用TDPAC技术表征Mo/γ—Al_2O_3加氢脱硫催化剂

(99)~Mo(β-)~(99)Tc时间微分扰动角关联法应用于加氢脱硫Mo/γ-Al_2O_3催化剂的表面性质研究,通过测定催化剂上钼原子的核电四极矩相互作用来表征催化剂表面的不同钼物种。并与噻吩加氢脱硫活性相关联。氧化态催化剂主要存在八面体配位钼物种MoO]和加氢脱硫活性中心的前身态Mo(Ⅵ)_前。氢还原态催化剂主要含有八面体配位的四价钼物种Mo~(4+)O]和加氢脱硫活性中心的前身态MO(Ⅳ)_前。Mo(Ⅵ)_前和Mo(Ⅳ)_前在催化剂表面上单层分散,与载体之间有较强的相互作用,具有抗氨水溶解能力,其含量主要受催化剂钼含量,助剂钴原子和催化剂焙烧温度等因素影响。MoO]在催化剂表面上可多层存在,与载体表面之间的相互作用较弱。

Characterization of Different Surface Mo Species of Mo/γ-Al_2O_3 Hydrodesulfurization Catalysts by Time Differential Perturbed Angular Correlation

The time differential determination of the perturbed Angular correlation of γ-rays emitted from radioactive (99)~Mo(β-)~(99)Tc allows one to characterize different surface Mo species in Mo/γ-Al_2O_3 HDS catalysts by their nuclear quadrupole interaction, and theywere related to HDS activities. The Mo/~-A1203 catalysts in ixidic stste(or in reduced stste) contained mostly octahedrally coordinated Mo~(6+)species-MoO](or Mo~(4+)species Mo~(4+)O]) and Mo species Mo(Ⅵ)_p(or Mo(Ⅳ)_p)as the precussors of active sites for HDS. Mo(Ⅵ)_pand Mo(Ⅳ)_p species in monolayer form existed preferentially on the catalyst surface and were the precussors of the active sulfided state for HDS. The Mo content of the catalysts, calcination temperature and Co pmmotor aflected significantly the amount of Mo (Ⅵ)_p species. MoO] species partly in mulfilayer form could exist on the catalyst surface. There were stronger interaction of Mo(Ⅵ)_p species with the support than that of MoO].