Low-temperature selective catalytic reduction of NO with NH3 over an FeO x /β-MnO2 composite

A series of Fe-modified β-MnO₂ (FeO _x /β-MnO₂) composite catalysts were prepared by an impregnation method with β-MnO₂ and ferro nitrate as raw materials. The structures and properties of the composites were systematically characterized and analyzed by X-ray diffraction, N₂ adsorption-desorption, high-resolution electron microscopy, temperature-programmed reduction of H₂, temperature-programmed desorption of NH₃, and FTIR infrared spectroscopy. The deNO _x activity, water resistance, and sulfur resistance of the composite catalysts were evaluated in a thermally fixed catalytic reaction system. The results indicated that the FeO _x /β-MnO₂ composite (Fe/Mn molar ratio of 0.3 and calcination temperature of 450 °C) had higher catalytic activity and a wider reaction temperature window compared with β-MnO₂. The water resistance and sulfur resistance of the catalyst were enhanced. It reached 100% NO conversion efficiency with an initial NO concentration of 500 ppm, a gas hourly space velocity of 45 000 h^-1, and a reaction temperature of 175-325 °C. The appropriate Fe/Mn molar ratio sample had a synergistic effect, affecting the morphology, redox properties, and acidic sites, and helped to improve the low-temperature NH₃-SCR activity of the composite catalyst.

Study of the denitration performance of a ceramic filter using a manganese-based catalyst

A MnO _x /γ-Al₂O₃ catalyst was prepared by impregnation of manganese acetate and alumina. After optimizing the composition, it was loaded into a ceramic filter (CF) by a one-step coating method. The results show that MnO _x /γ-Al₂O₃ had the best denitration activity when the Mn loading was 4 wt% with a calcination temperature of 400 °C. The MnO _x /γ-Al₂O₃ catalyst ceramic filter (MA-CCF) was made by loading the CF twice with MnO _x /γ-Al₂O₃. When face velocity (FV) was 1 m min^-1, MA-CCF displayed more than 80% NO conversion at 125-375 °C and possessed a good resistance of H₂O and SO₂. The abundant surface adsorbed oxygen, dense membrane and high-density fiber structure on the outer layer of CF effectively protected the catalyst and could improve MA-CCF denitration activity. The multiple advantages of MA-CCF made it possible for good application prospects.

Self-Defense Effects of Ti-Modified Attapulgite for Alkali-Resistant NOx Catalytic Reduction

Nowadays, the serious deactivation of deNO_x catalysts caused by alkali metal poisoning was still a huge bottleneck in the practical application of selective catalytic reduction of NO_x with NH₃. Herein, alkali-resistant NO_x catalytic reduction over metal oxide catalysts using Ti-modified attapulgite (ATP) as supports has been originally demonstrated. The self-defense effects of Ti-modified ATP for alkali-resistant NO_x catalytic reduction have been clarified. Ti-modified ATP with self-defense ability was obtained by removing alkaline metal cation impurities in the natural ATP materials without destroying its initial layered-chain structure through the ion-exchange procedure, accompanied with an obvious enrichment of Brønsted acid and Lewis acid sites. The self-defense effects embodied that both ion-exchanged Ti octahedral centers and abundant Si-OH sites in the Ti-ion-exchange-modified ATP could effectively anchor alkali metals via coordinate bonding or ion-exchange process, which induced alkali metals to be immobilized by the Ti-ion-exchange-modified ATP carrier rather than impair active species. Under this special protection of self-defense effects, Ti-ion-exchange-modified ATP supported catalysts still retained plentiful acidic sites and superior redox ability even after alkali metal poisoning, giving rise to the maintenance of sufficient NH_x and NO_x adsorption and the subsequent efficient reaction, which in turn resulted in high NO_x catalytic reduction capacity of the catalyst. The strategy provided new inspiration for the development of novel and efficient selective catalytic reduction of NO_x with NH₃ (NH₃-SCR) catalysts with high alkali resistance.

Recent progress of low-temperature selective catalytic reduction of NOx with NH3 over manganese oxide-based catalysts

Selective catalytic reduction with NH3 (NH3−SCR) was the most efficient approach to mitigate the emission of nitrogen oxides (NOx). Although the conventional manganese oxide-based catalyst had gradually become a kind...

Adjustment of operation temperature window of Mn-Ce oxide catalyst for the selective catalytic reduction of NOx with NH3

In order to enhance the catalytic activity of Mn-Ce oxide catalyst for the selective catalytic reduction of NO_x with NH₃ (NH₃-SCR), W was introduced as a promoter. With the doping of W, the NO_x conversion over Mn₃CeO_x catalyst above 150 °C was increased, and the N₂O production was significantly decreased. Even in the present of water vapour, Mn₃CeW_0.3O_x still showed a good SCR activity. H₂-TPR and XPS results suggested that the doping of tungsten could inhibit the charge imbalance and reducibility, which would inhibit NO oxidation to NO₂ over Mn₃CeO_x. As a result, the NO_x conversion below 150 °C over Mn₃CeW_0.3O_x was slightly lower than that over Mn₃CeO_x. Since the NO_x production and the NH₃ conversion during the NH₃ oxidation of Mn₃CeO_x were inhibited after the doping of W, the NO_x conversion above 150 °C over Mn₃CeW_0.3O_x was higher than that over Mn₃CeO_x. The transient reaction demonstrated that the doped W species on Mn₃CeW_0.3O_x could inhibit the N₂O produced by the Langmuir-Hinshelwood mechanism. Kinetic study proved that ν_SCR over Mn₃CeW_0.3O_x was obviously higher that over Mn₃CeO_x, ν_NSCR and ν_C-O over Mn₃CeO_x were much higher than those of Mn₃CeW_0.3O_x, which were consistent with the SCR activity.

MnO2 -Based Materials for Environmental Applications

Manganese dioxide (MnO₂ ) is a promising photo-thermo-electric-responsive semiconductor material for environmental applications, owing to its various favorable properties. However, the unsatisfactory environmental purification efficiency of this material has limited its further applications. Fortunately, in the last few years, significant efforts have been undertaken for improving the environmental purification efficiency of this material and understanding its underlying mechanism. Here, the aim is to summarize the recent experimental and computational research progress in the modification of MnO₂ single species by morphology control, structure construction, facet engineering, and element doping. Moreover, the design and fabrication of MnO₂ -based composites via the construction of homojunctions and MnO₂ /semiconductor/conductor binary/ternary heterojunctions is discussed. Their applications in environmental purification systems, either as an adsorbent material for removing heavy metals, dyes, and microwave (MW) pollution, or as a thermal catalyst, photocatalyst, and electrocatalyst for the degradation of pollutants (water and gas, organic and inorganic) are also highlighted. Finally, the research gaps are summarized and a perspective on the challenges and the direction of future research in nanostructured MnO₂ -based materials in the field of environmental applications is presented. Therefore, basic guidance for rational design and fabrication of high-efficiency MnO₂ -based materials for comprehensive environmental applications is provided.

MnOx–CeO2@TiO2 core–shell composites for low temperature SCR of NOx

The MnO_x–CeO₂@TiO₂ catalyst presents excellent NH₃-SCR activity and the TiO₂ shell is responsible for the good SO₂ tolerance.