Abstract:

The interaction between Pt and the carrier affects the catalytic activity of the intrinsic Pt nanoparticles. Herein, Pt/CeO₂ catalyst was successfully prepared via a facile Pt colloidal particle deposition method, and its physicochemical properties and catalytic performance in CO oxidation and toluene combustion were investigated. XRD, TEM, XPS and H₂-TPR were used to identify the states of Pt particles on the support surface, as well as their effect on the performance of the catalysts. Formation of metallic Pt⁰ which provided the active sites for CO oxidation and toluene combustion is one of the factors controlling catalyst activity. Pt/CeO₂ catalyst prepared by colloidal particle deposition was found to be more advantageous than conventional impregnation and impregnation-reduction in producing very finely dispersed metallic Pt⁰ that did not noticeably agglomerate even after thermal treatment at 400℃ for longer duration. The CO oxidation and toluene combustion activity additionally demonstrate that the sample shows a remarkably better performance as compared to its impregnated counterparts. By contrast, all of Pt atoms were anchored with the surface oxygen of CeO₂ by forming Pt-O-Ce bond during the oxidative treatment in impregnation method, resulting in the absence of metallic Pt⁰. This change is evidence of the appearance of Pt²⁺ species, which is supported by the H₂-TPR and XPS data, and could be the main reason behind the deactivation of the Pt/CeO₂ catalyst. Compared with impregnation method, the dispersion of metallic Pt⁰ rised while less Pt-O-Ce bonds existed on the support surface, and a higher Pt⁰/Pt²⁺ ratio could be maintained even under the high thermal treatment in impregnation reduction method. The catalytic activity test of CO oxidation and toluene combustion show that the sample exhibits the better catalytic performance due to the increase of surface metallic Pt⁰,but it is unavoidable for the sample to show a decline in catalytic activity compared with its colloidal particle depositional counterpart. Hence, it is concluded that the state and the dispersion of Pt nanoparticles on the support surface depended on the prepared method, and they are the decisive factors to promote the catalytic activity of Pt/CeO₂ upon the oxidative treatment, especially the abundant surface metallic Pt⁰. Based on characterization results, the colloidal particle deposition method is proposed to realize the direct load of metallic Pt⁰ and gives the homogeneous dispersion of Pt nanoparticles, possessing a superiority in improving the catalytic performance.

Key words: Pt/CeO₂ catalysts, Pt nanoparticles, CO oxidation, impregnation, colloid deposition

摘要：

Pt与载体间的相互作用会影响到本征Pt纳米粒子的催化活性，不同Pt前体制备Pt/CeO₂催化剂会使其表现出完全不同的催化性能。分别采用金属胶体粒子原位沉积法、浸渍法以及浸渍还原的方式制备了Pt/CeO₂催化剂，通过X 射线衍射、程序升温还原、X射线光电子能谱以及高分辨透射电镜对催化剂进行表征，在CO氧化以及甲苯燃烧反应中评价催化剂活性。结果表明，胶体粒子原位沉积法制备Pt/CeO₂催化剂，能够将优先合成好的Pt纳米粒子直接以金属态Pt⁰的形式负载到载体表面，且保证其高度均匀分散，丰富的表面Pt⁰很好地充当了CO、甲苯反应时的活化位点，催化剂表现出优异的性能；浸渍还原法中，Pt纳米粒子之间会发生团聚现象，同时部分Pt又以Pt²⁺的形式与CeO₂之间形成了Pt-O-Ce相互作用，载体表面暴露Pt⁰含量的下降是催化剂表现出较弱活性的主要原因；浸渍法中，以Pt离子对Pt进行负载，Pt完全以Pt²⁺的形式参与到Pt-O-Ce键成键中，表面Pt⁰缺失，催化剂表现出明显的失活现象。Pt/CeO₂催化剂中，起主要活性作用的是金属态Pt⁰，胶体粒子原位沉积法能够实现Pt⁰的直接负载，对于提高Pt基催化剂中Pt的利用率，降低Pt资源消耗都具有重要意义。

关键词: Pt/CeO₂催化剂, Pt纳米粒子, CO氧化, 浸渍法, 胶体沉积