摘要
通过混捏法制备了Pt-SO42-/ZrO2-Al2O3固体酸催化剂,考察了该催化剂在正构烷烃低温异构化反应中的催化稳定性.采用X射线衍射、差热分析、X射线光电子能谱、核磁共振、N2吸附-脱附和微量热等表征技术,对氧化铝的作用机理进行了研究.结果表明,氧化铝起到结构助催化剂作用,对四方相氧化锆具有稳定作用,并延迟了氧化锆的晶化,抑制了氧化锆的烧结,从而增大了催化剂的比表面积和孔容.XPS结果表明,Zr 3d峰向低结合能方向移动,Al 2p峰向高结合能方向移动,说明Al3+的电子向Zr4+偏移.微量热结果表明氧化铝的引入提高了催化剂的酸量和酸强度.27Al固体核磁共振结果表明,Pt-SO42-/ZrO2-Al2O3中的六配位铝的结构发生了变化.氧化铝的引入还可能有助于氧化锆晶格缺陷的形成,焙烧过程中Al3+迁移进入氧化锆晶格并同晶取代Zr4+形成氧缺陷位,这些氧缺陷位在S=O键诱导下显示强酸性.
Solid acid catalyst Pt-SO^42-/ZrO2-Al2O3 was prepared by a kneading method. Its stability for the isomerization of normal alkane at low temperature was evaluated in a flow microreactor-chromatogram system. The effect of alumina on physico-chemical properties of the catalyst was investigated by means of N2 adsorption-desorption, X-ray diffraction, differential thermal analysis, X-ray photoelectron spectroscopy, magic angle spinning nuclear magnetic resonance spectroscopy and microcalorimetry. As a structure co-catalyst, alumina can retard the crystallization of zirconia and restrain zirconia particles from sintering and agglomerating, so that the specific surface area and pore volume of the catalyst are increased. Alumina also inhibits the transformation of zirconia from a metastable tetragonal phase to a monoclinic phase. The XPS results indicate that an electron transfer from Al^3＋ to Zr^4＋ occurs. The ^27 Al MAS NMR results show that the structure of octahedral coordinated Al is changed. The number of acid sites is increased and the acid strength is enchanced in Pt-SO4^2-/ZrO2-Al2O3 compared with Pt-SO4^2-/ZrO2 according to the microcalorimetry results. A new acid site model is proposed, in which alumina also helps to form lattice defects in zirconia. When the catalyst is calcined, Al^3 ＋ ions move into the zirconia crystal lattice and replace Zr^4 ＋ ions so that the oxygen ion defects are generated. These oxygen ion defects show strong acidity under the induction of the S=O bond of SO4^2-.
出处
《催化学报》
SCIE
CAS
CSCD
北大核心
2005年第12期1067-1072,共6页
基金
国家重点基础研究发展计划(973计划)资助项目(G2000048002)
关键词
混捏法
铂
氧化锆
氧化铝
固体酸
正戊烷
异构化
酸位模型
kneading method, platinum, zirconia, alumina, solid acid, n-pentane, isomerization, acid site model
