K-MoO_3/γ-Al_2O_3催化剂表面物种状态、组成和性能

CHEMICAL STATES AND COMPOSITION OF THE SURFACE SPECIES OF K-MoO_3/γ-Al_2O_3 CATALYSTS

应用XPS、XRD、ESR 和TPR 技术分析了KCl 助剂含量变化对MoO_3/γ-Al_2O_3催化剂表面物种状态、组成及其硫化还原性能的影响.K/Mo 比小于0.8时,钾离子完全和钼作用,形成钾钼作用物种,催化剂硫化后发生K^+表面富集,Cl^-游离并流失;K/Mo 比0.8时,钾钼作用达到饱和;K/Mo 比大于0.8时,多余的K^+和Cl^-结合以体相KCl 形式存在.钾钼作用减弱了Mo(Ⅵ)和载体之间的作用,部分抑制了Mo(Ⅵ)的硫化还原.钾钼作用物种硫化后可能产生CO 合成醇的活性中心.

The chemical states and composition of the surface species of sulfided MoO_3/γ--Al_2O_3 catalysts with the promotion of variable KCI contents have been investigatedand correlated to the sulfidation and reduction properties of the catalysts by meansof XPS,XRD,ESR and TPR techniques.An interaction between the potassium ca-tions and the molybdenum component occurred and was stoichiometrically saturated ata KCI loading with the K/Mo atomic ratio of 0.8.At the K/Mo ratios below 0.8the potassium cations interacted with molybdenum component to form the interacting species and were enriched on the catalyst surface,while chloride anions were freeand lost during preparation.At the K/Mo ratios above 0.8 the surplus potassiumcations directly combined with the chloride anions to form bulk KCI crystallites.Dueto the existence of the potassium promoter,the interaction between the supportedMo(Ⅵ)and the γ-Al_2O_3 became weaker and the sulfidation and reduction for cata-lysts were partly retarded.The active sites or phases,which were responsible for thealcohol formation activity,could be produced by sulfiding the interacting speciescomposed of the potassium and molybdenum components.