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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]

Metal–organic framework (MOF) materials have attracted much attention as catalysts because of their high surface area, controllable pore size and desirable chemical functionalities. Hence, the fields of energy storage, sensing, gas storage, adsorption and catalysis have found substantial applications of MOF composites. Only a few researchers have conducted limited studies on the application of MOFs in the selective catalytic reduction of NOx with NH3 (NH3-SCR). This review article aims to provide accurate information on the application of MOFs and their derivatives in the selective catalytic reduction of NOx with NH3. The following areas have been briefly reviewed: (1) the morphology, structure, metal ions, ligands, and pore characteristics of MOFs affect their catalyst performance for the NH3-SCR, and these can be controlled by adjusting the pH, reaction time, reaction temperature, solvent and metal ion concentration. (2) MOF catalysts show notable SCR performance at low temperatures. The resistance to SO2 poisoning of bimetallic MOFs is higher than that of single-metal MOFs. The water resistance of MOFs for NH3-SCR performance can be improved by introducing the appropriate hydrophobic group and layer. (3) In order to overcome the limitations of MOF materials with low thermal stability, it is required to manufacture derivatives that maintain the structure and properties of MOFs. (4) There is an urgent need for research to reveal the difference in the interfacial chemistry process of SCR de-NOx over ordinary catalysts and MOF materials. We hope this review will help researchers understand more about the research progress of MOFs in the NH3-SCR process. (5) An in-depth study on the synthesis of MOF derivatives according to the confinement–pyrolysis–oxidation strategy should be conducted to synthesize MOF derivatives with high activity even at high GHSV and open the prospect of the industrial application of MOF materials. [ABSTRACT FROM AUTHOR]

[Display omitted] Improving the SO 2 resistance of catalysts is crucial to driving commercial applications of Mn-based catalysts. In this work, the phosphotungstic acid (HPW) modification strategy was applied to improve the N 2 selectivity, SO 2 and H 2 O resistance of the Mn-Ce-Co catalyst, and further, the mechanism of HWP modification on enhanced catalytic performance was explored. The results showed that HPW-Mn-Ce-Co catalyst exhibits higher NO x conversion (~100% at 100–250 °C) and N 2 selectivity (exceed 80% at 50–350 °C) due to more oxygen vacancies, greater surface acidity, and lower redox capacity. In situ diffused reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) reveal that HPW changed the reaction path of Mn-Ce-Co catalysts, promoted the adsorption and activation of NH 3 , and reduced the effect of SO 2 on the active bidentate nitrate species, and thereby exhibiting good SO 2 resistance. X-ray photoelectron spectrometer (XPS) and NH 3 temperature-programmed desorption of (NH 3 -TPD) results show that HPW can inhibit the formation of metal sulfate, and SO 2 can be combined with Ce species more easily. The generated Ce 2 (SO 3) 3 can not only protect Mn species but also increase the acid sites and weaken the poisoning effect of metal sulfate. This study provides a simple design strategy for the catalyst to improve the low-temperature catalytic performance and toxicity resistance. [ABSTRACT FROM AUTHOR]

BACKGROUND: Nitrogen oxide (NOx) is one of the important atmospheric pollutants, causing damage to the environment and the human body. Currently, selective catalytic reduction (SCR) technology is the main denitration method, and SCR catalyst is the key to this technology. Iron (Fe)‐based catalysts have recently been widely studied because of their low cost and good catalytic effect on medium and low temperature effects. In this article, iron‐cerium mixed oxide (FeOx‐CeO2) catalysts were prepared by five common preparation methods, and their physicochemical properties and low temperature NH3‐SCR catalytic activity were studied. RESULTS: The results show that the preparation method has a certain influence on the catalytic performance [activity and nitrogen (N2) selectivity] of the catalyst. The order of activity is microemulsion method (MM) ≈ sol–gel (SG) method > coprecipitation method > hydrothermal synthesis method > solid‐phase mixing (SPM) method. CONCLUSION: This result is related to the specific surface area of the catalyst, the microstructure, the valence distribution of the elements, the redox ability and the surface acidic sites. It is worth noting that the activity of the catalyst prepared by the SG method is good, but the selectivity of N2 is poor, which is related to the oxidizing ability of the catalyst. The catalyst prepared by the MM has moderate oxidizing ability and large specific surface area, provides abundant acidic sites and has excellent catalytic performance. © 2019 Society of Chemical Industry [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]

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]

Metal–organic framework (MOF) materials have attracted much attention as catalysts because of their high surface area, controllable pore size and desirable chemical functionalities. Hence, the fields of energy storage, sensing, gas storage, adsorption and catalysis have found substantial applications of MOF composites. Only a few researchers have conducted limited studies on the application of MOFs in the selective catalytic reduction of NOx with NH3 (NH3-SCR). This review article aims to provide accurate information on the application of MOFs and their derivatives in the selective catalytic reduction of NOx with NH3. The following areas have been briefly reviewed: (1) the morphology, structure, metal ions, ligands, and pore characteristics of MOFs affect their catalyst performance for the NH3-SCR, and these can be controlled by adjusting the pH, reaction time, reaction temperature, solvent and metal ion concentration. (2) MOF catalysts show notable SCR performance at low temperatures. The resistance to SO2 poisoning of bimetallic MOFs is higher than that of single-metal MOFs. The water resistance of MOFs for NH3-SCR performance can be improved by introducing the appropriate hydrophobic group and layer. (3) In order to overcome the limitations of MOF materials with low thermal stability, it is required to manufacture derivatives that maintain the structure and properties of MOFs. (4) There is an urgent need for research to reveal the difference in the interfacial chemistry process of SCR de-NOx over ordinary catalysts and MOF materials. We hope this review will help researchers understand more about the research progress of MOFs in the NH3-SCR process. (5) An in-depth study on the synthesis of MOF derivatives according to the confinement–pyrolysis–oxidation strategy should be conducted to synthesize MOF derivatives with high activity even at high GHSV and open the prospect of the industrial application of MOF materials. [ABSTRACT FROM AUTHOR]

Developing effective and stable catalysts for low-temperature selective catalytic reduction (SCR) of NO x remains challenging. Herein, we constructed a hierarchical structure by loading CoMn 2 O 4 onto Ti-doped CeO 2 , that CoMn 2 O 4 /CeTiO x catalyst has shown superior deNO x activity (>95% at 100–225 °C), prominent reaction activation energy (28.8 ± 0.9 kJ mol−1) and outstanding stability (>75% at 100–200 °C within H 2 O and SO 2). The "low-temperature active sites" and "dual anti-poisoning sites" contribute to excellent activity and stability. Firstly, the hierarchical structure boosts generation of active metal-support interface, which is conducive to oxygen migration (including adsorbed oxygen (O ads), lattice oxygen (O lat) and oxygen vacancy (O v)) and metal charge transfer (Mn2+/3++Ce4+↔Mn3+/4++Ce3+, Ti4++Ce3+↔Ce4++Ti3+). This is the key to breaking through the limits of catalytic activity stability. Secondly, enhanced surface acidity favors NH 3 adsorption and activation, which accelerates -NH 2 /-NH concatenate with NO x through Eley-Rideal mechanism to generate N 2 and H 2 O. Thirdly, the dual strong SO 2 affinity sites by Ti-induced CeO 2 crystal reconstruction retard the active center affected by the sulfate species, which contributes to striking stability. This work highlights the importance of design of isolated active sites to improve SO 2 and H 2 O endurance. [Display omitted] • The CoMn 2 O 4 /CeTiOx catalyst exhibited excellent low-temperature SCR performance. • The CoMn 2 O 4 /CeTiOx catalyst took on a superior endurance to water and sulfur volatility at low-temperature. • The existence of cooperative interface of metal-support promotes electron cycling and reaction gas adsorption activation. • The supported catalysts were dominated by Eley-Rideal mechanism which was less effected by SO 2. • The presence of dual sacrifice sites delayed the deactivation of low-temperature active components. [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]