摘要
证明了高温还原的Pt-Al_2O_3催化剂形成难还原的Pt离子(即可溶性Pt)的关键因素是Al_2O_3表面要有强Lewis酸中心,而Cl离子的存在和适宜的焙烧温度则是生成可溶性Pt的必要条件,根据这些事实提出了生成可溶性Pt的模型。
The relative amount of soluble Pt (i.e. unreduced ionic Pt, NP1) over Pt-Al2O3, which was prepared by the impregnation of A12O3 with H2PtCl6, increased with the increase of strong Lewis acid center. When the Lewis acid center of A12O3 was neutralized by Na2O,K2O before loading H2PtCl6, only a little soluble Pt was detected. By the way,the relation of NPI with the amount of soluble Al3+ of A12O3 was similar to the relation between NPI and the number of strong Lewis acid center.The catalyst prepared by impregnating A12O3 with H2PtCl6 or Pt(NH3)4-C12 contained a quite large amount of soluble Pt, while the soluble Pt of the catalyst impregnated with Pt(NH3)4(OH)2was essentially absent. Moreover, the removal of Cl in the catalyst prepared by impregnation with H2PtCl6 decreased greatly the soluble Pt, and the amount of soluble Pt was resumed to original value by the readdition of Cl-.It was worthy to note that the catalyst calcined at an appropriate temperature (e.g. 500℃)was also the essential prerequisite for the formation of soluble Pt, the amount of soluble Pt of the uncalcined catalyst was very low.
