Insights into the co-doping effect of Fe3+ and Zr4+ on the anti-K performance of CeTiOx catalyst for NH3-SCR reaction

Single stranded 1D-helical Cu coordination polymer for ultra-sensitive ammonia sensing at room temperature

With the increasing demand for ammonia applications, there is a significant focus on improving NH3 detection performance at room temperature. In this study, we introduce a groundbreaking NH3 gas sensor based on Cu(I)-based coordination polymers, featuring semiconducting, single stranded 1D-helical nanowires constructed from Cu-Cl and N-methylthiourea (MTCP). The MTCP demonstrates an exceptional response to NH3 gas (>900% at 100 ppm) and superior selectivity at room temperature compared to current materials. The interaction mechanism between NH3 and the MTCP sensor is elucidated through a combination of empirical results and computational calculations, leveraging a crystal-determined structure. This reveals the formation of NH3-Cu and NH3-H3C complexes, indicative of a thermodynamically favorable reaction. Additionally, Ag-doped MTCP exhibits higher selectivity and a response over two times greater than the original MTCP, establishing it as a prominent NH3 detection system at room temperature.

Promotional effects of Nb5+ and Fe3+ co-doping on catalytic performance and SO2 resistance of MnOx-CeO2 low-temperature denitration catalyst

As we know, SO₂ can cause MnO_x-CeO₂ (MnCeO_x) catalyst poisoning, which seriously shortens the service life of the catalyst. Therefore, to enhance the catalytic activity and SO₂ tolerance of MnCeO_x catalyst, we modified it by Nb⁵⁺ and Fe³⁺ co-doping. And the physical and chemical properties were characterized. These results illustrate that the Nb⁵⁺ and Fe³⁺ co-doping can optimally improve the denitration activity and N₂ selectivity of MnCeO_x catalyst at low temperature by improving its surface acidity, surface adsorbed oxygen as well as electronic interaction. What's more, NbO_x-FeO_x-MnO_x-CeO₂ (NbFeMnCeO_x) catalyst possesses an excellent SO₂ resistance due to less SO₂ being adsorbed and the ammonium bisulfate (ABS) formed on its surface tends to decompose, as well as fewer sulfate species formed on its surface. Finally, the possible mechanism that Nb⁵⁺ and Fe³⁺ co-doping enhances the SO₂ poisoning resistance of MnCeO_x catalyst is proposed.

Low-Temperature NH3-SCR Performance and In Situ DRIFTS Study on Zeolite X-Supported Different Crystal Phases of MnO2 Catalysts

In this study, a series of zeolite-X-supported different crystal phases of MnO2 (α-MnO2, β-MnO2, γ-MnO2, and σ-MnO2) catalysts were prepared via a solid-state diffusion method and high-heat treatment method to explore their low-temperature NH3-SCR performance. All of the catalysts featured typical octahedral zeolite X structures and manganese dioxides species of various crystal types dispersed across the support surface. Throughout the entire temperature range of the reaction, γ-MnO2/X catalyst had the highest NO conversion. Additionally, β-MnO2/X, γ-MnO2/X, and σ-MnO2/X catalysts had nearly 100% of N2 selectivity, whereas the α-MnO2/X catalyst had the lowest N2 selectivity (about 90%) below 125 °C. Moreover, the γ-MnO2/X catalyst demonstrated superior acidity capacity and reduction ability compared with the other three catalysts. All the catalysts contained the essential intermediates NH2NO and NH4NO3 species, which are essential to the SCR reaction. More acid sites and nitrate species existed on the γ-MnO2/X catalyst than on the other catalysts, thereby boosting the SCR reaction.

NO Reduction Reaction by Kiwi Biochar-Modified MnO2 Denitrification Catalyst: Redox Cycle and Reaction Process

NO is a major environmental pollutant. MnO2 is often used as a denitrification catalyst with poor N2 selectivity and weak SO2 resistance. Kiwi twig biochar was chosen to modify MnO2 samples by using the hydrothermal method. The NO conversion rates of the biochar-modified samples were >90% at 125–225 °C. Kiwi twig biochar made the C2MnO2 sample with a larger specific surface area, a higher number of acidic sites and Oβ/Oα molar ratio, leading to more favorable activity at high temperatures and better SO2 resistance. Moreover, the inhibition of the NH3 oxidation reaction and the Mn3+ → Mn4+ process played a crucial role in the redox cycle. What was more, Brønsted acidic sites present on the C1MnO2 sample participate in the reaction more rapidly. This study identified the role of biochar in the reaction process and provides a reference for the wide application of biochar.

Effect of Bimetal Element Doping on the Low-Temperature Activity of Manganese-Based Catalysts for NH3-SCR

A series of novel Mn₆Zr_1-xCo_x denitrification catalysts were prepared by the co-precipitation method. The effect of co-modification of MnO_x catalyst by zirconium and cobalt on the performance of NH₃-SCR was studied by doping transition metal cobalt into the Mn₆Zr₁ catalyst. The ternary oxide catalyst Mn₆Zr_0.3Co_0.7 can reach about 90% of NO_x conversion in a reaction temperature range of 100–275°C, and the best NO_x conversion can reach up to 99%. In addition, the sulfur resistance and water resistance of the Mn₆Zr_0.3Co_0.7 catalyst were also tested. When the concentration of SO₂ is 200ppm, the NO_x conversion of catalyst Mn₆Zr_0.3Co_0.7 is still above 90%. 5 Vol% H₂O has little effect on catalyst NO_x conversion. The results showed that the Mn₆Zr_0.3Co_0.7 catalyst has excellent resistance to sulfur and water. Meanwhile, the catalyst was systematically characterized. The results showed that the addition of zirconium and cobalt changes the surface morphology of the catalyst. The specific surface area, pore size, and volume of the catalyst were increased, and the reduction temperature of the catalyst was decreased. In conclusion, the doping of zirconium and cobalt successfully improves the NH₃-SCR activity of the catalyst.

Influence of phosphorus on the NH3-SCR performance of CeO2-TiO2 catalyst for NOx removal from co-incineration flue gas of domestic waste and municipal sludge

Domestic waste and municipal sludge are two major solid hazardous substances generated from human daily life. Co-incineration technology is regarded as an effective method for the treatment of them. However, the emitted NO_x-containing exhaust with high content of phosphorus should purified strictly. CeO₂-TiO₂ is a promising catalyst for removal of NO_x by NH₃-SCR technology, but the effect of phosphorous in the exhaust is ambiguous. Therefore, the effect of phosphorus on NH₃-SCR performance and physicochemical properties of CeO₂-TiO₂ catalyst was investigated in our present work. It was found that phosphorus decreased the NH₃-SCR activity below 300 °C. Interestingly, it suppressed the formation of NO_x and N₂O caused by NH₃ over-oxidation above 300 °C. The reason might be that phosphorus induced Ti⁴⁺ to migrate from CeO₂-TiO₂ solid solution and form crystalline TiO₂, which led to the destruction of Ti-O-Ce structure in the catalyst. So, the transfer of electrons between Ti and Ce ions, the relative contents of Ce³⁺, and surface adsorbed oxygen, as well as the redox performance were limited, which further inhibited the over-oxidation of NH₃. In addition, phosphorus weakened the NH₃ adsorption on Lewis acid sites and the adsorption performance of NO + O₂, while increased the Brønsted acid sites. Finally, the reaction mechanism over CeO₂-TiO₂ catalyst did not change after introducing phosphorus, L-H and E-R mechanisms co-existed on the surface of the catalysts.