A γ-Fe2O3-modified nanoflower-MnO2/attapulgite catalyst for low temperature SCR of NOx with NH3

A novel mesoporous γ-Fe₂O₃-modified nanoflower-MnO₂/attapulgite catalyst has been fabricated through a facile hydrothermal method and used for low temperature SCR of NO_x with NH₃.

TiO2-SiO2 supported MnWO x catalysts by liquid-phase deposition for low-temperature NH3-SCR

NH3-SCR is an environmentally important reaction for the abatement of NO x from different resources. MnO2-based catalyst has attracted significant attention due to the excellent activity. In this paper, a series of MnWO x /TiO2-SiO2 catalysts were prepared by liquid-phase deposition method. The catalysts were characterized by N2 adsorption/desorption, XRD, TEM, XPS, FT-IR, H2-TPR, TG and water adsorption capacity. The existence of SiO2 improved the SO2 and H2O resistance of the MnWO x /TiO2-SiO2 catalyst without decreasing the NH3-SCR activity. Under the reaction conditions of 260°C and 60 000 ml gcata h-1 gas hourly space velocity (GHSV), the NO conversion was kept stable at about 95% for 140 min on stream. The excellent performance of MnWO x /TiO2-SiO2 catalyst is considered to be originated from the texture properties and active species dispersion improvement by SiO2 in the support and low-temperature preparation.

Environment-friendly magnetic Fe-Ce-W catalyst for the selective catalytic reduction of NO x with NH3: influence of citric acid content on its activity-structure relationship

The influence of the citric acid content on the structural and redox properties of a magnetic iron–cerium–tungsten mixed oxide catalyst prepared through a microwave-assisted citric acid sol–gel method is investigated via TG–DTG–DSC, XRD, N₂ adsorption–desorption, XPS, H₂-TPR and NH₃-TPD. Additionally, the NH₃-SCR activity of the magnetic FeCeW-m (m = 0.25, 0.5 and 1.0) catalysts are also studied. The results indicate that an increase in citric acid content strengthens the sol–gel reaction between citric acid and metal ions and promotes the formation of the γ-Fe₂O₃ crystallite not α-Fe₂O₃. Meanwhile, it decreases the BET surface area and pore volume of the catalyst. Furthermore, the surface concentration of iron species on the catalyst is enhanced when the molar ratio of citric acid/(Fe + Ce + W) increases from 0.25 to 1.0, but its surface absorbed oxygen and total oxygen concentration decrease. The magnetic FeCeW-0.5 catalyst shows the best reducibility at temperatures below 790 °C. The increase in the citric acid content inhibits the formation of acid sites in the catalyst, thus the magnetic FeCeW-0.25 catalyst possesses the most Lewis acid sites and Brønsted acid sites among the catalysts. The enhancement in citric acid content is beneficial to improve the SCR reaction rates normalized by the surface area of the catalyst. This catalyst exhibits high anti-SO₂ and H₂O poisoning, and the molar ratio of citric acid/(Fe + Ce + W) affects the adsorption of NO_x species on its surface.

The enhancement of critic acid amount strengthened the sol–gel reaction between critic acid and metal ions, showed an important role on the structure properties of magnetic Fe–Ce–W mixed oxide catalyst, thereby affected its NH₃-SCR activity.

Synthesis of Both Powdered and Preformed MnO x -CeO2-Al2O3 Catalysts by Self-Propagating High-Temperature Synthesis for the Selective Catalytic Reduction of NO x with NH3

MnO _x -CeO₂-Al₂O₃ powdered and preformed catalysts were prepared through self-propagating high-temperature synthesis (SHS) and impregnation methods. Compared to the traditional impregnation method, the SHS method has a shorter catalyst preparation cycle and simpler preparation process. The characterization results showed that mixed crystals of cerium, aluminum, and manganese oxides were formed through the SHS method, the binding energy of Mn⁴⁺ increased, and the active components were distributed uniformly. The MnO _x -CeO₂-Al₂O₃ powdered catalyst had an extensive pore structure, with a Brunauer-Emmett-Teller surface area of approximately 136 m²/g, a pore volume of approximately 0.17 cm³/g, and an average pore diameter of approximately 5.1 nm. Furthermore, the MnO _x -CeO₂-Al₂O₃ powdered catalyst achieved a NO _x conversion higher than 80% at 100-250 °C. Coating liquids with identical metal-ion concentrations were prepared using the catalysts, and the preformed catalyst obtained through the SHS method had a higher loading capacity after one coating. The MnO _x -CeO₂-Al₂O₃ preformed catalyst achieved a NO _x conversion higher than 70% at 200-350 °C.