Search

Some fly ash components such as K could seriously weaken the catalytic performance of SCR catalyst. In this study, the core-shell-structured MnFeOx@TiO 2 catalyst is synthesized by dipping deposition method and used for the NH 3 -SCR reaction. The results show that MnFeOx@TiO 2 catalyst exhibits higher K resistance than MnFeOx/TiO 2 catalyst prepared by impregnation method. And the correlativity between the core-shell morphology and K resistance of MnFeOx@TiO 2 catalyst is studied by TEM, N 2 adsorption, XRD, XPS, TPR, TPD and in situ DRIFT. It can be found that the shell of TiO 2 has a protective effect on the active species in MnFeOx@TiO 2 catalyst. And the core-shell structure of MnFeOx@TiO 2 catalyst can produce more Mn4+ and chemisorbed oxygen species on its surface, improving reducibility and surface acidity. Moreover, the core-shell structure of MnFeOx@TiO 2 catalyst is beneficial to the adsorption of NH 3 and the formation of NO 2 , resulting in the favored SCR reaction via the Eley−Rideal and the Langmuir−Hinshelwood routes. Therefore, MnFeOx@TiO 2 catalyst shows excellent K tolerance. Image 1 • The core-shell structure of MnFeOx@TiO 2 catalyst could protect the active species from the contact with K species. • The morphology of MnFeOx@TiO 2 catalyst is propitious to the conversion from to NO 2. • The SCR process over MnFeOx@TiO 2 catalyst was advanced via both E-R and L-H modes. [ABSTRACT FROM AUTHOR]

In present study, the poisoning mechanism of Cl on V/TiO 2 catalyst for SCR removal of NOx using NH 3 as the reductant was explored by in situ DRIFT technique. The experimental results revealed that the existence of Cl did not change the SCR reaction mechanism over V/TiO 2 catalyst, which was mainly under the control of both E-R and L-H mechanisms. The deactivation of V/TiO 2 catalyst by Cl was mainly resulted from the inhibited adsorption of NH 3 and NOx species, accompanied by the decrease of the reactivity of adsorbed NH 3 species. Image 1 • The addition of Cl on V/TiO 2 catalyst has an inhibition effect on the adsorption of NH 3 and NOx species. • The reactivity of adsorbed NH 3 species over V/TiO 2 catalyst would decrease after the loading of Cl. • The addition of Cl on V/TiO 2 catalyst does not change the mechanism of NH 3 -SCR reaction over it. [ABSTRACT FROM AUTHOR]

Ca salts in fly ash have a deactivation effect on SCR catalyst. In this study, the deactivation mechanism of Ca on Ce/TiO 2 catalyst was investigated in term of the in situ DRIFT study. The experimental results indicate that the poisoning effect increases with reaction temperature. From the results of in situ DRIFT study, it may be concluded that the NH 3 -SCR reaction over Ce/TiO 2 catalyst takes place though two pathways: the L -H mechanisms (<200 °C) and the E-R mechanism (>200 °C). For Ce/TiO 2 -Ca, the NH 3 -SCR reaction over it is mainly controlled by L -H mechanism. The deactivation of Ce/TiO 2 -Ca lies in the following two aspects: (1) the inhibited NH 3 adsorption and NO oxidation (<200 °C); (2) the greatly suppressed NH 3 adsorption and activation (>200 °C). [ABSTRACT FROM AUTHOR]

Heavy metals such as Zn have a poisoning effect on the catalyst for selective catalytic reduction of NO x with NH 3 . In this study, it was found that the modification of Mn/TiO 2 catalyst with Al 2 (SO 4 ) 3 could effectively enhance its Zn resistance. From the results of characterizations including XRD, H 2 -TPR, NH 3 -TPD and XPS, it could be concluded that the lower crystallinity, the higher reducibility, the generation of more acid sites, and the presence of more Mn 4+ and chemisorbed oxygen should mainly contribute to the good Zn resistance of Al 2 (SO 4 ) 3 -modified Mn/TiO 2 catalyst. The results of in situ DRIFT study indicated that the addition of Al 2 (SO 4 ) 3 did not change the mechanism of NH 3 -SCR reaction over Mn/TiO 2 catalyst, which was under the control of both Eley–Rideal and Langmuir–Hinshelwood mechanisms. [ABSTRACT FROM AUTHOR]

Sb was used as the additive to enhance the NH 3 -SCR performance of MnTiO x catalyst. Experimental results revealed that MnSbTiO x -0.2 demonstrated outstanding NH 3 -SCR activity in a wide temperature window (100–400 ℃) and high resistance to SO 2 . Characterization results indicated the introduction of Sb into MnTiO x catalyst could improve the dispersity of active species and generate more surface acid sites, Mn 4+ and surface adsorbed oxygen species. In situ DRIFT spectra proved that the presence of Sb in MnSbTiO x -0.2 catalyst could form new Brønsted acid sites, along with the increased surface Lewis acidity. The improved adsorption of NH 3 and NO x species over MnSbTiO x -0.2 catalyst had a stimulating effect on the NH 3 -SCR reaction over it through Langmuir−Hinshelwood (L-H) route. Moreover, Sb species in MnSbTiO x -0.2 could improve the reactivities of ad-NH 3 and ad-NO x species in SCR reaction. All these factors contributed to the excellent performance of MnSbTiO x -0.2 catalyst. [ABSTRACT FROM AUTHOR]

The deactivation mechanism of alkali metals on the SCR catalyst of Ce/TiO 2 was investigated by TPD and DRIFT studies. It could be found that the addition of Na or K on Ce/TiO 2 catalyst would restrict the adsorption of NH 3, accompanied by the generation of new sites for the adsorption of NO x species. But the new-absorbed NO x species were not active in the NH 3 -SCR reaction. The results of in situ DRIFT study indicated that the addition of Na and K did not change the SCR reaction mechanism, which was the combination of the Eley–Rideal and the Langmuir–Hinshelwood mechanisms. [ABSTRACT FROM AUTHOR]

The poisoning mechanism of Cl on Ce/TiO 2 catalyst was investigated based on temperature programmed desorption (TPD) and the in situ diffuse reflectance infrared transform spectroscopy (DRIFT) studies. The results of NH 3 -TPD and NO-TPD indicated that the addition of Cl on Ce/TiO 2 catalyst would inhibit the adsorption of NH 3 species and NOx species on it. As can be seen from the results of in situ DRIFT study, the NH 3 -SCR reaction over Ce/TiO 2 and Ce/TiO 2 -Cl were all followed both the Eley-Rideal mechanism and the Langmuir-Hinshelwood mechanism. And the decreased adsorption ability of NH 3 species and NOx species on the surface of Ce/TiO 2 -Cl should be mainly responsible for its low SCR activity. [ABSTRACT FROM AUTHOR]

Na has a serious deactivation effect on Mn/TiO 2 catalyst for selective catalytic reduction of NO with NH 3 . In this study, it was found that Sb had a promotion effect on the Na resistance of MnOx/TiO 2 catalyst. Then the promotion mechanism was investigated based on the characterization results of BET, XRD, H 2 -TPR, NH 3 -TPD, XPS and in situ DRIFT. The results of H 2 -TPR and NH 3 -TPD showed that the addition of Sb on MnOx/TiO 2 could enhance the redox ability and surface acidity respectively, and the results of DRIFT indicated that the addition of Sb on MnOx/TiO 2 could generate strong Lewis acid sites on the catalyst surface for NH 3 adsorption. Therefore, the doping of Sb has a promotion effect on the Na resistance of Mn/TiO 2 catalyst. [ABSTRACT FROM AUTHOR]

• The effect of components in flue gas on commercial SCR catalyst was summarized. • The mechanisms of multifactorial synergism on VWT catalysts were first clarified. • Comprehensive approach to extend the lifetime of commercial catalysts was presented. • Concepts for catalyst lifetime prediction and management were reported. NO x does great harm to the environment and human beings. The selective catalytic reduction (SCR) of NO x with NH 3 is proven to be a mature technology to eliminate NO x from the waste gas, in which V 2 O 5 -WO 3 (MoO 3)/TiO 2 is the commercialized catalyst system. Lifetime is recognized as an important parameter to evaluate the practicality of the catalyst. However, this parameter is difficult to determine because of the variable flue gas conditions. Therefore, it is necessary to understand the impacts of different components on the deNO x performance of the catalysts so that rational lifetime management methods can be adopted. This advance would be introduced in this review first. Then the synergistic effects of multi-poisons on the catalysts would be summarized and illustrated. In accordance with these studies, some modification was conducted to enhance the catalyst's anti-poisoning ability to achieve the goal of prolonging the lifetime of the catalysts. Moreover, the latest research advances in the lifetime prediction of the SCR catalysts and the relevant management systems were summarized in the following section. This paper aims to provide theoretical guidance for simulating the catalyst deactivation process under actual conditions and shows a direction for constructing catalyst lifetime management systems. [ABSTRACT FROM AUTHOR]

Sb-modified Mn/TiO 2 catalyst synthetized by sol–gel method exhibited outstanding performance in simultaneous Hg0 oxidation and NO reduction under SCR conditions at low temperature. NO removal (>90%) and Hg0 oxidation (>80%) were simultaneously obtained over MnSb/TiO 2 -0.25 catalyst in 200–300 °C with a GHSV of 54,000 h−1. Moreover, MnSb/TiO 2 -0.25 catalyst exhibited excellent tolerance to SO 2 and H 2 O. Characterization results suggested that the well-dispersed Mn, Sb and Ti species, along with the enriched Mn4+ and surface oxygen species on Mn-Sb/TiO 2 -0.25 catalyst should play a critical role in its excellent catalytic performance. The formed HgO had little inhibition effect on NO reduction over MnSb/TiO 2 -0.25 catalyst. And the coexistence of NO and O 2 has a promotion effect on Hg0 oxidation, while NH 3 exhibited an inhibition effect on oxidation of Hg0. In SCR reaction process, the Hg0 oxidation efficiency was suppressed, but this effect could be basically eliminated by using a relatively low GHSV value. Thus using MnSb/TiO 2 -0.25 for simultaneous Hg0 oxidation and NO reduction in SCR reactor may be workable in coal-burning power plants. Based on the results of experiments and characterizations, the mechanism of synchronous removal of Hg0 and NO on MnSb/TiO 2 -0.25 catalyst could be described as:Hg0(ad)+O α (O β)→HgO(ad), NO(g)+NO 2 (ad)+NH 3 (ad)→N 2 +H 2 O. Image 1 • NO removal (>90%) and Hg0 oxidation (>80%) are achieved on MnSb/TiO 2 -0.25 catalyst. • MnSb/TiO 2 -0.25 catalyst exhibits good SO 2 /H 2 O resistance. • The reaction mechanism of simultaneous removal of NO and Hg0 is proposed. [ABSTRACT FROM AUTHOR]

Abstract Removal of NO and Hg0 simultaneously was achieved on Nb-modified MnTiO x catalyst. Experimental results revealed that high NO conversion (>95%) and Hg0 oxidation (>95%) in 200–300 °C were available on Mn 0.15 Nb 0.02 TiO x catalyst with a GHSV of 108,000 h−1. The excellent catalytic performance of Mn 0.15 Nb 0.02 TiO x catalyst should be originated from its high reducibility and massive surface chemisorbed oxygen species. Moreover, the introduction of Nb into MnTiO x catalyst greatly enhanced its resistance to SO 2 and H 2 O. Neither gaseous Hg0 nor HgO formed on catalyst surface could affect the NH 3 -SCR reaction. NO had a promotion effect on Hg0 oxidation, while NH 3 was detrimental to Hg0 oxidation owing to the inhibited adsorption of Hg0 by NH 3. Under SCR reaction conditions, an inhibition impact on Hg0 oxidation could be detected, but this negative effect could be avoided by using more catalyst sample. Highlights • Over 95% NO conversion and Hg0 oxidation is available over Mn 0.15 Nb 0.02 TiO x catalyst. • The presence of Nb in Mn 0.15 Nb 0.02 TiO x catalyst could improve is resistance to SO 2 /H 2 O. • The reaction mechanism of simultaneous removal of NO and Hg0 is proposed. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • NH 3 treatment could enhance the SCR activity and stability of CeO 2 catalyst. • NH 3 treatment could promote the adsorption of reactant species on CeO 2 catalyst. • The reactivity of ad-NH 3 species on CeO 2 catalyst is improved after NH 3 treatment. Abstract In this study, NH 3 treatment of CeO 2 was found to significantly enhance its NH 3 -SCR performance. The NH 3 -treated CeO 2 was characterized by BET, XRD, TPR and XPS. The obtained results revealed the excellent SCR activity and stability of CeO 2 catalyst treated by NH 3 should be originated from the dropped crystallinity, better reducibility, along with the production of more Ce3+ and surface adsorbed oxygen. Furthermore, in situ DRIFT study has been carried out and the results indicated that the Langmuir-Hinshelwood (L-H) mechanism could be applied for explaining the SCR reaction route over CeO 2 -N. [ABSTRACT FROM AUTHOR]

Ammonia selective catalytic reduction (NH 3 -SCR) of nitrogen oxides is an effective and well-established technology for NO x removal, but current commercial denitrification catalysts based on V 2 O 5 -WO 3 /TiO 2 have some obvious disadvantages, including narrow operating temperature windows, toxicity, poor hydrothermal stability, and unsatisfied SO 2 /H 2 O tolerance. To overcome these drawbacks, it is imperative to investigate new types of highly efficient catalysts. In order to design catalysts with outstanding selectivity, activity, and anti-poisoning ability, core-shell structured materials have been widely applied in the NH 3 -SCR reaction, which exhibits numerous advantages including the large surface area, the strong synergy interaction of core-shell materials, the confinement effect, and the shielding effect from the shell layer to protect the core. This review summarizes recent developments of core-shell structured catalysts for NH 3 -SCR, including basic classification, synthesis methods, and a detailed description of the performance and mechanisms of each type of catalyst. It is hoped that the review will stimulate future developments in NH 3 -SCR technology, leading to novel catalyst designs with improved denitrification performance. [Display omitted] • Core-shell structured materials have been widely applied in the NH 3 -SCR reaction. • Core-shell structured SCR catalyst shows high catalytic activity. • Core-shell structure could protect the active components from deactivation. [ABSTRACT FROM AUTHOR]

In this work, Mo-modified Mn/TiO 2 catalysts synthetized by co-precipitation method were applied in the SCR abatement of NOx by NH 3 . Ranging from 50 to 400 °C, Mn/TiO 2 modified with Mo showed higher efficiency in SCR reaction than Mn/TiO 2 without Mo. Among Mn/TiO 2 catalysts with different Mo doping amount, MnMo/TiO 2 -0.04 catalyst showed not only the highest SCR activity but also the best N 2 selectivity. Furthermore, MnMo/TiO 2 -0.04 also exhibited stronger resistance to SO 2 poisoning compared with Mn/TiO 2 . On the basis of the characterization means including BET, XRD, H 2 -TPR, XPS and NH 3 -TPD, MnMo/TiO 2 -0.04 was characterized with the decreased crystallinity, the increased reducibility and more surface acid sites, along with the enrichment of surface adsorbed oxygen species and Mn 4+ species. Furthermore, the analysis results of in situ DRIFT study showed that Langmuir-Hinshewood (L-H) model should be employed in explaining the accelerated SCR reaction over MnMo/TiO 2 -0.04. [ABSTRACT FROM AUTHOR]

The bad resistance to SO 2 was still the primary defect of Mn/TiO 2 catalyst for selective catalytic reduction of NOx with NH 3 . To address that, a series of MnNb/TiO 2 catalyst samples with different Nb/Mn molar ratio were prepared by sol-gel method and used in NH 3 -SCR reaction. Experimental results indicated that the MnNb/TiO 2 -0.12 catalyst exhibited outstanding SCR activity and SO 2 resistance. The introduction of Nb into Mn/TiO 2 catalyst could promote the formation of more Mn 4+ and chemisorbed oxygen species on its surface, along with the generation of more NO 2 . In addition, the doping of Nb on Mn/TiO 2 catalyst could remarkably intensify its surface acidity. All these factors were conducive to improving the SCR performance of MnNb/TiO 2 -0.12 catalyst. The results of DRIFT study revealed that the NH 3 -SCR reaction over MnNb/TiO 2 -0.12 catalyst took place through both Eley–Rideal and Langmuir-Hinshelwood pathways, in which Eley–Rideal pathway was predominant. In the presence of SO 2 , it seemed that the NH 3 -SCR reaction over Mn/TiO 2 and MnNb/TiO 2 -0.12 mainly happened between adsorbed NO 2 and gaseous NH 3 (Eley–Rideal mechanism), thus the formation of more NO 2 over MnNb/TiO 2 -0.12 catalyst should mainly account for its super SO 2 tolerance. [ABSTRACT FROM AUTHOR]

Mn/TiO 2 catalyst is a promising candidate for future utilization in low-temperature NH 3 -SCR reaction, but its bad resistance to SO 2 is still a great challenge for practical application. In this study, Eu was successfully used as the additive to improve its resistance to SO 2 under SCR conditions, while the pretreatment of Mn/TiO 2 and MnEu/TiO 2 catalyst by SO 2  + O 2 had a strong deactivation effect on them. In situ DRIFT study clarified that the deactivation of Mn/TiO 2 -S (SCR + SO 2 ), Mn/TiO 2 -S (SO 2  + O 2 ) and MnEu/TiO 2 -S (SO 2 +O 2 ) were mainly originated from the inhibited adsorption of NH 3 and NOx species, as well as the formation of a large amount surface sulfate species on them, which had a strong blacking effect on the SCR reactions over the three catalysts via both E-R and L-H routes. After the addition of Eu, SCR reaction over MnEu/TiO 2 catalyst with the existence of SO 2 took place through L-H pathway, accompanied by the generation of less surface sulfate species, which brought about the excellent SO 2 tolerance of MnEu/TiO 2 catalyst under SCR conditions. [ABSTRACT FROM AUTHOR]

The deactivation of SCR catalyst caused by K species contained in the fly ash would suppress its DeNOx performance. In this study, it was manifested that the modification of Ce/TiO 2 catalyst with P could enhance its K tolerance. To understand the promotion mechanism, the fresh and poisoned catalyst samples were subjected to the characterization techniques including BET, XRD, XPS, H 2 -TPR, NH 3 -TPD and in situ DRIFT. The results elucidated that the introduction of P species could increase the reducibility of Ce species and generate more surface chemisorbed oxygen, along with the strengthened surface acidity for NH 3 adsorption. It seemed that the NH 3 -SCR reaction mechanism over Ce/TiO 2 catalyst was a combination of L-H mechanism (<200 °C) and E-R mechanism (≥200 °C). After the addition of P species, the NO oxidation over Ce/TiO 2 catalyst was also accelerated, accompanied by the broadened temperature window for the NH 3 -SCR reaction under the control of L-H mechanism. The promoted NH 3 species adsorption and the generated more NO 2 over P-Ce/TiO 2 catalyst were conducive to the NH 3 -SCR reaction through L-H pathway, which might be the primary reason for its good K resistance. [ABSTRACT FROM AUTHOR]

Heavy metals (such as Zn and Pb) have a deactivation effect on the catalyst for selective catalytic reduction of NO with NH 3 . In this study, it was found that the modification of Mn/TiO 2 catalyst by Nb could greatly enhance its Zn resistance. From the characterization results of BET, XRD, H 2 -TPR, NH 3 -TPD, it may be concluded that the introduction of Nb into Mn/TiO 2 catalyst would lead to its lower crystallinity, more acid sites and higher concentrations of Mn 4 + and surface chemisorbed oxygen. The results of in situ DRIFT study reveal that the NH 3 -SCR reactions over Mn/TiO 2 and Mn-Nb/TiO 2 all obey both the Langmuir-Hinshelwood mechanism and the Eley–Rideal mechanism, and the doping of Nb on Mn/TiO 2 catalyst could promote the adsorption of NH 3 and NOx species on it. All these features make a contribution to the high SCR activity and good Zn resistance of Mn-Nb/TiO 2 catalyst. [ABSTRACT FROM AUTHOR]

A series of Mn/TiWO x catalysts were prepared and used in NH 3 -SCR reaction for NO x emission control. The experimental results showed that the SCR activities of Mn/TiWO x catalysts are higher than that of Mn/TiO 2 catalyst. After that, several characterization techniques including XRD, H 2 -TPR, NH 3 -TPD, XPS were used to investigate the effect of TiWO x support on the SCR performance of Mn/TiWO x (1:1) catalyst. The stronger reducibility and NH 3 adsorption capacity, and more surface chemisorbed oxygen of Mn/TiWO x (1:1) should all contribute to its better SCR performance. Moreover, Mn/TiWO x (1:1) catalyst shows higher N 2 selectivity, better SO 2 tolerance and stability than Mn/TiO 2 catalyst. The results of in situ DRIFT study revealed that the NH 3 -SCR reactions over Mn/TiO 2 and Mn/TiWO x (1:1) were all followed the Langmuir–Hinshelwood mechanism, in which the SCR reaction takes place between the adsorbed NH 3 species and NO x species. [ABSTRACT FROM AUTHOR]

The effect of HF treatment on the performance of ceria for selective catalytic reduction of NO with NH 3 was investigated in this study. The experimental results showed that HF treatment could greatly enhance the SCR performance of ceria within the temperature range of 100–400 °C. From the characterization results of Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), temperature programmed reduction of hydrogen (H 2 -TPR), temperature programmed desorption of ammonia (NH 3 -TPD) and X-ray photoelectron spectroscopy (XPS), the good performance of HF-treated ceria may be attributed to its lower crystallinity, better reducibility, higher NH 3 adsorption capacity, and the enrichment of surface chemisorbed oxygen. And the results of in situ DRIFT study indicate that the NH 3 -SCR reactions on CeO 2 and CeO 2 -F mainly follow the Eley–Rideal mechanism. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ce doping could improve the SCR activity effectively for Cu-SSZ-13 catalyst. • The highly active Cu2+ sites might be protected and the catalytic activity could be restored after the addition of Ce. • More ad-NH 3 and ad-NO x species with higher reactivity are available on Ce-Cu-SSZ-13 catalyst. Potassium has a deactivation effect on Cu-SSZ-13 catalyst for selective catalytic reduction of NO with NH 3 (NH 3 -SCR). It was demonstrated that the modification of Cu-SSZ-13 catalysts by Ce could improve its K resistance. The characterization of NH 3 -TPD and H 2 -TPR suggested that the introduction of Ce on Cu-SSZ-13 could improve its surface acidity and redox ability. Moreover, the content of Cu2+ and chemisorbed oxygen were markedly restored under the situation that Ce and K elements were coexistent on catalyst surface. The synergetic effect between Ce and Cu might be the major reason for the great K resistance and the excellent SCR performance. [ABSTRACT FROM AUTHOR]

• The ball-flowerlike structure of CoMnO x -BF catalyst could remarkably enhance its low-temperature SCR activity. • More ad-NH 3 and ad-NO x species with higher reactivity are available on the surface of CoMnO x -BF catalyst. • The redox cycle "Mn4+ + Co2+ ↔ Mn3+ + Co3+" greatly promotes the low-temperature SCR reaction over CoMnO x -BF catalyst. A novel ball-flowerlike catalyst (CoMnO x -BF) was developed by hydrothermal method for the selective catalytic reduction (SCR) of NO x by NH 3. Besides, a counterpart sample (CoMnO x) was prepared by coprecipitation way for comparison. The activity test results demonstrated that CoMnO x -BF catalyst exhibited admirable SCR performance and N 2 selectivity in a broad temperature range of 150–350 °C, along with an excellent resistance to SO 2 and high durability. Based on characterization experiments, it could be found that the superior surface area resulted from suppressed crystallization, the enrichment of surface labile oxygen and Mn4+, the stronger surface acidity and redox ability were all beneficial to the NH 3 -SCR performance of CoMnO x -BF catalyst. Additionally, the enhanced NO oxidation and more activated ad-reactants on catalyst surface could also conduce to the outstanding SCR activity of CoMnO x -BF at low temperature. [ABSTRACT FROM AUTHOR]