掺杂La^(3+)对纳米Au/TiO_2催化剂结构和性能的影响  

Effect of La^(3+) Doping on the Structures and Performance of Nano-structured Au/TiO_2 Catalysts

作　　者：侯凯军[1] 孟明[1] 邹志强[1] 吕倩[1] 

机构地区：[1]天津大学化工学院催化科学与工程系,天津300072

出　　处：《无机化学学报》2007年第9期1538-1544,共7页Chinese Journal of Inorganic Chemistry

基　　金：国家高技术研究发展计划(863计划)(No.2006AA06Z348);国家自然科学基金(No.20676097)资助项目。

摘　　要：采用三嵌段共聚物聚乙醚-聚丙醚-聚乙醚EO_(20)PO_(70)EO_(20)(P123)为有机模板剂分别合成了纯的和掺杂少量La^(3+)的介孔TiO_2载体,用沉积-沉淀法制得负载金催化剂。运用N_2吸附-脱附(BET)、X射线衍射(XRD)、X射线光电子能谱(XPS)、高分辨电镜技术(HR-TEM)和X射线能量分散谱(EDX)对催化剂的结构与形貌进行了表征。BET结果表明,采用P123为模板剂合成的纯TiO2具有较大的比表面积(103m2·g-1)和均一的介孔结构(￣4.1nm),掺杂La^(3+)后,其比表面积进一步提高到122m^2·g^(-1),同时孔径也有所增大(￣4.9nm)。450℃焙烧后,Au/TiO_2催化剂的介孔结构已部分被破坏,而Au/La-TiO_2催化剂仍保持较均匀的介孔结构;Au/TiO_2催化剂表面的Au主要以金属态存在,而Au/La-TiO_2催化剂表面除Au0外,还有少量Au_2O_3物种。HR-TEM结果表明,400℃焙烧后,Au/TiO2催化剂上金晶粒尺寸在6￣8nm范围内,而Au/La-TiO_2催化剂上金晶粒尺寸在5nm左右;450℃焙烧后,Au/TiO2中金晶粒尺寸显著提高至20nm以上,而Au/La-TiO_2中金晶粒尺寸仅在9nm左右。活性测试结果表明,400℃及以下温度焙烧的Au/TiO_2和Au/La-TiO_2催化剂均显示出很好的CO氧化活性,室温下就能将CO完全氧化。但是,经450℃焙烧后,Au/TiO_2催化剂上CO完全氧化温度高达86℃,而在Au/La-TiO_2催化剂上仅为53℃。少量La^(3+)的掺杂有效抑制了金晶粒的烧结,使金催化剂具有较高的活性和热稳定性。The mesoporous TiO2 and La-TiO2 were synthesized by using P123 as an organic template, and the supported gold catalysts were prepared by using deposit-precipitation method. The N2 adsorption-desorption, XRD, XPS, HR-TEM and Energy Dispersive X-ray （EDX） analysis techniques were employed to characterize the structures of the catalysts. The results of N2 adsorption-desorption show that the synthesized TiO2 possesses high surface area （103 m^2 ·g^-1） and uniform mesoporous structure with the pore size mainly centered at -4.1 nm. With the doping of La^3＋, the surface area and the pore size of La^3＋ doped mesoporous TiO2 increase to 122 m^2·g^-1 and -4.9 nm, respectively. After calcination at 450 ℃, the mesoporous structure of Au/TiO2 has collapsed partly, while that of Au/La-TiO2 is well maintained. The gold in Au/TiO2 calcined at 450 ℃ exists as Au^0, but in La^3＋ doped catalyst there is a small portion of Au2O3 in addition to Au^0. The results of HR-TEM show that after calcination at 400 ℃, the crystallite sizes of Au in Au/TiO2 and Au/La-TiO2 are 6-8 nm and -5 nm, respectively. After calcination at 450 ℃, the Au crystallites in Au/TiO2 increase to above 20 nm, while in Au/La-TiO2 they still keep very small size of -9 nm. For ambient CO oxidation, all the catalysts calcined at 400 ℃ or below exhibit excellent activity. After calcination at 450℃, the temperature for the full conversion of CO over Au/TiO2 reaches 86 ℃, while the temperature is only 53 ℃ over Au/La-TiO2. The doping of a small amount of La^3＋ effectively inhibits the sintering of Au crystallites, and therefore, makes the catalyst possess good activity and high thermal stability.

关 键 词：纳米金催化剂 一氧化碳氧化 介孔二氧化钛 P123模板剂 掺杂 LA^3+ 

分 类 号：O614.331[理学—无机化学] O614.123[理学—化学]