不同晶型和形貌二氧化锰的可控合成及其催化性能

Controllable Synthesis of Manganese Oxides with Different Crystalline Structure and Morphology and Their Catalytic Activities

摘要:

以Mn(NO3)2为锰源，(NH4)2S2O8为氧化剂，通过控制水热反应条件，可控合成了2种晶型和不同形貌的MnO2。运用X射线衍射、扫描电镜、透射电镜和程序升温还原等方法对制备的氧化锰进行了表征，并以二甲醚的催化燃烧为探针反应考察了2种晶型二氧化锰的催化活性。研究结果表明，反应物浓度和水热温度主要影响MnO2的形貌。在硝酸锰浓度达到0.2 mol/L时，α-MnO2形貌由棒状转变成海胆状；在(NH4)2S2O8浓度超过0.1 mol/L时，有助于形成均一的海胆。硫酸主要影响MnO2的晶型，当在反应体系中加入1mL浓硫酸（硫酸浓度达到0.61 mol/L）时，会使MnO2从γ相向α相转变。相比于α-MnO2，海胆状γ-MnO2在二甲醚燃烧反应中表现出更优异的催化性能(T10为145℃、T90为236℃)。

Abstract:

Two types of manganese dioxides with various morphology are prepared by hydrothermal method based on the redox reaction between Mn(NO3)2 and (NH4)2S2O8 under different hydrothermal conditions. The prepared MnO2 are characterized by XRD, SEM, TEM and H2-TPR techniques, and tested for the catalytic combustion of dimethyl ether(DME). The results show that the concentration of reactants and the reaction temperature mainly influence the morphology of MnO2. With the concentration of Mn(NO3)2 rise to 0.2 mol/L, the shape of α-MnO2 change from nanorod to urchin; Improving the concentration of (NH4)2S2O8 above 0.1 mol/L favors for the formation of uniform urchin shape of α-MnO2; The sulfur acid affect greatly the crystal structure of MnO2 , and enhancing the concentration over 0.61 mol/L can make the MnO2 evolving from γ phase to α phase. Compared with α-MnO2, the urchin-like γ-MnO2 displays better activity in the DME combustion reaction with a T10 of 145℃ and a T90 of 236℃, which is related with the H2-TPR result.