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

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