摘要
应用氢化学吸附、透射电镜和选区电子衍射考察了Pt/Al_2O_3,PtSn/Al_2O_3催化剂经过n-C_4H_(10)反应积炭及氧烧炭循环后的晶粒、结构及表面吸附性质。发现多次循环后催化剂晶粒发生烧结,烧结程度为Pt/Al_2O_3>PtSr/Al_2O_3(分浸)>PtSn/Al_2O_3(络合)。选区电子衍射分析进一步揭示了双金属PtSn催化剂的活性组分物相的变化。络合法制备的PtSn催化剂经过循环处理后,双金属结构遭到破坏出现游离的Pt和Sn,催化剂氢吸附量呈现波动而降至很低。通过与无积炭直接氧化-还原循环的对比,表明积炭-烧炭循环中表面含炭物是引起烧结及双金属结构变化的主要因素。
Effect of coking-burning off cycle on the properties of two PtSn/Al2O3 catalysts prepared by impregnation with Sn prior to Pt [PtSn(s)] and by complex method [PtSn(c)], and of Pt/Al2O3 catalyst was studied by hydrogen chemisorption, electron microscope and selective area electron diffraction technique. TEM results show that the order of sintering is Pt>PtSn(s)>PtSn(c), i.e. the addition of Sn into Pt/Al2O3 increases its thermal stability, and the method of Sn addition exerts influence upon the sintering behavior. From the diffraction patterns, it is found that coking-burning off cycle results in the destruction of bimetallic clusters on PtSn(c) and the formation of metallic Pt and Sn, whereas the bimetallic components on PtSn(s) remains in most area. As segregation occurred, the Sn deposited on Pt surface and the amount of hydrogen chemisorbed by Pt decrease. For comparison, the oxidation-reduction' cycle on the catalysts was also performed. It is shown that the sintering and' segregation are mainly caused by carbonaceous on the surface of the catalysts, therefore, the stability of catalyst during regeneration depends upon the characteristics of metal-support-chemical environment interaction.
基金
中国科学院基金(R850851)
