高热稳定性纳米Au/TiO2催化剂的制备与表征

 采用三嵌段共聚物聚乙醚-聚丙醚-聚乙醚EO20PO70EO20 (P123)为有机模板剂合成了介孔TiO2载体,用沉积-沉淀法制得Au/TiO2催化剂. 运用N2 吸附-脱附、 X射线衍射、 X射线光电子能谱和高分辨电镜技术对催化剂的结构与形貌进行了表征. 采用P123模板剂合成的TiO2具有较均匀的介孔结构,孔径集中在6.1 nm附近,负载金后,其介孔结构保持良好,但孔径下降至5.4 nm. 400 ℃焙烧后,介孔TiO2负载的Au催化剂中Au主要以金属态存在. 负载在三种TiO2载体(介孔TiO2、溶胶-凝胶法合成的TiO2和工业TiO2)上的Au晶粒大小和分散度差异较大,其中介孔TiO2载体更有利于金的分散,以该载体制备的催化剂400 ℃焙烧后金的晶粒尺寸在1～5 nm范围内,催化剂显示了很好的CO氧化活性和抗热稳定性,即使在420 ℃焙烧,其室温下CO的转化率也在90%以上. 而溶胶-凝胶法制备的TiO2和工业TiO2负载的纳米金催化剂中,金晶粒尺寸约为10 nm,催化剂的CO氧化活性和抗热稳定性较差.

Preparation and Characterization of Nanostructured Au/TiO2 Catalyst with High Thermal Stability

Mesoporous TiO₂ was synthesized using triblock copolymer EO₂₀PO₇₀EO₂₀ (P123) as the organic template, and the Au/TiO₂ catalyst was prepared by the deposition-precipitation method. For comparison, industrial TiO₂ and a TiO₂ sample synthesized by the sol-gel method were also used as supports to prepare the Au/TiO₂ catalysts. N₂ adsorption-desorption, X-ray diffraction, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy were employed to characterize the structure and the morphology of the catalysts. The results show that the TiO₂ support synthesized using P123 as the organic template possesses uniform mesoporous structure with a narrow pore size distribution centered at 6.1 nm. After Au is supported on TiO₂, the mesoporous structure of TiO₂ is well maintained and the pore size is decreased to 5.4 nm. The gold in the mesoporous TiO₂-supported catalyst calcined at 400°C exists as Au⁰. The dispersion and the crystal size of Au on the three types of TiO₂ show considerable difference. On the TiO₂ prepared using P123, the crystal size of Au is 1-5 nm after calcination at 400°C, while on the other two supports, the crystal size of Au reaches 10 nm. The former Au/TiO₂ catalyst exhibits very high activity and thermal stability for the ambient CO oxidation reaction even after calcination at 420°C, and the CO conversion over this catalyst is higher than 90%. The other two Au catalysts, which were prepared using industrial TiO₂ and the TiO₂ support synthesized by the sol-gel method, exhibit poor thermal stability and catalytic activity.