以尿素为沉淀剂,分别用水热法和均相沉淀法制备了一系列Cu-Mn-O氧化物催化剂,并对催化剂进行了BET,XRD,XPS和FT-IR等表征,考察了Cu-Mn-O催化剂在无氧条件下对丙烷还原去除NO的催化反应性能.结果表明,Cu-Mn-O体系的物相组成与制备方法和焙烧温度有关,并影响丙烷还原NO反应的催化性能.当焙烧温度在500～600℃时,水热法制备的样品中的主要物相是Cu1.5Mn1.5O4和CuMn2O4;而尿素均相沉淀法样品中的主要物相为类尖晶石Cu1.5Mn1.5O4;当焙烧温度在700～900℃时,水热法样品中的主相为尖晶石CuMn2O4,而均相沉淀法中仍是Cu1.5Mn1.5O4相.因此,对水热法而言,当焙烧温度由600℃增加到700℃时,发生了Cu1.5Mn1.5O4到CuMn2O4的相变,这一相变不仅影响晶粒度和比表面积,并提高了丙烷还原NO反应的催化活性.根据XRD,XPS的实验结果和尖晶石结构的特征,得到了详细的Cu1.5Mn1.5O4和CuMn2O4的结构式,并根据得到的结构式在一定深度上解释了二者催化性能的差别.XRD结果显示在无氧条件下进行丙烷还原NO反应后,反应温度为600℃时,催化剂中的主相尖晶石结构遭到破坏,分解为MnO,CuO和Cu的混合物.这些由尖晶石分解而成的混合物在无氧条件下仍对催化反应有优异的催化活性(NO转化率达到40%).在本工作中,用FT-IR表征了反应后的催化剂表面,发现了大量的NO2吸附物种和少量的NO3吸附物种.这是C3H8还原NO反应的中间产物,从而进一步为"协同反应机理"提供了依据.%A series of Cu-Mn-O oxides were prepared by homogeneous precipitation (labeled as U) and hydrothermal method (labeled as H), respectively. The catalysts have been characterized by means of XRD, BET, XPS, and FT-IR analyses. The activity of the catalysts for the reduction of NO with propane was evaluated. The results indicate that the composition of Cu-Mn-O system had dependence on preparation method and calcination temperature, which influenced the catalytic performance for the reduction of NO by propane. In the case of sample from hydrothermal method, Cu1.5Mn1.5O4 and CuMn204 were predominant phases with the calcination temperature at range of 500～600 ℃. Then the Cu1.5Mn1.5O4 disappeared as calcination temperature above 700 ℃. As for the samples prepared by urea homogeneous precipitation method, Cu1.5Mn1.5O4 was main phase in all these samples calcined above 500 C. Therefore, for hydrothermal method, a phase transition from Cu1.5Mn1.5O4 to CuMn204 occurred with the calcination temperature increasing from 600 to 700 ℃. This phase transition not only affected the grain size and specific surface area but also enhanced the catalytic activity in the reduction of NO by C3H8. According to the results of XRD, XPS and the structural character of spinel, the detailed structure formulas for Cu1.5Mn1.504 and CuMn2O4 were obtained respectively, and by which the difference of catalytic performance of both spinels could be explained to a certain degree. XRD results demonstrated that the spinel structure of catalysts collapsed with appearance of MnO, CuO and Cu after reaction run over temperature of 600 ~C. It was so surprised that these mixed material possessed good activity for reaction, even higher than the fresh catalysts H-CuMn-700 and U-CuMn-700 in catalytic performance. Furthermore, according to FT-IR spectra, a great deal of (NO2)ad. and small amounts of (NO3)ad adsorbates, that were considered as intermediates, were observed over the catalysts after reaction. This result was in fair agreement with the “synergetic reaction mechanism”.
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