关键词: 金属-载体强相互作用, 青铜矿, 晶相转变, 几何包覆, CO氧化

The strong metal-support interaction (SMSI) has long been studied in heterogonous catalysis on account of its importance in stabilizing active metals and tuning catalytic performance. So far, although there are many reports about SMSI in Pt-TiO₂ system, they are mainly focusing on support structure sensitivity (crystal plane effect) and the size of supported noble metals (size effect), it is still unclear whether the TiO₂ crystalline phase influences the creation of SMSI or not. In this study, we choose brookite TiO₂ (TiO₂(B)) as support to prepare Pt-TiO₂(B) catalyst by means of traditional impregnation method. Then the as-prepared Pt_imp/TiO₂(B) was treated at different temperature under different atmosphere, specifically, 250 ℃ heat treatment under H₂ (the sample is labeled as Pt_imp/TiO₂(B)-H250), 500 ℃ heat treatment under H₂ (the sample is labeled as Pt_imp/TiO₂(B)-H500), and 400 ℃ heat treatment under O₂ followed by H₂ treatment at 500 ℃ (the sample is labeled as Pt_imp/TiO₂(B)-H500+O400). The experimental results show that the 500 ℃ heat treatment under H₂ atmosphere induces the crystalline phase transformation of TiO₂(B) into anatase, and more importantly, this transformation leads to the TiO_2-x migration as a result of the encapsulation of Pt particles by TiO_2-x. After further heat treatment at 400 ℃ under O₂ atmosphere, the TiO_2-x shell coated on the Pt nanoparticle surfaces was removed, which displays a classical SMSI behavior. According to the high resolution transmission electron microscope (HRTEM) and CO diffuse reflectance infrared Fourier transform spectroscopy (CO-DRIFTS) results, we proposed that the crystalline phase transformation plays a great role in the creation of SMSI. In addition, we selected CO oxidation as a model reaction to compare the catalytic activity of Pt_imp/TiO₂(B) catalysts. The results demonstrate that the activity of the catalysts is simultaneously affected by the TiO_2-x coating on Pt nanoparticles and the oxygen vacancy concentration within the support. More specifically, compared with TiO₂(B), anatase TiO₂ has abundant oxygen vacancies, which is of great importance to activate O₂. In the case of Pt_imp/TiO₂(B)-H500+O400 catalyst, the active sites of Pt nanoparticles are exposed due to the removal of TiO_2-x coating, and the anatase TiO₂ has a certain amount of oxygen vacancies. Therefore, Pt_imp/TiO₂(B)-H500+O400 catalyst exhibits the best activity among all compared Pt/TiO₂(B) catalyst. Obviously, this work greatly enriches the SMSI for Pt/TiO₂ system, and provides an important reference value for the creation of SMSI, if any, when other crystalline phase transformation (or phase transformation) involved supports are suitably chosen.

Key words: strong metal-support interaction, TiO₂(B), phase change, physical coating, CO oxidation