摘要
前一篇论文我们考察了TiO_2添加剂对MoO_3/γ-Al_2O_3表面分散状态的影响.本文将着重介绍XPS法对MoO_3-CoO-TiO_2/γ-Al_2O_3催化剂硫化态的表征,考察在工作状态下 (硫化态)TiO_2对MoO_3-CoO/γ-Al_2O_3催化剂的还原状态,硫化程度的影响及Ti-Mo间的相互作用,揭示了含Ti HDS催化剂具有不预硫化及在处理低硫含量的物料时个需要补硫而仍有高活性等特点的原因.
The surface chemical properties of sulfided Mo-Co-Ti / γ-Al2O3 hydrodesulfurization (HDS) catalysts were characterized by X-ray photoelectron spectroscopy (XPS) .In order to reveal the role of TiO2 in Mo-Co-Ti/γ-Al2O3 catalyst,the corresponding catalyst without TiO2was also studied for comparison.
The catalysts were prepared by incipient wetness impregnation method and the loading amount of MoO3, CoO and TiO2 is 12% (wt) , 3% (wt) , 0-9% (wt) respectively.
The results show that the intensity ratio of XPS signal I Mo Ⅳ 3d /IMoV 3d equals to 0.8-0.9 for TiO2\containing catalysts but only equals to 0. 5 when TiO2 is absent. This means that TiO2 promotes the reduction of MoⅥand increases the degree of reduction of MoⅥ, which is
reduced to MoⅣ .Moreover, the intensity ratio of Is2p/IMo3d for TiO2 containing catalysts equals to 0.21, but for catalyst with no TiO2 only equals to 0.11. This indicates that TiO2 also promotes the sulfidation of the catalysts.
It is noteworthy that all of the catalysts containing TiO2 in the range of 5-9% have the same value of the intensity ratio of Is2p/ IMo 3d.It is speculated that the sulfidation of Mo in Mo-Co-Ti /γ-A12O3 catalyst is homogeneous and there is a fixed atomic ratio of Mo / S under our sulfiding conditions.
A good correlation was found between the ease toward reduction and the facileness to-wards sulfidation of these catalysts, i.e. the catalyst which is readily reduced is also sulfided easily .This result supports the following suggestion of the sulfidation mechanism of Mo:
The results given above are attributed to the following reasons: (l)TiO2 improves the dispersity of MoO3 on support; (2)TiO2 weakens the interaction of Al2O3 and MoO3;
(3)TiO2 promotes the flow of electrons in the reduction and sulfiding reactions according to the model on page 157
出处
《分子催化》
EI
CAS
CSCD
1989年第2期155-158,共4页
Journal of Molecular Catalysis(China)
