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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 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]

• 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]

[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]

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]

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]

[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]