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用沉淀法、浸渍法和机械混合物焙烧法制备了三组MoO_3-SnO_2催化剂。XDR,IR和ESR等研究表明:MoO_3-SnO_2之间存在明显的相互作用,两组份间发生电子迁移现象,导致Mo(Ⅵ)→Mo(Ⅴ)的价态变化,产生pKa≤+3.3的表面酸位和甲醇选择氧化活性位。制备方法对这种相互作用以及样品的催化性能有明显影响。沉淀法所得样品中MoO_3可溶于SnO_2形成固溶体;浸渍法则可发生钼离子向SnO_2体相的扩散;机械混合物焙烧法在一定MoO_3含量下,MoO_3可在SnO_2表面形成近似单层分散。红外光谱中950cm~(-1)的新吸收谱带可归因于表面上Mo(Ⅴ)=0振动。表面Mo(Ⅴ)位可能是催化剂表面酸位和甲醇氧化的活性中心。没有发现催化剂中Sn~(4+)价态有明显变化。
Three groups of MoO_3-SnO_2 catalysts were prepared by precipitation method, impregnation method and mechanical mixture roasting method. XDR, IR and ESR have shown that there is a clear interaction between MoO_3-SnO_2 and the phenomenon of electron transfer occurs between the two components, resulting in the valence change of Mo (Ⅵ) → Mo (Ⅴ) Surface acid sites and methanol selective oxidation activity. The preparation method has a significant effect on this interaction and on the catalytic performance of the sample. MoO 3 in the sample obtained by the precipitation method can be dissolved in SnO 2 to form a solid solution. The impregnation method can cause the diffusion of molybdenum ions into the SnO 2 phase. MoO 3 can form an almost monolayer dispersion on the surface of SnO 2 under certain MoO 3 content. The new absorption band of 950 cm -1 in IR spectra can be attributed to the Mo (Ⅴ) = 0 vibration on the surface. Mo (Ⅴ) sites on the surface may be the active sites for acid sites and methanol oxidation on the catalyst surface. No obvious change of Sn ~ (4+) valence was found in the catalyst.