Catalysts For Low-temperature NH3-SCR Research Articles

Revealing the promotional effect of Ce doping on the low-temperature activity and SO2 tolerance of Ce/FeVO4 catalysts in NH3-SCR

Elimination of NOx from the non-electric industrial boilers has become priority under the effective implementation of ultra-low emissions. A series of Ce-promoted FeVO4 catalysts with improved acidity and reducibility have been synthesized in this work. Thereinto, 10Ce/FeVO4 exhibited an optimum low-temperature performance with 90% of NOx conversion and 95% of N2 selectivity at 200–300 °C which was kept nearly unchanged with different concentrations of SO2 ranging from 50 ppm to 200 ppm, showing a superior sulfur tolerance. An array of well-designed experiments has demonstrated that Ce mainly existed as CeVO4 under a low doping content (1 wt%) on FeVO4, which could efficiently increase the amount of acid sites. With more cerium (5–12 wt%) loading on FeVO4, the appearance of CeO2 further resulted in a strong interaction between cerium species and ion species, thus significantly improving the low-temperature catalytic activity. Therefore, the optimum coexistence of CeVO4 and CeO2 over 10Ce/FeVO4 modulated its Brønsted acid and enhanced its redox circulation of Fe3+ species. Moreover, the NH3-SCR reaction pathways of 10Ce/FeVO4 were broadened from only Eley-Rideal to both Eley-Rideal and Langmiur-Hinshelwood mechanisms after Ce loading on FeVO4 catalyst. With the presence of SO2, the SO/S-O deriving from the generated Ce2(SO4)3 and NH4HSO4 increased the Brønsted acid sites, inducing a satisfying SO2 tolerance of 10Ce/FeVO4 catalyst, although the Langmiur-Hinshelwood pathway of 10Ce/FeVO4 was immediately cut off due to the competitive adsorption of gaseous SO2 and NOx. This work exemplifies a promising strategy for developing an ideal low-temperature NH3-SCR catalyst with good SO2 resistance.

MnOx-pillared rectorite prepared by in situ deposition as efficient catalysts for low-temperature NH3-SCR: The influences of manganese (II) precursors

MnO x pillared rectorite (REC) catalysts (10 wt% based upon Mn element and the mass of clay) were prepared by in situ deposition using different manganese (II) precursors, e.g., Mn(NO 3 ) 2 , Mn(Ac) 2 , MnSO 4 and MnCl 2 to react with KMnO 4 , respectively. Unsupported MnO x was also prepared through reaction between Mn(Ac) 2 and KMnO 4 solution. The samples were characterized by XRD, SEM, low-temperature N 2 adsorption, HRTEM, H 2 -TPR, NH 3 -TPD, TPSR and XPS. And the deNO x performances for low-temperature NH 3 -SCR were evaluated. The results showed that the unsupported amorphous MnO x had much higher deNO x performance than different MnO 2 phases. For the MnO x pillared REC catalysts, deNO x performances decreased in the order of Mn10/REC-Ac - > Mn10/REC-Cl - > Mn10/REC-SO 4 2- > Mn10/REC-NO 3 - . The Mn10/REC-AC - MnO x -Ac - /REC showed the best redox properties, richest weak acid sites and best dispersion of MnO x and content of Mn 4+ , which contributed to its high activity. Moreover, even under working conditions with GHSV up to 105,000 h −1 , high deNO x performance and good stability was also observed for Mn10/REC-Ac - catalyst. • Simple way to prepare pillared layered clays (PILCs) for NH3-SCR was developed through in situ deposition. • manganese (II) precursors influenced ion exchange, catalyst prepared using Mn(Ac) 2 showed the best deNO x performance. • High content and good dispersion of MnO x, rich weak acid sites, good redox property all contribute to high deNO x performance.

Facile control of surface properties in CeO2-promoted Mn/TiO2 catalyst for low-temperature selective catalytic reduction of NO by NH3

Although the metal loading sequence can highly influence the bimetallic catalyst performance, they are generally applied to the reaction experiments without investigating the metal impregnation sequence. In this study, therefore, we investigated the surface properties of CeO2-promoted Mn/TiO2 catalysts with different impregnation sequences of Mn and Ce in the low-temperature selective catalytic reduction (SCR) of NO by NH3. We observed that the catalyst performance depended on simply changing the impregnation method of Mn and Ce in the catalyst activity test for the low-temperature SCR reaction. The co-impregnated catalyst, Mn-Ce/TiO2, achieved much higher NO conversion than other catalysts. Additionally, X-ray diffraction, transmission electron microscopy, N2 adsorption/desorption experiments, H2 temperature-programmed reduction (H2-TPR), NO/NH3 temperature-programmed desorption (NO/NH3-TPD), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FTIR) were performed to identify the influence of this simple change on the catalyst. These characterization results indicated that metal dispersion improved in the co-impregnated catalyst compared to the sequentially impregnated catalysts, and these well-distributed metal particles (Mn-Ce/TiO2 catalyst) could produce defect formation on the catalyst, thereby serving more NOx/NH3 adsorption sites. Moreover, it was found that catalyst acidity could be simply controlled by changing synthesis method although it contained same metal composition. This knowledge will be useful for the design of catalyst for low temperature NH3-SCR of NO.

Structural control for inhibiting SO2 adsorption in porous MnCe nanowire aerogel catalysts for low-temperature NH3-SCR

• Hierarchical porous nanowire aerogel catalysts with excellent NH 3 -SCR performance. • SO 2 promotes the adsorption activation of NH 3 on the MnCe-N catalyst. • The nanowire structure increases the specific surface area and the surface acidity. • Nanowire structure effectively inhibits SO 2 adsorption and sulfate generation. The presence of SO 2 in industrial flue gases will cause permanent deactivation of the catalyst active centre. Therefore, an effective method to improve the SO 2 resistance of manganese-based catalysts at low temperatures is urgently needed. In this work, a hierarchical porous nanowire structure catalyst was designed by the in situ self-assembly method to inhibit SO 2 adsorption. This hierarchical porous nanowire aerogel catalyst with great BET surface area and surface acidity exhibited NOx conversion above 90% at 100–400 °C. Notably, the NOx conversion of the MnCe-N catalyst was almost not inhibited by SO 2 (250 ppm) compared to the 33% decrease of the MnCe-P catalyst. On the MnCe-P catalyst, SO 2 has strong competitive adsorption with NH 3 and NO, and the stronger adsorption capacity of SO 2 inhibits the adsorption activation of the reaction gas and hinders the reaction proceeding through the L-H mechanism. Meanwhile, a large quantity of sulfate is formed on the catalyst surface, which prevents the active centre to participate in the redox reaction. The structure of nanowires enhances the number of acid sites, facilitates the adsorption and activation of NH 3 , and effectively inhibits the adsorption of SO 2 on the MnCe-N catalyst. Fewer sulfate species are generated and difficult to deposit and aggregate on the catalyst surface, as a result, the active centre is less affected by sulfate species. The stable adsorption of NH 3 -related species ensures reliable reaction on MnCe-N through the E-R mechanism. This work emphasizes the importance of hierarchically porous structures in improving the NH 3 -SCR performance and SO 2 resistance of monolithic catalysts, and provides new insights into the design of highly efficient and stable catalytic materials.

Promotion of Ilmenite Blending on Anti-Sulfur Performance of Mnfe/Z Catalyst for Low-Temperature Nh3-Scr

Promotion of Ilmenite Blending on Anti-Sulfur Performance of Mnfe/Z Catalyst for Low-Temperature Nh3-Scr

Reuse of Spent Fcc Catalyst as Support to Prepare Efficient Manganese-Based Low-Temperature Nh3-Scr Catalysts

Reuse of Spent Fcc Catalyst as Support to Prepare Efficient Manganese-Based Low-Temperature Nh3-Scr Catalysts

Significantly enhanced activity and SO2 resistance of Zr-modified CeTiOx catalyst for low-temperature NH3-SCR by H2 reduction treatment

• The Zr-modified CeTiO x mixed oxide catalyst was reduced by H 2 for NH 3 -SCR. • R-CZT-20/1 catalyst exhibited outstanding low-temperature activity and excellent SO 2 resistance. • The R-CZT-20/1 sample enriched Ce 3+ , oxygen vacancies, strong synergistic effect between Ce-Zr-Ti. • The reduced R-CZT-20/1 obeyed the L-H mechanism. The Zr-modified CeTiO x mixed oxide catalyst with good NH 3 -SCR activity and SO 2 resistance was synthesized and reduced by H 2 . Performance test revealed that the obtained R-CZT-20/1 (Ce: Zr: Ti = 20: 1: 100) catalyst exhibited outstanding low-temperature activity after H 2 reduction treatment, which achieved upon 98% NO conversion at 200–350 °C. Remarkably, it possessed excellent SO 2 resistance as well as good reversibility, with the activity decreased from 100% to 96%. Meanwhile, R-CZT-20/1 possessed more surface acid sites and oxygen defects, which promoted the chemical adsorption and activation of NO and NH 3 on the catalyst surface. XPS results confirmed that R-CZT-20/1 enriched Ce 3+ , accelerated the electron transfer between Ce 3+ + Ti 4+ → Ce 4+ + Ti 3+ , and generated a large number of oxygen vacancies. Moreover, there is strong synergistic effect between Ce-Zr-Ti, which might be the reason for the excellent SO 2 resistance. Among them, the presence of Zr facilitated the favorable process. In situ DRIFTS experiments indicated that the unreduced catalysts followed E-R and L-H mechanism at low and high temperatures, respectively, while R-CZT-20/1 obeyed only the L-H mechanism.

Excellent low-temperature NH3-SCR of NO activity and resistance to H2O and SO2 over WaCeOx (a = 0.06, 0.12, 0.18, 0.24) catalysts: Key role of acidity derived from tungsten addition

Bimetallic W a CeO x (a = 0.06, 0.12, 0.18, 0.24) catalysts were synthesized for selective catalytic reduction of NO x with NH 3 (NH 3 -SCR). The influences of W on structure, activity and surface properties were investigated by XRF, XRD, Raman, TEM, N 2 adsorption-desorption, H 2 -TPR, O 2 /NH 3 /SO 2 -TPD, XPS, and in-situ DRIFTS. The characterization results show that the W/Ce ratio has a great effect on the NH 3 -SCR activity. The different catalytic activities of W a CeO x are mainly attributed to the acidity change, especially the increase of B-acid content plays a major role in enhancing low temperature activity. W 0.18 CeO x exhibits excellent low-temperature NH 3 -SCR activity, SO 2 /H 2 O resistance and N 2 selectivity with a broad activity window (190–490 °C) with 5%H 2 O. Moreover, good activity window (235–460 °C) can be maintained even the catalyst treated with 5% H 2 O at 800 °C for 12 h, showing especial hydrothermal stability. Thus, it can be summarized that W 0.18 CeO x is regarded as outstanding catalyst for low-temperature NH 3 -SCR of NO. • An excellent low temperature NH 3 -SCR catalyst, W 0.18 CeO x bimetallic oxide. • Increased content of B acid site due to the introduction of a small amount of W. • More B acid sites contribute to good activity and wide activity temperature window. • Good resistance to H 2 O/SO 2 over W 0.18 CeO x bimetallic oxide.

TiO2-carbon nanotubes composite supported MnOx-CuO catalyst for low-temperature NH3-SCR of NO: Investigation of SO2 and H2O tolerance

• Mn-based SCR catalysts with different CuO content were analyzed and tested over TiO 2 /CNTs composite support for NO conversion. • Effect of CuO and CNTs addition to Mn/Ti catalyst on H 2 O/SO 2 resistance was investigated. • Test results depicted that addition of 5 wt% CuO was sufficient to achieve better NO conversion in the temperature regime of 150–350 °C. • Remarkable low temperature SCR activity was achieved with the addition of CuO to Mn/Ti-C catalyst. A series of titania-carbon nanotubes (TiO 2 -CNTs) supported MnOx-CuO catalysts were prepared and investigated for NH 3 -SCR of NO at low temperature. It was observed that the addition of Cu and/or CNTs to Mn/TiO 2 has a beneficial effect in improving the activity of the catalyst. In addition, the effect of Cu loading was also studied and found that the catalyst with 5 wt% Cu (Mn-Cu 5 /Ti-CNTs) exhibited the best NH 3 -SCR performance. Remarkably, the Mn-Cu 5 /Ti-CNTs showed excellent resistance to SO 2 /H 2 O in comparison to the Mn/TiO 2 catalyst. The addition of CNTs has increased the specific surface area, total pore volume, and reduced the average pore size of the catalyst. Meanwhile, the Cu loading has enhanced the Mn 4+ species and chemisorbed oxygen species on the surface of the catalyst. Besides, the incorporation of both Cu and CNTs have decreased the catalyst reduction temperature and increased the amount and strength of acidic sites on the catalyst. All these factors contributed to the superior NH 3 -SCR activity and SO 2 /H 2 O resistance of the catalyst.

Comparative study on the physicochemical properties and de-NOx performance of waste bamboo-derived low-temperature NH3-SCR catalysts

Comparative study on the physicochemical properties and de-NOx performance of waste bamboo-derived low-temperature NH3-SCR catalysts

Effects of Sm modification on biochar supported Mn oxide catalysts for low-temperature NH3-SCR of NO

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 NH3 (LT NH3-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 NH3-SCR activity with the NO conversion of 85% at 200 °C and best N2 selectivity in a broad temperature range of 75–250 °C. Doping with Sm species, Mn4+ + Mn3+/Mnn+ and Oα/Oβ 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 N2 selectivity. In addition, weak and medium acid increased markedly after the Sm species added on catalysts, causing more active sites for SCR reaction. The NH3-SCR reaction of Sm(0.2)-Mn/BC catalyst followed the L-H mechanism, and the generation of intermediate –NH2, NH4+ species and the NxOy species were observed which played vital part in the LT NH3-SCR reaction.

Single-atom iron as a promising low-temperature catalyst for selective catalytic reduction of NOx with NH3: A theoretical prediction

• A novel single atom iron catalyst for NH 3 -SCR. • Environmentally friendly Fe 1 -N 4 with high low-temperature efficiency. • Reaction mechanism in atomic level and microkinetic modeling. Selective catalytic reduction of NO x with NH 3 (NH 3 -SCR) is a dominant technology to reduce NO x (deNO x ). However, there are two shortcomings for commercial deNO x catalysts (vanadium-titanium-based metal oxides), such as poor low-temperature efficiency and toxicity. Thus, it is urgent to develop environmentally friendly low-temperature catalysts with high deNO x efficiency. Therefore, we firstly proposed a single-atom iron coordinated with four N atoms (Fe 1 -N 4 ) as a novel low-temperature NH 3 -SCR catalyst, due to its high coordination unsaturation and safety. The detailed reaction mechanisms are revealed via density functional theory calculations and microkinetic modeling. Seven possible reaction pathways were found in the NH 3 -SCR reaction. Different from metal oxides, special intermediates such as N 2 H and NHNO are found in the reaction pathway. The dominant pathway of the NH 3 -SCR reaction over the Fe 1 -N 4 catalyst is a three-step process including NO oxidation, NO 2 reduction, and NHNO decomposition. The suitable temperature window of the Fe 1 -N 4 catalyst is <430 K due to its relatively low energy barrier of 0.99 eV. Different from other metal oxide catalysts, the fast oxidation of NO on Fe 1 -N 4 catalyst significantly promotes the reaction rate of NH 3 -SCR on Fe 1 -N 4 catalyst. Based on its outstanding performance, we believe that single Fe atom catalyst can provide new insights to design novel catalysts for NH 3 -SCR.

Activating low-temperature NH3-SCR catalyst by breaking the strong interface between acid and redox sites: A case of model Ce2(SO4)3-CeO2 study

• Novel effect of strong acid-redox interface hinders NH 3 -SCR activity is reported. • Three Ce 2 (SO 4 ) 3 -CeO 2 catalysts with distinct interfaces are constructed. • NO adsorption and oxygen vacancy formation are limited after Ce 2 (SO 4 ) 3 addition. • Weak interface promotes NO activation and the formation of active nitrites. The occurrence of NH 3 -SCR (selective catalytic reduction of NO with NH 3 ) reaction on catalyst surface typically requires acid and redox sites. However, the role of acid-redox interaction on NH 3 -SCR performance is still obscure due to complex acidities and entangled acid-redox sites. Herein, three types of model Ce 2 (SO 4 ) 3 -CeO 2 catalysts with distinct interfaces are constructed to reveal the effect of acid-redox interaction on NH 3 -SCR performance. That is, SO 4 2- /CeO 2 -VS (vapor sulfation of ceria) with strong acid-redox interfacial contact, SO 4 2- /CeO 2 -WI (wet impregnation), and SO 4 2- /CeO 2 -SG (solid grinding) with limited interfaces. It is found the redox property is significantly disturbed as a result of the electron-withdrawing effect from the sulfate. Theoretical result unravels that the introduction of Ce 2 (SO 4 ) 3 retards the oxygen vacancy formation over CeO 2 . Due to restricted interfaces in SO 4 2- /CeO 2 -SG, the negative influence from acid sites is greatly alleviated. Further mechanism study discloses the weakened acid-redox interaction actually changes the nature of surface NO x species, resulting in the generation of reactive species (*O-N-O* and cis -N 2 O 2 2- ) and the promotion of surface reaction via Langmuir-Hinshelwood (L-H) mechanism.

Application of manganese-containing soil as novel catalyst for low-temperature NH3-SCR of NO

Manganese-containing soil (M-S) is a solid waste generated from the mining and extraction of manganese ore. In this study, the low-temperature denitration performance of Mn-S was investigated via XRF, XRD, XPS, H 2 -TPR, NH 3 -TPD and DRIFTS, aiming at exploring its utilization approach as low-temperature NH 3 -SCR catalyst. The results showed that Mn-S exhibited a relatively high catalytic activity reaching over 75% NO conversion from 150 °C to 200 °C. The physical and chemical properties of Mn-S were studied, indicating that the manganese content of Mn-S reached 8.2% with mainly surface Mn atomic valence state of Mn 3+ . In situ DRIFTS results revealed the SCR reaction mechanism of Mn-S, suggesting that Mn-S obeyed the E-R reaction mechanism. The Ce/Mn-S catalyst was synthesized by impregnation method. The denitration activity improved and reached 92.4% at 200 °C. A series of characterizations were studied to investigate the strengthening mechanism after doping Ce. It’s found that introducing of Ce could increase the content of Mn 4+ and chemisorbed oxygen, NH 3 adsorption capacity and reducibility. It was found from in situ DRIFTS experiments that doping of Ce changed the reaction mechanism due to the conversion of inactive substance, which was mainly affected by E-R and L-H. • The excellent low-temperature denitration performance of Mn-S was investigated. • Ce-dropped Ce/Mn-S catalyst exhibited high denitration performance and improved N 2 selectivity. • Doping Ce enhanced the content of Mn 4+ and chemisorbed oxygen. • Supporting Ce changed the SCR reaction mechanism due to the conversion of inactive substance.

Spherical Al-MCM-41 Doped with Copper by Modified TIE Method as Effective Catalyst for Low-Temperature NH3-SCR.

Aluminum containing silica spherical MCM-41 was synthesized and modified with copper by the template ion-exchange method (TIE) and its modified version, including treatment of the samples with ammonia solution directly after template ion-exchange (TIE-NH3). The obtained samples were characterized with respect to their chemical composition (ICP-OES), structure (XRD), texture (low temperature N2 sorption), morphology (SEM-EDS), form and aggregation of deposited copper species (UV-vis DRS), reducibility of copper species (H2-TPR), and surface acidity (NH3-TPD). The deposition of copper by the TIE-NH3 method resulted in much better dispersion of this metal on the MCM-41 surface comparing to copper introduced by TIE method. It was shown that such highly dispersed copper species, mainly monomeric Cu2+ cations, deposited on aluminum containing silica spheres of MCM-41, are significantly more catalytically effective in the NH3-SCR process than analogous catalysts containing aggregated copper oxide species. The catalysts obtained by the TIE-NH3 method effectively operated in much broader temperature and were less active in the side process of direct ammonia oxidation by oxygen.

Improving the Performance of Gd Addition on Catalytic Activity and SO2 Resistance over MnOx/ZSM-5 Catalysts for Low-Temperature NH3-SCR

SO2 poisoning is a great challenge for the practical application of Mn-based catalysts in low-temperature selective catalytic reduction (SCR) reactions of NOx with NH3. A series of Gadolinium (Gd)-modified MnOx/ZSM-5 catalysts were synthesized via a citric acid–ethanol dispersion method and evaluated by low-temperature NH3-SCR. Among them, the GdMn/Z-0.3 catalyst with the molar ratio of Gd/Mn of 0.3 presented the highest catalytic activity, in which a 100% NO conversion could be obtained in the temperature range of 120–240 °C. Furthermore, GdMn/Z-0.3 exhibited good SO2 resistance compared with Mn/Z in the presence of 100 ppm SO2. The results of Brunauer–Emmett–Teller (BET), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction of H2 (H2-TPR) and temperature-programmed desorption of NH3 (NH3-TPD) illustrated that such catalytic performance was mainly caused by large surface area, abundant Mn4+ and surface chemisorbed oxygen species, strong reducibility and the suitable acidity of the catalyst. The in situ diffuse reflectance infrared Fourier transform spectra (DRIFTS) results revealed that the addition of Gd greatly inhibited the reaction between the SO2 and MnOx active sites to form bulk manganese sulfate, thus contributing to high SO2 resistance. Moreover, in situ DRIFTS experiments also shed light on the mechanism of low-temperature SCR reactions over Mn/Z and GdMn/Z-0.3, which both followed the Langmuir–Hinshelwood (L–H) and Eley–Rideal (E–R) mechanism.

Precursor Effect on Mn-Fe-Ce/TiO2 Catalysts for Selective Catalytic Reduction of NO with NH3 at Low Temperatures

Preparation of Mn/TiO2, Mn-Fe/TiO2, and Mn-Fe-Ce/TiO2 by the deposition-precipitation (DP) method can afford very active catalysts for low-temperature NH3-SCR (selective catalytic reduction of NO with NH3). The effect of precursor choice (nitrate vs. acetate) of Mn, Fe, and Ce on the physiochemical properties including thermal stability and the resulting SCR activity were investigated. The resulting materials were characterized by N2-Physisorption, XRD (Powder X-ray diffraction), XPS (X-ray photoelectron spectroscopy), H2-TPR (temperature-programmed reduction with hydrogen), and the oxidation of NO to NO2 measured at 300 °C. Among all the prepared catalysts 5MnAce/Ti, 25Mn0.75AceFe0.25Nit/Ti, and 25Mn0.75AceFe0.20NitCe0.05Ace/Ti showed superior SCR activity at low temperature. The superior activity of the latter two materials is likely attributable to the presence of amorphous active metal oxide phases (manganese-, iron- and cerium-oxide) and the ease of the reduction of metal oxides on TiO2. Enhanced ability to convert NO to NO2, which can promote fast-SCR like pathways, could be another reason. Cerium was found to stabilize amorphous manganese oxide phases when exposed to high temperatures.

Morphology control of metal-organic frameworks by Co-competitive coordination strategy for low-temperature selective catalytic reduction of NO with NH3

Morphology control of metal-organic frameworks (MOFs) has a great potential to achieve a superior performance for low-temperature selective catalytic reduction of NO with NH 3 (NH 3 -SCR). In this work, we reported a co-competitive coordination strategy to control the morphology of HKUST-1 with high pore accessibility and stability in an acid environment. Our results show that varying the dose of inorganic and organic modulators can facilitate the transformation of morphology of HKUST-1 between octahedron, cube, and tetrakaidekahedron. The HKUST-1 in tetrakaidekahedron is enriched with weak Lewis acid sites that lead to an enhancement of the NH 3 -SCR catalytic efficiency by 93% at low temperatures between 200 and 240 ​°C. The catalytic kinetic study further reveals that the activation energy of modified HKUST-1 is the lowest among reported materials. This work could provide a promising alternative strategy to advance the low-temperature NH 3 -SCR catalysts via precise morphology control. A co-competitive coordination strategy is developed to control the morphology of HKUST-1. The Lewis acidity varies with the morphology transformation. Taking the advantage of large amount of low-strength Lewis acid sites, the HKSUT-1-T exhibits an excellent NH 3 -SCR performance at 220 ​°C. • The morphology of HKUST-1 is controlled by a co-competitive coordination strategy. • Lewis acidity of HKSUT-1 is manipulated after morphology transfermation. • The modified HKUST-1 shows excellent catalytic activity at low-temperature NH 3 -SCR. • The activation energy of HKUST-1-T is the lowest among the reported materials.

NiMn2O4 sphere catalyst for the selective catalytic reduction of NO by NH3: Insight into the enhanced activity via solvothermal method

Herein, NiMn2O4 sphere (NiMn2O4-S) and NiMn2O4 particle (NiMn2O4-P) were fabricated via solvothermal method and ammonia precipitation method followed by calcination, then the two samples were evaluated as potential candidate catalysts for low temperature NH3-SCR. Meanwhile, systematical characterizations were employed to establish the relationship between denitrification performance and physiochemical properties. Besides, in-situ DRIFTs and kinetics calculation were performed to reveal the reaction mechanism and the intrinsic catalytic activity. The results verified the preferable catalytic performance of NiMn2O4-S with higher than 90% NO conversion at the range of 85–285 °C, and nearly 100% N2 selectivity at 120 °C. The fine catalytic activity might be related to the larger specific surface area, which could contribute to higher Mn4+/Mnn+ ratio, ampler Oα, more suitable acid amounts and redox capacity. In-situ DRIFTs revealed that the NH3-SCR over NiMn2O4-S and NiMn2O4-P catalysts mainly preceded via Eley–Rideal (E–R) mechanism at 90 °C. The higher TOF values and lower Ea value for NiMn2O4-S catalyst further confirmed its excellent de-NOx performance. As compared to NiMn2O4-P catalysts, the hierarchical spherical morphology of NiMn2O4-S catalyst could generate even more abundant NH3/NOx adsorption sites, higher reactivity of NH4+ bounded to Brønsted acid sites (NH4+-BASs) and NH2 species which were conducive to the enhancement of low temperature activity.

The influence of CNTs addition on Mn-Ce/TiO2 catalyst for low-temperature NH3-SCR of NO

Mn-Ce/TiO2 and Mn-Ce/TiO2-CNTs were tested for the low-temperature selective catalytic reduction of NO with NH3. The CNTs were in intimate contact with the catalyst surface, and the catalyst crystallinity, BET surface area, and porosity barely changed after CNTs addition. Compared to Mn-Ce/TiO2, Mn-Ce/TiO2-CNTs exhibited superior catalytic activity and N2 selectivity at 140–240 °C. High Mn4+ concentration and abundant chemisorbed oxygen species were found on the Mn-Ce/TiO2-CNTs. Monodentate nitrate species were mainly formed on Mn-Ce/TiO2-CNTs, which reacted with NH3, leading to a more reactive intermediate (Mn(n-1)+–O–NO2[NH3]2). Therefore, CNTs addition provided an enhanced favorable NOx adsorption sites resulting in high catalytic efficiency.