Search

CuO@TiO2 core–shell nanostructure catalyst with CuO core and TiO2 shell was prepared by a two-step method and then used in NH3-SCR reaction. FE-SEM, TEM and element mapping were used to investigate the morphologies of the sample. Their results indicated CuO nanorods were coated with TiO2 and thus forming a core–shell nanostructure. According to the results of N2 adsorption–desorption, XRD, Raman, XPS, NH3-TPD, H2-TPR and in situ DRIFTS, the core–shell nanostructure would benefit the formation of better redox ability, more oxygen vacancies, more acid sites and abundant adsorbed NOx species on the catalyst. Thus, the core–shell nanostructure catalyst presented significantly higher activity than pure CuO and TiO2. NH3-SCR reaction on CuO@TiO2 core–shell catalyst should follow both Eley–Rideal (E-R) mechanism and Langmuir-Hinshewood (L–H) mechanism. These findings may promote the development of the new effective non-vanadium-based SCR catalysts. [ABSTRACT FROM AUTHOR]

Metal oxides@MOFs core‐shell materials were developed for selective catalytic reduction of NOx by NH3 (NH3‐SCR). A novel CuO@Cu‐MOFs core‐shell material with CuO as the core and Cu3(BTC)2 as the shell were rationally designed and synthesized by an in situ growth method and used in NH3‐SCR reaction. The prepared CuO@Cu‐MOFs materials combined physicochemical properties of CuO (high NO adsorption stability and excellent surface reducibility) and Cu3(BTC)2 (large specific surface area and abundant acid sites). In addition, the core‐shell materials held large amounts of Brønsted acid sites and abundant adsorbed NOx intermediate species, which benefited NH3‐SCR reaction under low‐temperature. Experimental results demonstrated that CuO@Cu‐MOFs possessed higher low‐temperature catalytic activity than that of pure CuO and Cu3(BTC)2. Importantly, CuO@Cu‐MOFs performed satisfied stability in NH3‐SCR reaction, which made it to be a potential and promising low‐temperature SCR catalyst. All grown up! CuO@Cu3(BTC)2 core‐shell materials which combined the advantages of CuO and Cu3(BTC)2 perform superb low‐temperature catalytic activity in NH3‐SCR reaction. [ABSTRACT FROM AUTHOR]

The deactivation and regeneration of selective catalytic reduction catalysts which have been used for about 37,000 h in a coal power plant are studied. The formation of Al2(SO4)3, surface deposition of K, Mg and Ca are primary reasons for the deactivation of the studied Selective catalytic reduction catalysts. Other factors such as activated V valence alteration also contribute to the deactivation. Reactivation of used catalysts via environment-friendly and finance-feasibly approaches, that is, dilute acid or alkali solution washing, would be of great interest. Three regeneration pathways were studied in the present work, and dilute nitric acid or sodium hydroxide solution could remove most of the contaminants over the catalyst surface and partly recover the catalytic performance. Notably, the acid–alkali combination washing, namely, catalysts treated by dilute sodium hydroxide and nitric acid solutions orderly, was much more effective than single washing approach in recovering the activity, and NO conversion increased from 23.6% to 89.5% at 380°C. The higher removal efficiency of contaminants, the lower dissolution of activated V, and promoting the formation of polymeric vanadate should be the main reason for recovery of the activity. [ABSTRACT FROM PUBLISHER]

Abstract: The regeneration of SCR catalyst by dilute sodium hydroxide solution was investigated. For the deactivated catalyst, the porosity disappeared and the specific surface area decreased largely, and there were impurities in deposit and variation of V valences. The dilute sodium hydroxide had a positive influence on the surface of catalysts. The porosity partly recovered and the specific surface area increased 12.75-fold, the impurities also decreased, and the amount of V4+ was partly recovered. After regeneration, the relative activity (k/k 0) at 380°C increased from 0.14 to 0.74. The alkali solution washing might be a promising approach for the regeneration of SCR catalyst. [Copyright &y& Elsevier]

[Display omitted] • CuO x /MnO 2 catalysts with different crystal phases of MnO 2 were synthesized. • CuO x / α-MnO 2 catalyst showed excellent catalytic activity in NO reduction and CO oxidation. • The presence of CO enhanced the NH 3 -SCR catalytic activity of catalyst. • Mechanism model for NO reduction and CO oxidation was proposed. NO and CO are two primary pollutants in the sintering flue gas emission, posing significant challenges for the treatment. Under oxygen-enriched conditions, CO was easily oxidized to CO 2 before participating in CO-SCR reaction as a reducing agent. Consequently, NH 3 -SCR technology coupled with CO oxidation reaction is a promising approach for simultaneous NO and CO removal. In this study, a series of bifunctional CuO x /MnO 2 catalysts were synthesized using a combine of hydrothermal and wet impregnation methods, and their catalytic performance for simultaneous removal of NO and CO was assessed. CuO x /α-MnO 2 catalyst displayed outstanding catalytic activity for both NO and CO, achieving over 80 % NO removal efficiency and 96 % CO conversion rate at 150 °C, while CuO x /β-MnO 2 catalyst exhibited poor catalytic activity in the entire temperature range. Moreover, the interplay between the NH 3 -SCR and CO catalytic oxidation reactions was also explored. XPS results revealed that the concentration of Mn4+ and Cu+ species significantly influenced the catalytic activity of the catalysts for the simultaneous removal of NO and CO. Particularly, the presence of Mn4+ species promoted "fast SCR" reaction, whereas Cu+ species demonstrated higher reactivity for both NO reduction and CO oxidation. In situ DRIFTS analysis of transient reactions revealed that the L-H mechanism was followed over CuO x /α-MnO 2 catalyst in the NH 3 -SCR reaction, while both the M-K and L-H mechanisms were observed in CO catalytic oxidation reaction. [ABSTRACT FROM AUTHOR]

In the selective catalytic reduction (SCR) of NO x with NH 3 , a catalyst usually exhibits a seesaw effect on de-NO x activity and N 2 selectivity at low temperatures. Herein, we designed metal-organic frameworks (MOFs) with dual-ligand coordination to regulate the electronic and morphological structure for a breakthrough of the seesaw effect. The developed catalyst attained a noteworthy NO x conversion exceeding 90% within 60–330 ℃ with increased N 2 selectivity. The dual-ligand coordination leads to more defects and a more uniform electron distribution for delocalization of electrons, thereby improving de-NO x activity. Furthermore, the dual-ligand coordination manifests a Si-O-Mn bond for amplifying both de-NO x activity and thermal stability. Additionally, the dual ligands and Mn produce a hollow sea-urchin-like morphology with more exposed active sites for concentrating reactants and intermediates to improve electron transfer efficiency in N 2 selectivity. This work clarifies the mechanism of dual-ligand regulation for electron-morphology to simultaneously enhance de-NO x activity and N 2 selectivity. [Display omitted] • TEOS&Mn-BTC with more defects and structure tunability is designed by dual-ligand coordination. • Si-O-Mn bond formed by dual ligands leads to electron-metal-carrier coordination structure. • Self-assembly of block copolymers with ligands and Mn forms hollow sea-urchin-like microsphere. • The electron-morphology regulation breaks the seesaw effect between activity and selectivity. [ABSTRACT FROM AUTHOR]

CuO@TiO2 core–shell nanostructure catalyst with CuO core and TiO2 shell was prepared by a two-step method and then used in NH3-SCR reaction. FE-SEM, TEM and element mapping were used to investigate the morphologies of the sample. Their results indicated CuO nanorods were coated with TiO2 and thus forming a core–shell nanostructure. According to the results of N2 adsorption–desorption, XRD, Raman, XPS, NH3-TPD, H2-TPR and in situ DRIFTS, the core–shell nanostructure would benefit the formation of better redox ability, more oxygen vacancies, more acid sites and abundant adsorbed NOx species on the catalyst. Thus, the core–shell nanostructure catalyst presented significantly higher activity than pure CuO and TiO2. NH3-SCR reaction on CuO@TiO2 core–shell catalyst should follow both Eley–Rideal (E-R) mechanism and Langmuir-Hinshewood (L–H) mechanism. These findings may promote the development of the new effective non-vanadium-based SCR catalysts. [ABSTRACT FROM AUTHOR]

CuSO 4 /TiO 2 catalysts with high catalytic activity and excellent resistant to SO 2 and H 2 O, were thought to be promising catalysts used in Selective catalytic reduction of nitrogen oxides by NH 3. The performance of catalysts is largely affected by calcination temperature. Here, effects of calcination temperature on physicochemical property and catalytic activity of CuSO 4 /TiO 2 catalysts were investigated in depth. Catalyst samples calcined at different temperatures were prepared first and then physicochemical properties of the catalyst were characterized by N 2 adsorption-desorption, X-ray diffraction, thermogravimetric analysis, Raman spectra, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, temperature-programmed desorption of NH 3 , temperature-programmed reduction of H 2 and in situ diffuse reflectance infrared Fourier transform spectroscopy. Results revealed that high calcination temperature had three main effects on the catalyst. First, sintering and anatase transform into rutile with increase of calcination temperature, causing a decrement of specific surface area. Second, decomposition of CuSO 4 under higher calcination temperature, resulting in disappears of Brønsted acid sites (S–OH), which had an adverse effect on surface acidity. Third, CuO from the decomposition of CuSO 4 changed surface reducibility of the catalyst and favored the process of NH 3 oxidation to nitrogen oxides (NO x). Thus, catalytic activity of the catalyst calcined under high temperatures (≥600°C) decreased largely. Image 1 [ABSTRACT FROM AUTHOR]

• Dy was used as a dopant to modify MnFe mixed oxides for SCR catalyst for the first time. • The effects of Dy on the physical and chemical properties of MnFeO x were well disclosed. • MnFeDy-0.1 exhibited excellent low-temperature de-NO x performance and N 2 selectivity. • The reason dominated the NH 3 and NO adsorptions was revealed by DFT calculation. • The reaction mechanisms over the MnFeDy-0.1 were fully revealed by in-situ DRIFT. Recently, Mn-based catalysts doped/modified by rare earth elements for the selective catalytic reduction (SCR) of NO x with NH 3 are becoming a new research hotspot. In current work, Dy-doped MnFe oxides with the morphology of one-dimensional nanowire are successfully prepared by using electrospinning method for the first time, and the catalytic performances for the NH 3 -SCR of NO x are investigated in detail. It is found several positive factors are introduced due to the doping of Dy with an appropriate amount, such as the enhanced surface Mn4+ concentration and surface chemical adsorption of oxygen, the increased adsorption capacity for NH 3 and NO. Theoretical calculation reveals that the Dy-doping causes the larger depletion of electron density of mainly O atoms on the surface of MnFeDy than that of MnFe case, which energetically favors the adsorption of NH 3 and NO molecules. Our results fully confirm that Dy is an effective doped element of Mn-based catalysts for developing SCR catalysts with excellent low-temperature de-NO x performance. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Facet-dependent de-NO x based on α-Mn 2 O 3 was investigated for the first time. • The new active sites on (0 0 1) facets induced by charge redistribution are revealed first. • The experimental results and DFT calculated results are well verified by each other. • New insights into the understanding of crystal-facet-dependent reactivity are provided. Abstract Crystal facets usually play an important role in the catalytic activity of inorganic single crystals. In this work, two α-Mn 2 O 3 single crystals with an octahedron (exposed with (1 1 1) facet) and a truncated octahedron (exposed with both (1 1 1) and (0 0 1) facets) were successfully prepared by a simple solvent-thermal reaction, and their catalytic activities were evaluated by the selective catalytic reduction (SCR) of NO x with NH 3. The results show that the catalytic performance of the α-Mn 2 O 3 single crystal with a truncated octahedron was enhanced in comparison with the α-Mn 2 O 3 single crystal with an octahedron by the exposure of a small fraction of (0 0 1) facets. This can be attributed to the new active sites created by charge redistribution on the surface of the (0 0 1) facets, which provides more adsorption sites, facilitating the further adsorption and reaction of NH 3 and NO molecules, and thereby enhancing the catalytic performance. This work should provide new insight into the understanding of crystal-facet-dependent reactivity and important guides for the design and preparation of SCR catalysts with high activity. [ABSTRACT FROM AUTHOR]

A series of Ni y Co 1-y Mn 2 O x microspheres (MSs) (y = 0.1, 0.3, 0.5, 0.7, 0.9) were synthesized successfully by a hydrothermal method. Their physicochemical properties of the as-prepared Ni y Co 1-y Mn 2 O x MSs were explored by using a series of characterizations, and their catalytic performances were evaluated by the selective catalytic reduction (SCR) of NO x with NH 3 . It was found that there are the synergetic effects between Ni and Co, which have an important impact on the surface physicochemical properties of Ni y Co 1-y Mn 2 O x MSs, such as the roughness of the surface, the stacking molding, the crystal structure, the specific surface area, the concentrations of surface Mn 4+ , Co 3+ and Ni 2+ , the reducibility, and the proportion of weak acid and strong acid sites, etc, which further affect the reaction mechanism of de-NO x of Ni y Co 1-y Mn 2 O x MSs, and finally dominate their catalytic performances for the SCR of NO x with NH 3 . Among all Ni y Co 1-y Mn 2 O x MSs, Ni 0.7 Co 0.3 Mn 2 O x exhibits the optimal catalytic performance for the SCR of NO x , which is much better than CoMn 2 O x and NiMn 2 O x . This work may shed light on the deliberately designed Mn-based SCR catalysts with high activity by taking advantage of the synergetic effects between components. [ABSTRACT FROM AUTHOR]

Effects of propane/methane ratios on NO x reduction by mixtures of methane and propane over In/H-BEA catalyst were investigated at temperatures ranging from 250 to 550 °C. The higher catalytic activity of In/H-BEA was exhibited for CH 4 -SCR at high temperatures above 450 °C, while the higher NO x conversion was achieved in C 3 H 8 -SCR at below 425 °C. A broadened temperature window and enhanced CO 2 selectivity were achieved by combining of methane and propane as the co-reductant. The mixtures with propane/methane of 1/2 showed the most superior T 50 (325 °C) and T 90 (500 °C) temperatures for NO x reduction over In/H-BEA catalyst. For the promotion mechanism of propane on NO reduction by methane at low temperature, the formation of carbonaceous species (e.g. R-COOH) were enhanced by the activation of C 3 H 8 on Brønsted acid sites at low temperature, and further promoted the generation of NCO species, which was a crucial determining step for NO reduction. [ABSTRACT FROM AUTHOR]

A novel MnO x -CeO 2 catalyst with shell-in-shell microsphere structure was successfully prepared by a one-step hydrothermal method for the first time. The obtained catalyst was characterized by SEM, TEM, XRD, N 2 adsorption and desorption, XPS, H 2 -TPR and NH 3 -TPD in detail, and its catalytic activity was investigated by selective catalytic reduction of NO x with NH 3 . The results showed that the MnO x -CeO 2 microsphere catalyst presented high catalytic activity at low temperatures (lower than 210 °C), which was much superior to the counterpart MnO x -CeO 2 catalyst without shell-in-shell microsphere structure prepared by co-precipitation method. [ABSTRACT FROM AUTHOR]

The deposition of K can lead to deactivationof commercial V2O5–WO3/TiO2selectivecatalytic reduction (SCR) catalyst while the presence of SO2largely increases the activity of K-poisoned catalyst. For revealingthe mechanism of the SO2effect on the SCR reaction, theK-poisoned catalyst was prepared by impregnation of KNO3solution and in situ diffuse reflectance infrared Fourier transformspectroscopy (DRIFTS) was carried out on the fresh and K-poisonedcatalyst. The results showed that the adsorption of SO2in the presence of O2was different between fresh andK-poisoned catalyst. The tridentate sulfate was formed with titaniumin the fresh catalyst. While on the K-poisoned catalyst, the bidentatesulfate was likely formed with vanadium, which increased the numberof Brønsted acid sites and the activity of the catalyst significantly. [ABSTRACT FROM AUTHOR]

A new thulium (Tm) modified Mn/TiO 2 catalyst is firstly prepared to remove NO at low temperature, where the TiO 2 with relatively high specific surface area (184.3 m2/g) is used as carrier to support the active component MnO x , and Tm is utilized as promoter to modify the MnO x. The developed Tm–Mn/TiO 2 catalyst presents significantly improved selective catalytic reduction (SCR) de-NO x performance at low temperature with NH 3 as reducing agent. It is found that after an appropriate content of Tm is introduced, the surface concentration of Mn4+, the chemical adsorbed oxygen, the chemisorption of NH 3 and NO, and the reducibility of the Tm–Mn/TiO 2 catalyst are improved, which are helpful to the enhancement of NH 3 -SCR de-NO x performance. Moreover, it is discovered that, over Tm–Mn/TiO 2 catalyst, an Eley-Rideal (E-R) mechanism occurs in the reaction between adsorbed NH 3 species connected by Lewis acid sites and gaseous NO, meanwhile, a Langmuir-Hinshelwood (L-H) mechanism occurs between adsorbed NH 3 species and adsorbed NO species, where the E-R mechanism dominates the NH 3 -SCR de-NO x process. Image 1 • Tm was used as a dopant to modify Mn/TiO 2 catalyst for the SCR de-NO x for the first time. • The effects of Tm on the physical and chemical properties of Mn/TiO 2 were well disclosed. • Tm 0.1 Mn/TiO 2 exhibited excellent low-temperature de-NO x performance and N 2 selectivity. • The reaction mechanisms over the Tm 0.1 Mn/TiO 2 were fully revealed by in-situ DRIFTS. [ABSTRACT FROM AUTHOR]

The Al 2 O 3 additive can be beneficial to boost the decomposition of NH 4 HSO 4 and inhibit the reaction between MnO x and SO 2. • Based on the deactivation mechanism of MnO x , the optimal additive was screened out. • Al 2 O 3 was first used as an additive to enhance the SO 2 tolerance of MnO x. • The MnAl oxide showed enhanced low-temperature de-NO x activity and SO 2 tolerance. • The introduction of Al 2 O 3 into MnO x can facilitate the decomposition of NH 4 HSO 4. This research aims to enhance the SO 2 tolerance of manganese oxide (MnO x) catalysts for low-temperature selective catalytic reduction (SCR) de-NO x. Based on the deactivation mechanism of MnO x , we target at the promotion of the byproduct (NH 4 HSO 4) decomposition and the inhibition of the byproduct (MnSO 4) formation. To achieve this target, thermogravimetric (TG) and temperature programmed desorption of SO 2 (SO 2 -TPD) are performed upon as many as 21 kinds of single metal oxides to explore the potentially effective chemical composition as the additive of MnO x catalysts. The TG result indicates that Al 2 O 3 can remarkably decrease the thermal stability of NH 4 HSO 4. In addition, the SO 2 -TPD analysis reveals that the formed species after SO 2 adsorption are weakly adsorbed on Al 2 O 3. Thus, Al 2 O 3 is selected to mix with MnO x to optimize its SO 2 tolerance. Further experimental results demonstrate that the proper introduction of Al 2 O 3 can effectively enhance the low-temperature SCR de-NO x activity and the SO 2 tolerance of MnO x. It is revealed that the introduction of Al 2 O 3 into MnO x can not only facilitate the decomposition of NH 4 HSO 4 but also lead to reduced thermal stability of the adsorbed SO 2 species to some extent. As compared to the pristine MnO x , the slight introduction of Al 2 O 3 as the additive is beneficial to the low-temperature SCR de-NO x activity and SO 2 tolerance of MnO x. [ABSTRACT FROM AUTHOR]