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Modulating the physicochemical properties of catalysts through the construction of special crystal structures or microscopic morphology provides new insights for developing high-performance low-temperature denitrification catalysts. This paper explores the effect of morphology structure on catalyst performance and identifies the dominant driving factors. The catalyst activity sequence was found to be MnO x spiny nanospheres (Mn-SNS) > MnO x nanowires (Mn-N) > MnO x nanospheres (Mn-NS) > MnO x nanoparticles (Mn-P). Among these, the Mn-SNS catalyst prepared by the hydrothermal method exhibited the best catalytic activity and the good resistance to water and sulfur. It achieved over 70% NO x conversion at 150 °C, and maintained 100% at 200–350 °C. In the presence of SO 2 and H 2 O, the NO x conversion was maintained at 87%. The spherical structure consisting of nanospikes provides the Mn-SNS catalysts with a large specific surface area, more (Mn4++Mn3+), abundant acid sites, and stronger reducibility, thus exhibiting excellent performance through the "fast-SCR" pathway. It also inhibits oxide crystallization and provides more sites for the adsorption activation of NO x and NH 3. The nanowire structures can provide a large specific surface area and a high concentration of Mn3+ and Mn4+ for MnO x catalyst. Characterization analyses revealed that the specific surface area, the ratio of (Mn4++Mn3+)/Mn, and the number of Lewis acid sites (L-NH 3) are the most important factors affecting the catalytic activity. This present empirical analysis provides new ideas for designing high-performance catalysts with a large specific surface area. [Display omitted] [ABSTRACT FROM AUTHOR]

BACKGROUND: In this paper, Mn–Co binary oxides prepared by an (NH4)2CO3‐assisted co‐precipitation method were used for the catalytic oxidation of NO at low temperatures. RESULTS: Experimental results showed that the Mn–Co binary catalysts prepared with manganese acetate and cobalt nitrate exhibited the highest oxidation activity, obtaining a NO conversion of 76% at 200 °C and 80% at 250 °C. The passivation effect of SO2 was found to be irreversible in the examination of the resistance to SO2 or/and H2O(g). Furthermore, characterization by X‐ray Photoelectron Spectroscopy (XPS), Fourier Transform infrared spectroscopy (FTIR), and in situ Diffuse Reflectance Infrared Fourier Transform spectroscopy (DRIFTs) revealed that the passivation effect was due to the bidentate and surface or bulk‐like sulfates generated on the surface of the catalyst. CONCLUSION: The analysis of intermediate species during the in situ DRIFTs characterization revealed that these sulfate species competed with nitrate/nitrite species for adsorption and affected the activity. Moreover, the poisoned catalysts could be regenerated to remove the majority of the bidentate and surface or bulk‐like sulfates from the surface and maintain the excellent NO catalytic oxidation activity. © 2021 Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

A series of MnCoOx flower-like hollow microspheres with various molecular proportions of reactant were prepared through simple solvothermal method for the ammonia selective catalytic reduction (SCR) at low temperatures. The as-prepared samples have been applied by various characterization techniques to explore the formation process of the morphology and physicochemical properties. The Mn(1)Co(1)Ox presented the optimal intrinsic catalytic performance (95% NOx conversion at 75 °C), favorable thermal stability, and strong SO2 resistance. The excellent properties mainly related to its higher specific surface area and abundant active sites originated from hollow microsphere special structure consists of abundant nanosheets, robust redox properties beneficial for the strong interaction between the manganese and cobalt, larger number of acidic sites and stronger acid strength, etc., which collaboratively dominate its catalytic properties of NH3-SCR at low temperatures. [ABSTRACT FROM AUTHOR]

[Display omitted] • 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. [ABSTRACT FROM AUTHOR]

MnCeOx/NF, Co/MnCeOx/NF and HMoP/Co/MnCeOx/NF catalysts were optimized step by step and used for the selective catalytic reduction (SCR) of NOx with NH 3. The catalytic performance, water/sulfur resistances and N 2 selectivity of the overall catalyst were significantly improved and maintained during above continuous optimization processes. Firstly, MnCeOx loaded 3D monolithic Ni-foam (MnCeOx/NF) catalysts were investigated using response surface methodology (RSM) method with central composite design (CCD). Regression equations and 3D response surface graphs showed that the model-predicted value was highly in line with experiment-actual result for the catalytic performances synchronously corresponding to load and calcination temperature, calcination and reaction temperature, which obtained 95.7% NOx conversion with 76.7% N 2 -selectivity at 179.5 °C over the optimal 16.5%MnCeOx/NF catalyst calcinated at 432 °C. Calcination temperature has a great influence on SCR activity that a suitable one increased the surface Mn4+, Ce3+ and chemical adsorption oxygen, while a high one visibly decreased NOx conversion due to the rapid weakened oxygen absorption and lattice oxygen content. The coexistence of typical Eley–Rideal and Fast -SCR reaction mechanisms were found over MnCeOx/NF, while the reaction rate of intermediates changed significantly but also reduced N 2 -selectivity due to the increased rate of side reactions as reaction temperature increasing. Secondly, among Co-, Ni- or Fe-modified catalysts, the optimized Co/MnCeOx/NF obtain an acceptable H 2 O and SO 2 resistance with stable NOx conversion above 72% within 10 h at 175 °C. Furthermore, phosphomolybdic acid modified Co/MnCeOx/NF catalyst maintained more than 80% N 2 -selectivity at 275 °C along with almost 100% NOx conversion within 175 °C–275 °C. These advantages synergistically accelerate the overall SCR performances of activity, selectivity and resistance of the optimized HMoP/Co/MnCeOx/NF catalyst. MnCeOx/NF (monolithic nickel foam) catalyst was optimized by response surface methodology (RSM) method using central composite design (CCD), and further improved the resistances to H 2 O and SO 2 by Co-doping and enhanced N 2 -selectivity by phosphomolybdic acid (HMoP) modification. [Display omitted] • Novel RSM method using CCD was adopted to analyse catalytic performances. • Model-predicted values was highly in line with the experiment-actual results. • Typical Eley–Rideal and Fast -SCR mechanisms coexisted on MnCeOx/NF surface. • HMoP greatly improved the capacities of medium-temperature redox and NH 3 adsorption. • Strong electron interaction with abundant adsorbed-oxygen resulted in good activity. [ABSTRACT FROM AUTHOR]

Simplified mechanism of SCR reactions on MnCo-CMS catalyst in different temperature ranges. • 3D MnCo-CMS flexible catalyst shows excellent NH3-SCR performance at low temperature. • Co doping into Mn-CMS increases reactive oxygen species and Lewis acid level, and reduce reaction energy barrier. • Co doping significantly increased the amount of surface active sites and thereby contributed to adsorption of reactant gas. • NH 3 -SCR reaction pathway depended on NH 3 or NO pre-adsorbed on the catalyst. In this article, a highly ordered MnCo nanoarray was grown in situ on a flexible nitrogen-doped carbon foam substrate (CMS) by a facile, stepwise ionic compound assisted hydrothermal route. The obtained metal oxides flexible catalyst has a unique three-dimensional structure, and MnCo nanoarray is uniformly grown on the CMS framework. Further, the low-temperature catalytic performance of selective catalytic reduction (SCR) of NOx with NH 3 was investigated. The results showed that the MnCo-CMS catalyst has excellent low-temperature activity and Co-doped can significantly enhance both H 2 O and SO 2 resistances. In addition, the relationship between the catalytic performance, redox performance and structure of metal oxides flexible catalysts was explored through SEM-EDS, XRD, BET, XPS and in-situ DRIFTS. All the analysis results indicated that doping Co in Mn-CMS catalyst could not only reduce the energy barrier of the reaction, but also increase active surface oxygen species and Lewis acid sites of the MnCo-CMS catalyst. The in-situ DRIFTS speculated that the reaction mechanism of NH 3 and NO on MnCo-CMS catalyst is temperature dependent. The low temperature range (<200 °C) conforms to the L-H mechanism, and the high temperature range (> 200 °C) may mainly follow the E-R mechanism. [ABSTRACT FROM AUTHOR]

• Ce-modified Mn-Fe catalysts showed higher SCR performance and SO 2 tolerance. • Good SCR activity might be attributed to more (Mn3++Mn4+) and Fe3+. • NO and NH 3 could be adsorbed on the catalyst surface in different forms. • The SCR reaction route mainly followed the Eley-Rideal mechanism. A series of metals doped Mn-Me-M x (Me = Fe, Cu, Ce; M x = Ce, Mg, Co, Ni, W) catalyst were synthesized by a co-precipitation method for low-temperature selective catalytic reduction of NO x with NH 3. The results showed that among the binary oxides catalysts, the Mn-Fe catalyst exhibited the best low-temperature activity, and more than 80 % NO x conversion in a reaction temperature range of 150−200 °C. and the ternary oxide catalysts Mn-Fe-Ce (0.1) prepared on this basis can reach about 95 % NO x conversion and excellent the tolerance of SO 2 and H 2 O at the same condition. The activity test results indicate that Ce-modification has a clear promoting effects on low temperature activity and resistance to SO 2 and/or H 2 O of the Mn-Fe catalyst. The effect of element doping on physiochemical properties of catalyst were investigated by XRD, BET, XPS, NH 3 -TPD and H 2 -TPR. The results show that there is a strong interaction between Ce, Co or Ni and Mn, Fe oxides, resulting in high dispersibility and reduced crystallinity of these oxides. In addition, the results always prove doping Ce could not only prominently modify and optimize the structure of mixed metal oxides, but also increase the relative content of Mn4+, Mn3+, Fe3+ and surface oxygen (O α) of Mn-Fe catalyst. Moreover, The specific surface area of the catalyst was increased and its surface acidity was strengthened after Ce doping, which is beneficial to increase the adsorption of NH 3. Finally, The typical Eley-Rideal mechanism over Mn-Fe-Ce (0.1) were proposed via the in situ DRIFTs experiments. [ABSTRACT FROM AUTHOR]

• Low-dimensional multi-oxides nanosheet were synthesized successfully by one-step synthesis. • Co-Mn-SnO 2 solid solution promoted the efficient electron interaction for catalysis. • Increased adsorbed oxygen, Mn3++Mn4+, Sn4+ and more acidity on Lewis acid sites were obtained. • E-R and l -H mechanisms co-existed on Co-Mn-SnO 2 surface in SCR reaction process. • L-NH 3 species and bidntate nitrate were the main active species at high temperatures. NH 3 -SCR performances were explored to the relationship between structure morphology and physio-chemical properties over low-dimensional ternary Mn-based catalysts prepared by one-step synthesis method. Due to its strong oxidation performance, Sn-MnOx was prone to side reactions between NO, NH 3 and O 2 , resulting in the generation of more NO 2 and N 2 O, here most of N 2 O was driven from the non-selective oxidation of NH 3 , while a small part generated from the side reaction between NH 3 and NO 2. Co or Ni doping into Sn-MnOx as solid solution components obviously stronged the electronic interaction for actively mobilization and weakened the oxidation performance for signally reducing the selective tendency of side reactions to N 2 O. The optimal modification resulted in improving the surface area and enhancing the strong interaction between polyvalent cations in Co/Ni-Mn-SnO 2 to provide more surface adsorbed oxygen, active sites of Mn3+ and Mn4+, high-content Sn4+ and plentiful Lewis-acidity for more active intermediates, which significantly broadened the activity window of Sn-MnOx, improved the N 2 selectivity by inhibiting N 2 O formation, and also contributed to an acceptable resistances to water and sulfur. At low reaction temperatures, the SCR reactions over three catalysts mainly obeyed the typical Elye-rideal (E-R) routs via the reactions of adsorbed l -NH x (x = 3, 2, 1) and B-NH 4 + with the gaseous NO to generate N 2 but also N 2 O by-products. Except for the above basic E-R reactions, as increasing the reaction temperature, the main adsorbed NO x -species were bidentate nitrates that were also active in the Langmuir-Hinshelwood reactions with adsorbed l -NH x species over Co/Ni modified Mn-SnO 2 catalyst. Probable surface SCR reaction pathways over Ni/Co-modified Mn-SnO 2 were put forward to follow the basic Elye-Rideal reactions between gaseous NO with adsorbed l -NH x on Lewis acid sites at low temperature while also obey the Langmuir-Hinshelwood routes of main active bidentate nitrates with l -NHx as increasing the reaction temperature. [Display omitted] [ABSTRACT FROM AUTHOR]

• CoMn 2 O 4 /TiO 2 catalysts modified with metals were prepared by sol–gel method. • CoMn 2 O 4 /W-TiO 2 presented more than 95% NOx conversion with 10 vol% H 2 O at 150–250 °C. • H 2 O played a promoting role in SCR activity and N 2 selectivity on CoMn 2 O 4 /W-TiO 2. • New lewis and Brønsted acid sites were created by H 2 O, enhancing NH 3 adsorption. • E-R mechanism was dominating pathway and promoted in the presence of H 2 O. Improving the resistance to H 2 O is crucial to promote industrial applications of Mn-based catalysts for selective catalytic reduction of NOx by NH 3 (NH 3 -SCR). In this work, we reported the CoMn 2 O 4 /TiO 2 catalyst, and W was introduced as a promoter to enhance the resistance to H 2 O at low-temperature. CoMn 2 O 4 /W-TiO 2 catalyst exhibited remarkable H 2 O-resistance of above 95% NOx conversion and nearly 100% N 2 selectivity at 150–250 °C in the presence of 10 vol% H 2 O. Further, the role of tungsten and the effect of water on the structure and chemical properties of CoMn 2 O 4 /W-TiO 2 catalyst were revealed by various techniques of BET, XRD, Raman, H 2 -TPR, NH 3 -TPD, XPS and in-situ DRIFTS experiments. The superior performance was attributed to unique spinel structure, mesoporous structure, highly dispersed tungsten species, greater surface acidity. The electron cycle among Mn, Co, W and Ti was beneficial to maintain the Mn3+/Mn4+ and Co3+ at high concentrations and enhance lattice oxygen mobility. The SCR reaction mainly followed the Eley-Rideal (E-R) mechanism over two catalysts, but the poor water resistance of CoMn 2 O 4 /TiO 2 was attributed to the suppression of NH 3 activation and E-R mechanism, despite NH 3 adsorption was enhanced. Both Lewis and Brønsted acid sites were created by the incorporation of tungsten in the presence of H 2 O, and enhanced NH 3 adsorption, promoting E-R reaction pathway. Besides, N 2 selectivity was significantly enhanced by H 2 O, which could be due to a decrease in the redox activity of both catalysts. This study opens up a new avenue for designing efficient and environment-friendly NH 3 -SCR catalysts and looks promising for practical application. [ABSTRACT FROM AUTHOR]

The paper presented facile method for preparing Mn, Co-BTC (BTC ​= ​1,3,5-benzenetricarboxylic acid) derived catalyst with honeycomb structure through direct decomposition of Mn and Co based metal-organic framework (MOF) Mn, Co-BTC in air. Also, the correlation between catalytic performance of MOF (metal organic framework) derivatives for the selective catalytic reduction (SCR) of NO x with ammonia and annealing temperature have been investigated. The catalytic activity test results indicated that annealing temperature had the clear promoting effects on catalytic performance. The X-ray photoelectron spectroscopic (XPS), X-ray diffraction (XRD), Thermogravimetric (TG), Scanning electron microscopy (SEM), Temperature programmed reduction of H 2 (H 2 -TPR) and Fourier-transform infrared (FTIR) spectra were employed to characterize Mn, Co-BTC and its derived catalysts. Based on SEM, FTIR and XRD analytical results, Mn, Co-BTC with nanoneedle structure turned into (Co, Mn) (Co, Mn) 2 O 4 spinel compound with honeycomb structure accompanied by decomposition of organic linkers through direct annealing process. The XPS and H 2 -TPR results showed that Mn, Co-BTC-500 (Mn, Co-BTC annealed at 500 ​°C) had the greatest interaction between Mn and Co, resulting in high catalytic performance for NH 3 -SCR of NO x , which were consistent with catalytic performance test results. Finally, based on the in-situ DRIFT experiments, it was suggested that the SCR process of NO x with NH 3 over Mn, Co-BTC-500 followed both Langmuir–Hinshelwood (L–H) mechanism and Eley-Rideal (E-R) mechanism. Mn, Co-BTC-derived catalyst with honeycomb structure the outstanding synergistic catalytic effect between manganese and cobalt presents good catalytic performance and SO 2 resistant for NH 3 -SCR. [Display omitted] • Among Mn, Co-BTC-derived catalysts, Mn, Co-BTC-500 catalyst had the best catalytic performance. • The main reason for good catalytic performance was due to its honeycomb structure and strong interaction between Mn and Co. • The SCR process of NO x with NH 3 over Mn, Co-BTC-500 followed both Langmuir–Hinshelwood (L–H) mechanism and Eley-Rideal (E-R) mechanism. [ABSTRACT FROM AUTHOR]