Effects of manganese content and calcination temperature on Mn/Zr-PILM catalyst for low-temperature selective catalytic reduction of NOx by NH3 in metallurgical sintering flue gas

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.

Highly stable and efficient calcined γ-Al2O3 catalysts loaded with MnOx-CeOx for the ozonation of oxytetracycline

Catalytic ozonation with supported metal oxides is a promising strategy for addressing refractory pollutants in wastewater. In this study, γ-Al2O3 supported MnOx-CeOx catalysts (MC1, MC2, and MC3) obtained at different calcination temperatures (400 °C, 550 °C, and 700 °C) were applied as effective catalysts for ozonation and explored the feasibility of the treatment of oxytetracycline (OTC) wastewater. Comparatively, the MC2 possessed the highest molar ratios of Mn3+/Mn4+ (1.60) and Ce3+/Ce4+ (0.96), the largest surface area (273.8 m2 g-1) with a petal-shaped structure, and most abundant surface hydroxyls (3.78 mmol g-1). These physicochemical characteristics benefited the surface reaction and resulted in the acceleration of ozone decomposition, electron transfer, and •OH generation, thereby improving the catalyst's adsorption ability and catalytic activity. The combination with MC2 increased the OTC and COD removal of the ozonation process from 59.1% and 29.0% to 94.7% and 83.3% in 25 min, respectively. By employing electron paramagnetic resonance (EPR) and radical quenching experiments, it was verified that •OH species generation promoted the mineralization of OTC. The possible degradation pathways of OTC were investigated through mass spectrometry, and the route consisted of dehydration, deamination, and demethylation. Moreover, during a 12-day continuous experiment, MC2 catalyst exhibited excellent reusability and catalytic stability, with COD removal efficiencies above 80%.

Optimized Synthesis Routes of MnOx-ZrO2 Hybrid Catalysts for Improved Toluene Combustion

In this contribution, the three Mn-Zr catalysts with MnxZr1−xO2 hybrid phase were synthesized by two-step precipitation route (TP), conventional coprecipitation method (CP) and ball milling process (MP). The components, textural and redox properties of the Mn-Zr hybrid catalysts were studied via XRD, BET, XPS, HR-TEM, H2-TPR. Regarding the variation of synthesis routes, the TP and CP routes offer a more obvious advantage in the adjustment of the concentration of MnxZr1−xO2 solid solution compared to the MP process, which directly commands the content of Mn4+ and oxygen vacancy and lattice oxygen, and thereby leads to the enhanced mobility of reactive oxygen species and catalytic activity for toluene combustion. Moreover, the TP-Mn2Zr3 catalyst with the enriched exposure content of 51.4% for the defective (111) lattice plane of MnxZr1−xO2 exhibited higher catalytic activity and thermal stability for toluene oxidation than that of the CP-Mn2Zr3 sample with a value of 49.3%. This new observation will provide a new perspective on the design of bimetal catalysts with a higher VOCs combustion abatement.

Effects of ferric and manganese precursors on catalytic activity of Fe-Mn/TiO2 catalysts for selective reduction of NO with ammonia at low temperature

Fe-Mn/TiO₂ catalysts were prepared through the wet impregnation process to selective catalytic reduction of NO by NH₃ at low temperature, and series of experiments were conducted to investigate the effects of key precursors on their SCR performance. Ferric nitrate, ferrous sulfate, and ferrous chloride were chosen as Fe precursors while manganese nitrate, manganese acetate, and manganese chloride as Mn precursors. These precursors had been commonly used to prepare Fe-Mn/TiO₂ catalysts by numerous researchers. The results showed that there were distinct differences in NO conversion efficiencies at low temperature of catalysts prepared with different precursors. Catalysts prepared with ferric nitrate and manganese nitrate precursors exhibited the best catalytic performance at low temperature, while three kinds of catalysts prepared with manganese chloride precursors exhibited significantly low catalytic activity. All catalysts were characterized by XRD, SEM, H₂-TPR, NH₃-TPD, and XPS. The results indicated that when the catalysts were prepared with manganese nitrate or manganese acetate as precursors, Mn⁴⁺ contents and O_β/(O_β + O_α) ratios decreased in an order of ferric nitrate > ferrous sulfate > ferrous chloride, which was consistent with the change of catalytic activities of the corresponding catalysts at low temperature. It can be found that the excellent catalytic performance of Fe(A)-Mn(a)/TiO₂ was ascribed to high redox property and enrichment of Mn⁴⁺species and surface chemical labile oxygen groups.

Optimizing reaction conditions and experimental studies of selective catalytic reduction of NO by CO over supported SBA-15 catalyst

Selective catalytic reduction of NO with CO (CO-SCR) was investigated based on optimizing the operating conditions by response surface methodology (RSM) and by appropriately choosing the supported SBA-15 catalysts. The effects of the CO-SCR reaction parameters such as NO:CO molar ratios and oxygen concentrations on the catalytic performance were determined by RSM to evaluate the NO conversion using a first-order polynomial model. The CuO/SBA-15 and Fe₂O₃/SBA-15 catalysts were synthesized by a hydrothermal method and characterized by X-ray diffraction (XRD), atomic absorption spectroscopy (AAS), N₂ adsorption-desorption (BET), scanning electron microscopy coupled to energy dispersive X-Ray spectroscopy (SEM-EDS), and Fourier transform infrared spectroscopy (FTIR) to investigate the physicochemical properties of the solids. The RSM showed a very good agreement between predicted values and experimental results with the Pareto analysis confirming the accuracy and reliability of the model. The optimized results indicated the maximum NO conversion at 500 °C with using the NO to CO molar ratio of 1:2 (500:1000 ppm) in the absence of oxygen. Under these conditions, CuO/SBA-15 catalyst achieved 99.7% of NO conversion, whereas Fe₂O₃/SBA-15 had 98.1% of the catalytic parameter. Catalytic tests in CO-SCR reaction were performed on both catalysts at optimum operating conditions with CuO/SBA-15 exhibiting better performance compared to that of Fe₂O₃/SBA-15. The results revealed that CuO/SBA-15 was a promising catalyst for CO-SCR of NO due to the well-dispersed CuO phase on SBA-15 surface that allows the solid being more tolerant to the presence of oxygen.