不同晶体结构MnO2纳米催化剂低温NH3-SCR性能研究

为了探究催化剂的结构和催化活性的关系，采用水热法制备了四种不同晶体结构的MnO₂纳米催化剂（α-MnO₂、β-MnO₂、γ-MnO₂和δ-MnO₂），并考察了其低温NH₃-SCR活性。结果表明，不同晶体结构催化剂的活性不同，依次为γ-MnO₂ > α-MnO₂ > β-MnO₂ > δ-MnO₂，γ-MnO₂表现出最高的催化活性，NO_x转化率在150-260℃超过90%。随后，通过X射线衍射（XRD）、扫描电子显微镜（SEM）、N₂吸附-脱附、热重（TG）、红外光谱（FT-IR）、程序升温还原（H₂-TPR）及吡啶吸附红外光谱（Py-FTIR）等表征手段对催化剂的结构和性质进行分析。结果表明，α-MnO₂和β-MnO₂为纳米棒，γ-MnO₂和δ-MnO₂为纳米针，催化剂的比表面积并不是影响低温NH₃-SCR活性的主导因素。γ-MnO₂具有适宜的孔道结构、较强的氧化还原能力、丰富的化学氧含量和Lewis酸酸性位点，是其具有最高低温NH₃-SCR活性的原因。

Study on the performance of low temperature NH3-SCR over MnO2 nano-catalyst with different crystal structures

To investigate the relationship between the structure and catalytic activity, four types of MnO₂ nano-catalysts with various crystal structures (α-MnO₂, β-MnO₂, γ-MnO₂ and δ-MnO₂) were synthesized by hydrothermal method, and their low temperature NH₃-SCR activity were tested. The results indicated that catalysts with different structures showed various activities which followed the sequence of γ-MnO₂ > α-MnO₂ > β-MnO₂ > δ-MnO₂. It was found that γ-MnO₂ showed highest catalytic activity and its NO_x conversion rate surpassed 90% at the temperature range of 150-260℃. The catalysts were characterized by X-ray diffraction(XRD), scanning electron microscopy (SEM), N₂ adsorption-desorption, thermogravimetric(TG), infrared (FT-IR), temperature programmed reduction(H₂-TPR) and pyridine infrared spectroscopy (Py-FTIR). It was inferred that the morphology of the α-MnO₂ and β-MnO₂ were nanorods, while γ-MnO₂ and δ-MnO₂ with the structures of nanoneedles. The specific surface area of the catalyst was not the dominant factor affecting the NH₃-SCR activity at low temperature. The decent pore structure, strong redox property,abundant chemisorption oxygen and Lewis acid sites were responsible for high low temperature NH₃-SCR activity of γ-MnO₂ nano-catalyst.