化学学报 ›› 2004, Vol. 62 ›› Issue (14): 1311-1317. 上一篇    下一篇

Nb2O5/TiO2催化剂表面铌氧物种的分散状态和催化性能

何杰1,2, 范以宁1, 邱金恒1, 陈懿1   

  1. 1. 南京大学化学系, 介观材料实验室, 南京, 210093;
    2. 安徽理工大学, 化工系, 淮南, 232001
  • 投稿日期:2003-09-18 修回日期:2004-03-12 发布日期:2014-02-17
  • 通讯作者: 范以宁,E-mail:chem612@nju.edu.cn E-mail:chem612@nju.edu.cn
  • 基金资助:
    国家重点基础研究发展规划(No.G1999022400)和南京大学分析测试基金项目资助.

Dispersion State and Catalytic Properties of Niobia Species on the Surface of Nb2O5/TiO2 Catalysts

HE Jie1,2, FAN Yi-Ning1, QIU Jin-Heng1, CHEN Yi1   

  1. 1. Laboratory of Mesoscopic Materials Science, Department of Chemistry, Nanjing University, Nanjing 210093;
    2. Department of Chemical Engineering, Anhui University of Science and Technology, Huainan 232001
  • Received:2003-09-18 Revised:2004-03-12 Published:2014-02-17

用X射线粉末衍射(XRD)、拉曼光谱(LRS)、Hammett指示剂和微反测试等方法考察了负载型Nb2O5/TiO2催化剂表面铌氧(NbOx)物种的分散状态、表面酸性和催化异丁烯(IB)与异丁醛(IBA)缩合生成2,5-二甲基-2,4-己二烯(DMHD)反应的催化性能.实验测得Nb2O5在TiO2表面的分散容量为0.94mmol Nb/100m2TiO2,与"嵌入模型"理论计算值相近.当负载量低于分散容量的1/3时,Nb2O2主要以孤立的NbOx物种通过Nb-O-Ti链与载体表面相连,这种孤立的NbOx物种酸性很弱,催化活性很低.随负载量的增加,孤立的NbOx物种通过Nb-O-Nb键连接聚合,表面酸性增强,IB与IBA缩合生成DMHD的转化数(TON)增加.当Nb2O5负载量超过分散容量时,表面NbOx物种主要是通过Nb-O-Nb化学键相连形成多层的Nb2O5,虽然催化剂的强酸中心数量有所增加,但NbOx物种表面利用率下降,催化活性增加幅度趋缓.

关键词: Nb2O5, TiO2, 分散容量, 表面酸性, 烯醛缩合反应

The dispersion state, surface acidity and catalytic properties of anatase-supported niobia species have been studied by means of X-ray powder diffraction (XRD), laser Raman spectroscopy (LRS), Hammett indicator method and the condensation reaction of isobutene (IB) with isobutyraldehyde (IBA) to 2,5-dimethyl-2,4-hexadiene (DMHD).The almost identical values of the experimental dispersion capacity of Nb2O5 on anatase (0.94 mmol Nb/100 m2 TiO2) and the value derived theoretically by the incorporation model (0.98 mmol Nb/100 m2 TiO2) suggest that the highly dispersed niobium cations are bonded to the vacant sites on the preferentially exposed surface (001) of anatase.When the loading amount of Nb2O5 is below 1/3 of its dispersion capacity, the dispersed niobia species might mainly consist of isolated NbOx species bridging to the surface through Nb—O—Ti bonds.With the increase of Nb2O5 loading the isolated niobia species interact with their nearest neighbors through bridging Nb—O—Nb at the expenses of Nb—O—Ti bonds, resulting in the increase of the ratio of polymerized to isolated niobia species and the increase of surface acidic strength and catalytic activity for the condensation reaction.When the loading amount of Nb2O5 is higher than its dispersion capacity, the catalytic activity increases slightly with the increase of Nb2O5 loading due to the formation of bulk Nb2O5 in which Nb—O—Nb species are only partially exposed on the surface.

Key words: niobium pentaoxide, titanium oxide, dispersion capacity, surface acidity, olefin-aldehyde condensation reaction