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Reverse Micelle Strategy for the Synthesis of MnO _x -TiO₂ Active Catalysts for NH₃-Selective Catalytic Reduction of NO _x at Both Low Temperature and Low Mn Content.

ABSTRACT: MnO _x -TiO₂ catalysts (0, 1, 5, and 10 wt % Mn nominal content) for NH₃-SCR (selective catalytic reduction) of NO _x have been synthesized by the reverse micelle-assisted sol-gel procedure, with the aim of improving the dispersion of the active phase, usually poor when obtained by other synthesis methods (e.g., impregnation) and thereby lowering its amount. For comparison, a sample at nominal 10 wt % Mn was obtained by impregnation of the (undoped) TiO₂ sample. The catalysts were characterized by using an integrated multitechnique approach, encompassing X-ray diffraction followed by Rietveld refinement, micro-Raman spectroscopy, N₂ isotherm measurement at -196 °C, energy-dispersive X-ray analysis, diffuse reflectance UV-vis spectroscopy, temperature-programmed reduction technique, and X-ray photoelectron spectroscopy. The obtained results prove that the reverse micelle sol-gel approach allowed for enhancing the catalytic activity, in that the catalysts were active in a broad temperature range at a substantially low Mn loading, as compared to the impregnated catalyst. Particularly, the 5 wt % Mn catalyst showed the best NH₃-SCR activity in terms of both NO _x conversion (ca. 90%) and the amount of produced N₂O (ca. 50 ppm) in the 200-250 °C temperature range.

SUBMITTER: Bonelli B

PROVIDER: S-EPMC8482467 | biostudies-literature | 2021 Sep

REPOSITORIES: biostudies-literature

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Reverse Micelle Strategy for the Synthesis of MnO x -TiO2 Active Catalysts for NH3-Selective Catalytic Reduction of NO x at Both Low Temperature and Low Mn Content.

Bonelli Barbara B Tammaro Olimpia O Martinovic Ferenc F Nasi Roberto R Dell'Agli Gianfranco G Rivolo Paola P Giorgis Fabrizio F Ditaranto Nicoletta N Deorsola Fabio Alessandro FA Esposito Serena S

ACS omega 20210914 38

MnO x -TiO2 catalysts (0, 1, 5, and 10 wt % Mn nominal content) for NH3-SCR (selective catalytic reduction) of NO x have been synthesized by the reverse micelle-assisted sol-gel procedure, with the aim of improving the dispersion of the active phase, usually poor when obtained by other synthesis methods (e.g., impregnation) and thereby lowering its amount. For comparison, a sample at nominal 10 wt % Mn was obtained by impregnation of the ...[more]

PMID: 34604638

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Project description:The group has shown that Baiyun Ebo rare earth concentrate has excellent performance in NH3-SCR denitrification when used as a carrier, where rare earth elements are mainly present in cerium fluorocarbon ore (CeCO3F) and monazite (CePO4) mineral phases. In this paper, a new low-temperature NH3-SCR catalyst of Mn-Fe/CeCO3F-monazite was prepared by an impregnation method, using synthetic CeCO3F and purified monazite as carriers. By exploring its denitrification performance and mechanistic analysis, it provides theoretical guidance for the use of rare earth concentrates as low-temperature NH3-SCR catalysts. Our previous studies have determined the optimum loading of Fe, so this paper needs to be investigated for the optimum doping ratio of the active substance Mn. The results of the activity tests, XRD and BET have determined that the best denitrification rate and catalytic performance was achieved at a ratio of Mn : Ce of 1 : 5. The denitrification activity of the different catalysts was investigated by loading Fe, Mn and Fe and Mn together. The results obtained by means of experimental analyses such as XRD, SEM, BET and activity tests showed that the composite catalyst loaded with Fe and Mn at the same time, had the highest activity and its denitrification rate could reach 94.8% at 250 °C. This is mainly attributed to the fact that the interaction of Fe, Mn can promote the dispersion of each other on the carrier surface, which greatly improves the specific surface area of the catalyst. The introduction of Fe and Mn increases the acidic sites and the amount of acid on the catalyst surface, which results in the formation of a large number of oxygen vacancies and the presence of more oxygen species on the catalyst surface, which facilitate the migration of oxygen. The new catalyst was investigated by Fourier transform infrared (FTIR) spectroscopy to characterise the adsorption and transformation behaviour of the reactive species on the surface of the catalyst, and to investigate the reaction mechanism. The results showed that the entire reaction process followed the L-H mechanism, with the gaseous NO adsorption and activation on the catalyst surface generating bidentate nitrate, bridging nitrate species and NH3/NH4 + species as the main intermediate species involved in the reaction, both of which underwent redox reactions on the catalyst surface to produce N2 and H2O. The above results indicated that the CeCO3F-monazite carrier has excellent performance, and provided a theoretical basis for the high-value utilization of rare earth concentrates.

Dataset Information

Reverse Micelle Strategy for the Synthesis of MnO _x -TiO₂ Active Catalysts for NH₃-Selective Catalytic Reduction of NO _x at Both Low Temperature and Low Mn Content.

Publications

Reverse Micelle Strategy for the Synthesis of MnO <sub><i>x</i></sub> -TiO<sub>2</sub> Active Catalysts for NH<sub>3</sub>-Selective Catalytic Reduction of NO <sub><i>x</i></sub> at Both Low Temperature and Low Mn Content.

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