oxygen vacancies. • Oxygen vacancies improved the NO oxidation in the surface of CeO 2 catalyst. [ABSTRACT FROM AUTHOR]

Ionic liquids (ILs) have been explored as a surface modification strategy to promote the oxygen reduction reaction (ORR) on Pt/C and their chemical structures were identified to have strong influence on the ORR activities. To better understand the roles of anion and cation of ILs on the catalytic reaction, two cations ([MTBD]+ and [bmim]+) were paired with three anions ([TFSI]−, [beti]−, and [C4F9SO3]−) to form various IL structures. By systematically varying the IL combinations and studying their effects on the electrochemical behaviors, such as electrochemical surface area and specific ORR activities, it was found that cation structure had a higher influence than anion, and the impact of the [MTBD]+ series was stronger than the [bmim]+ series. In addition to the investigation in the half-cell, studies were also extended to the membrane electrode assembly (MEA). Considerable performance enhancements were demonstrated in both the kinetic region and high current density region with the aid of IL. This work suggests that IL modification can provide a complementary approach to improve the performance of proton exchange membrane fuel cells. [ABSTRACT FROM AUTHOR]

In this study, the poisoning effect of CaO on activated carbon (AC)-based Mn-Ce catalysts was discussed. Loading CaO inhibited the catalytic activity of the catalyst and the NO conversion of the catalyst decreased from 69.5% to 38.2% at 75 °C. The amount of MnO2 in AC surface decreased in the process of loading CaO, which was detrimental to the Selective Catalytic Reduction (SCR) performance of the catalyst. The change of manganese oxide form inhibited generation rate for the chemisorption oxygen and NO2, which was the most critical reason for the decrease of catalytic activity. Besides, loaded CaO entered into the pores of the catalyst, which led to the blockage of the pores and further resulted in the decrease of the Brunauer-Emmett-Teller (BET) surface area and total pore volume. It also destroyed the oxygen-containing functional groups and acid site on the surface of AC. All of these caused the deactivation of Mn-Ce/AC catalyst after loading CaO. [ABSTRACT FROM AUTHOR]

[Display omitted] • Different crystalline phases of MnO 2 catalysts were prepared via a facile hydrothermal method. • γ-MnO 2 catalyst exhibited the highest NO conversion and CO conversion. • γ-MnO 2 catalyst possessed abundant surface adsorbed oxygen and Mn4+ species. • Reaction mechanism model of γ-MnO 2 catalyst for NH 3 -SCR and CO oxidation was proposed. It is indeed a challenging problem to simultaneously remove NO and CO from the steel sintering flue gas, in which a bifunctional catalyst has proven to be an efficient solution for removing both pollutants at low temperature. In this study, four different crystalline phases of MnO 2 (α-, β-, γ-, and δ-) catalysts were synthesized via a facile hydrothermal method, and the effects of their crystal structure, morphology, and physicochemical properties on the catalytic performance for NO reduction and CO oxidation were elucidated. The results indicated that γ-MnO 2 catalyst exhibited the best catalytic activity, achieving 90% NO removal efficiency and 82% CO conversion rate at 175 °C. Reaction kinetics confirmed that γ-MnO 2 catalyst exhibited a lower Ea for both NO reduction and CO oxidation compared to α-MnO 2 , β-MnO 2 and δ-MnO 2 catalysts. Meanwhile, the interaction of between NH 3 -SCR and CO catalytic oxidation reactions over the catalysts was also studied. Intriguingly, it was found that the presence of CO enhanced the catalytic activity of γ-MnO 2 catalyst in the NH 3 -SCR reaction. The results of NO + O 2 -TPD and in situ DRIFTS experiments revealed that CO contributed to the adsorption and oxidation of NO, thus promoting the L-H pathway over γ-MnO 2 catalyst. Finally, a possible mechanism model for simultaneous removal of NO and CO over γ-MnO 2 catalyst was proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] • CuO modified CeFe catalysts were prepared via wet impregnation method. • CuO could improve de-NO x and CO oxidation activities for CeFe catalyst. • CuO could increase surface acidity, Ce3+/(Ce3+ + Ce4+) ratio and surface adsorbed oxygen of CeFe catalyst. • Reaction mechanism model of CuO over CeFe catalyst for NH 3 -SCR and CO oxidation was proposed. Nitrogen oxides (NO x) and carbon monoxide (CO) coexisted in numerous industrial waste gases. And selective catalytic reduction of NO x with ammonia (NH 3 -SCR) and CO catalytic oxidation were considered as the effective technologies for simultaneous elimination of NO x and CO, respectively. However, an efficient bifunctional catalyst was crucial for achieving simultaneous removal of NO x and CO. Herein, we developed a series of Cu-modified CeFe catalysts for simultaneous removal of NO x and CO. The results demonstrated that 5Cu-CeFe catalyst presented the best catalytic performance, achieving approximately 81% NO x removal efficiency and nearly 99% CO conversion rate at 200 °C under a gas houely space velocity of 90,000 h−1. The XPS analysis demonstrated that copper oxides played a critical role in promoting the formation of Ce3+ and O β , thereby facilitating the NH 3 -SCR catalytic performance and CO catalytic oxidation. Moreover, the copper oxide modification of CeFe catalyst attained a trade-off between the surface acidity and redox ability, resulting in improving adsorption and activition capacity of the reactant gases. In situ DRIFTS experiments revealed that the NH 3 -SCR process primarily obeyed the Eley-Rideal (E-R) pathway over both CeFe and 5Cu-CeFe catalysts, while Langmuir-Hinshelwood (L-H) pathway hardly participated in NH 3 -SCR process. The presence of Cu+–CO species and surface lattice oxygen was crucial for CO oxidation, and both Mars-van Krevelen (M−K) and L-H pathways might be involved in the CO catalytic oxidation process over 5Cu-CeFe catalyst. [ABSTRACT FROM AUTHOR]

In this study, a series of K species or/and SO 2 poisoned Mn-Ce doped CuX (MCCX) catalysts were prepared from waste blast furnace slag (BFS), and the influence mechanism of K species or/and SO 2 poisoning on the catalysts in low-temperature NH 3 -SCR process was investigated. The results demonstrated that MCCX-KCl catalyst had poorer NO conversion than MCCX-K 2 O below 200 °C, and the co-existence of K species and SO 2 considerably inhibited NO conversion. Aggregation of the Cu active component might also be facilitated by co-poisoning with K species and SO 2. Furthermore, K species and SO 2 co-poisoned catalysts showed fewer isolated Cu2+ species and Mn4+ species than that of K-poisoned catalysts, indicating a decrease in active sites after the addition of SO 2. The co-effect of K 2 O/KCl and SO 2 species impaired the redox capacity and decreased the surface acidity than K-poisoned catalysts to a greater extent. Nevertheless, K-poisoning had little effect on the surface intermediates during SCR reaction process, and K-poisoned catalysts followed both Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanism. However, MCCX-KCl-SO 2 and MCCX-K 2 O-SO 2 catalysts contained fewer nitrate species, indicating that the co-effect of K species and SO 2 impeded the reaction between NO + O 2 species and pre-NH 3 species, thereby resulting in poor low-temperature NH 3 -SCR activity. [Display omitted] [ABSTRACT FROM AUTHOR]

• Toxicity effects of lead salt species on Mn-Ce/Cu-X catalyst were investigated. • Pb species might primarily occupy the active site of Mn and Cu species. • PbCl 2 and PbNO 3 species predominantly affected the Brønsted acid sites. • PbSO 4 and PbCO 3 species mainly impacted the adsorption of NO + O 2. For the sintering flue gas in steel industry, selective catalytic reduction (SCR) of NO x using NH 3 at low temperature in the presence of heavy metals is still a challenge. In this study, the toxicity effects of lead salt species (PbCl 2 , Pb(NO 3) 2 , PbSO 4 , PbCO 3) 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 PbCl 2 , Pb(NO 3) 2 , PbSO 4 and PbCO 3 on MCCX catalyst varied. The PbSO 4 had the most serious poisoning on MCCX catalyst, while PbCO 3 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 PbCl 2 and PbNO 3 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, PbSO 4 and PbCO 3 species mainly impacted the adsorption of NO + O 2 and the conversion of nitrites and nitrates on the catalysts. [ABSTRACT FROM AUTHOR]

• Different precipitants were used to prepare bifunctional MnO x catalysts via a co-precipitation method. • Mn-AC catalyst exhibited the highest NO conversion and CO conversion. • The presence of CO had an active influence on NO reduction over Mn-AC catalyst. • Reaction mechanism model of bifunctional MnO x catalysts for NO reduction and CO oxidation were proposed. In this work, ammonium carbonate, sodium hydroxide, and ammonium hydroxide were selected as the precipitants to prepare bifunctional MnO x catalysts via the PEG-assisted co-precipitation method. SEM analysis revealed that MnO x catalysts prepared with ammonium carbonate (AC) displayed a spherical morphology with relatively large size, whereas the catalysts synthesized with sodium hydroxide (SH) and ammonium hydroxide (AH) exhibited polyhedron shapes with smaller size. The results demonstrated that Mn-AC catalyst presented superior catalytic activity for both NO reduction and CO oxidation, achieving 89% NO conversion at 100 ºC and over 80% CO conversion at 200 ºC, outperforming Mn-SH and Mn-AH catalysts. Mn-AC catalyst possessed more abundant Mn4+ species and surface chemisorbed oxygen than Mn-AH and Mn-SH catalysts, which served as a significant motivation for the difference in catalytic activity. Additionally, Mn-AC catalyst exhibited stronger surface acidity, which facilitated the adsorption and activation of ammonia species in the NH 3 -SCR reaction. Furthermore, in situ DRIFTS experiment suggested that the pre-desorption of CO promoted the adsorption and activation of NO. On this basis, the possible mechanism model of three precipitants on bifunctional MnO x catalysts was proposed. [Display omitted] [ABSTRACT FROM AUTHOR]

CO-SCR was considered as one of the most optimum technologies for synergistic removal of nitrogen oxides and carbon monoxide from flue gas. CuCe catalyst showed excellent NO x and CO catalytic activity in the range of 250–500 °C because of its unique physicochemical property. Herein, the mechanism of CuCe catalyst in the CO-SCR reaction at different temperature was studied via in situ DRIFTS characterization. The result indicated that the adsorbed CO species could react with gaseous NO molecules over CuCe catalyst at 150 ºC, implying that the E-R mechanism was obeyed at lower temperature. Moreover, the nitrate/nitrite species and adsorbed CO species could react with each other on the surface of CuCe catalyst at 350 ºC, indicating that the L-H mechanism was followed in the CO-SCR reaction at higher temperature. This work proposed the reaction mechanism of CuCe catalyst at different temperature for NO reduction by CO, which could provide a theoretical direction for the optimization of CuCe catalyst and promote its application in industrial production. [Display omitted] • CuCe catalyst exhibited outstanding catalytic performance for NO and CO. • CuCe catalyst had highest ratio of Cu+ and excellent redox capacity. • E-R mechanism was obeyed at 150 °C, while both E-R and L-H at 350 °C. • Mechanism model of CuCe catalyst for CO-SCR reaction was proposed. [ABSTRACT FROM AUTHOR]

The study of SCR catalysts for nitrogen oxides reduction with NH 3 had recently attracted much attention. As a typical heavy metal element, Pb was prone to seriously damage the denitrification performance of SCR catalysts in flue-gas environment. This work systematically reviewed the mechanisms of Pb poisoning and anti-deactivation measures reported these years for SCR catalysts. The mechanisms of Pb poisoning were summarized from both physical and chemical aspects, including the specific surface area, redox ability and surface acidity of the catalysts, and the corresponding reaction paths of the catalysts were also considered during the SCR process. In the meantime, this paper reviewed the anti-deactivation mechanisms and measures currently used to solve the problem of lead poisoning for SCR catalysts. The main methods included adding active substances to improve the redox ability and surface acidity of the catalysts, using ions or anti-poisoning sites to preferentially bind to Pb species, or using the structural characteristics of the carriers to prevent Pb from contacting with active substances. The concrete measures included the modification of catalysts with metal oxides and solid super acids, the change of carriers' structure, and the dual effect of carriers and active materials. Finally, a prospect of lead poisoning for further research on SCR catalysts was proposed. [Display omitted] • Physical and chemical mechanisms of Pb poisoning on SCR catalyst were reviewed. • Anti-inactivation mechanisms for SCR catalyst in the presence of Pb were clarified. • Recent advances in anti-Pb measures of SCR catalysts were summarized. • Challenges for Pb poisoning catalyst in industrial application were proposed. [ABSTRACT FROM AUTHOR]

In this study, CuX zeolite supported Mn and/or Ce oxides catalysts were synthesized by combining ion exchange and impregnation methods, and the zeolite X was generated using blast furnace slag (BFS). Doping Mn-Ce oxides onto the CuX catalyst, which has excellent resistance to SO 2 +H 2 O, improved the catalyst's activity for NH 3 -SCR at lower temperature. In addition, electron transfer from Mn4+ to Ce3+ and Cu2+ was enhanced, and the concentration of isolated Cu2+ and chemisorbed oxygen species was higher in the Mn-Ce/CuX catalyst. Also, the Mn-Ce/CuX catalyst provided excellent SCR activity because of its high acid capacity, which allowed it to provide extra acid sites, and its high redox ability, which enhanced the re-oxidized and re-reduced cycles. Additionally, produced sulfates on the catalyst surface after SO 2 and H 2 O poisoning might occupy Cu2+ active sites and affect the SCR process by competing with acid sites, nitrate species and intermediates on the Mn-Ce/CuX catalyst. [Display omitted] • Mn or Ce/CuX catalysts were prepared successfully from blast furnace slag. • Effects of Cu sites and Mn-Ce addition on the properties of the catalyst were analyzed. • Relationship between the physicochemical properties and catalytic activities of the catalysts was revealed. • Mn-Ce/CuX catalyst had excellent low-temperature NH 3 -SCR activity and SO 2 or H 2 O resistance. [ABSTRACT FROM AUTHOR]

Lead salts poisoning was a great challenge for the catalysts application in selective catalytic reduction (SCR) reaction of NO x with NH 3 in stationary sources. Herein, several typical transition metal (Cu, Co and Zr) oxides modified Mn-Ce/AC catalysts were prepared by impregnation method, and the effects of Cu, Co and Zr doping on resistance PbCl 2 poisoning for the catalyst were investigated. The addition of three transition metal oxides improved the PbCl 2 resistance of Mn-Ce/AC catalyst and maintained excellent low-temperature denitrification activity of the catalyst. The lead resistance performance of the three metal oxides followed: Cu > Co > Zr oxides. The NO conversion of Cu-doping catalyst after PbCl 2 poisoning was only ca. 10% lower than that of fresh Mn-Ce/AC catalyst at 225 °C. Cu, Co and Zr doping could decrease the loss of specific surface area caused by poisoning, while Cu-doped catalyst showed lowest crystallinity of active components. Meanwhile, the contents of Mn4+ and chemisorbed oxygen in Cu-doped catalyst were higher than those in Co- or Zr-doped catalysts. Cu, Co and Zr doping improved the surface acidity and redox performance of the poisoned catalysts, with Cu-doped poisoned catalyst exhibiting nearly the same surface acidity and redox performance as the fresh Mn-Ce/AC catalyst. Furthermore, Cu doping could also improve NO adsorption and was in favor to the SCR process. Besides, in situ DRIFTS results showed that the catalytic reaction pathways of all the poisoned or modified catalysts were in accordance with both Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms. Finally, a possible anti-PbCl 2 poisoning mechanistic model of (Cu, Co and Zr) oxides modified on Mn-Ce/AC catalyst was proposed. [Display omitted] • Cu-modified MC/AC catalyst showed best resistance to PbCl 2 poisoning. • Transition metal oxides alleviated damage of PbCl 2 to MC/AC structure. • Redox ability and acidity of PbCl 2 -poisoned catalyst were promoted by modifying. • NH 3 -SCR reaction on PbCl 2 -poisoned catalyst followed L-H and E-R mechanism. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mn and/or Ce doping on blast furnace slag-derived zeolite X catalysts were firstly synthesized. • Mn-Ce/X catalyst had the highest NO conversion and the best N 2 selectivity. • Mn-Ce/X catalyst had higher Mn4+/Ce3+, stronger acidity and excellent redox ability. • NH 2 NO and NH 4 NO 2 intermediates on Mn-Ce/X catalyst prevented the generation of N 2 O. Several Mn and/or Ce oxides on blast furnace slag-derived (BFS-derived) zeolite X catalysts were prepared to investigate their low-temperature NH 3 -SCR performance. It was found that Mn-Ce/X catalyst had the highest NO conversion of nearly 98% at 250 °C and excellent N 2 selectivity of nearly 100% during 75–175 °C. The co-addition of Ce and Mn could inhabit the growth of crystal grains, resulting in the increase of surface area and the generation of Mn-Ce double active sites. Besides, high concentration of Mn4+ and Mn3+ could promote oxidation of NO to NO 2 accelerating the "fast-SCR" reaction and high concentration of Ce4+ could form more oxygen vacancies on Mn-Ce/X catalyst. In addition, the Mn-Ce/X catalyst had large acid amount and high redox ability owing to the co-existed Mn-Ce double active sites on zeolite catalyst and the co-effect of Mn-Ce oxides and zeolite X. Furthermore, the decomposition of NH 4 NO 3 species on Mn/X catalyst led to the low N 2 selectivity at higher temperature. While NH 2 NO and NH 4 NO 2 intermediates on Mn-Ce/X catalyst played a vital part in NH 3 -SCR reaction and prevented the generation of N 2 O, and Mn-Ce/X catalyst provided more Mn-Ce active sites for the reaction between NO 3 – species and gaseous NO, accelerating SCR catalytic reaction. [ABSTRACT FROM AUTHOR]

• Synergistic interaction of Sm and Fe enhanced Pb-resistance of Mn-Ce/AC catalyst. • Sm and Fe co-doping alleviated the damage of Pb species to catalyst structure. • Surface acidity and redox ability of Mn-Ce/AC catalyst were protected by Sm and Fe from lead. • NH 3 -SCR reaction on catalysts after Pb poisoning followed L-H and E-R mechanism. A novel anti-Pb poisoning Sm and Fe co-doped Mn-Ce/AC catalyst was prepared by impregnation method for low-temperature NH 3 -SCR of NO reaction. Maintaining the excellent low-temperature activity of Mn-Ce/AC catalyst, Sm and Fe co-doping remarkably enhanced the catalyst's Pb-resistance with NO conversion up to 77%. Sm and Fe co-doped poisoning-catalysts exhibited large specific surface area and pore volume, and the crystallinity of the MnO x and CeO x reduced. The redox properties and surface acidity of the lead poisoned SmFeMnCe/AC catalyst were effectively retained, which could promote NO oxidation and NH 3 activation, further benefiting the SCR reaction. In situ DRTFTS results indicated that the low-temperature NH 3 -SCR mechanism of all poisoned catalysts followed both L-H mechanism and E-R mechanism, and the L-H mechanism was dominated. On the one hand, the extraordinary lead resistance of Sm weakened the damage of lead species on the physicochemical properties of the catalyst; on the other hand, the high oxidation properties and surface acidity of Fe enhanced the catalytic activity of the poisoned catalyst. Finally, a possible synergistic mechanism model of Sm and Fe co-doping on Mn-Ce/AC catalyst against Pb-poisoning was proposed. [ABSTRACT FROM AUTHOR]