组合型Pt/TiO_2催化剂用于低温催化甲苯完全氧化

Low-Temperature Total Oxidation of Toluene over Assembled Pt/TiO_2 Catalyst

将均匀分布的纳米Pt粒子直接吸附到TiO2载体上,即制得了组合型Pt/TiO2催化剂(Pt/TiO2-AS).与浸渍法制备的Pt/TiO2催化剂(Pt/TiO2-WI)比较,Pt/TiO2-AS催化剂在催化甲苯完全氧化反应中表现出了很好的催化性能,甲苯转化率为100%时的反应温度低至150°C,而且即使在较高甲苯浓度和较高气体空速下,该催化剂也能保持较好的催化性能.通过X射线衍射(XRD)、N2吸附-脱附(BET)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)、氢气程序升温还原(H2-TPR)及傅里叶变换红外(FTIR)光谱等对两种Pt/TiO2催化剂的结构和表面性能进行了表征.结果表明组合型Pt/TiO2-AS催化剂粒径小(2.5 nm),活性组分主要以Pt0形式存在且分布在载体表面,而且载体表面Ti―O键活化使催化剂具有较强的催化氧化能力.另外,活性中心的价态变化(Pt0→Ptδ+)是导致Pt/TiO2-AS催化剂失活的主要原因.

A highly active assembled Pt/TiO2 catalyst (Pt/TiO2-AS) was synthesized using a simple direct-adsorption method, in which uniformly dispersed Pt nanoparticles were directly loaded on a TiO2 support. Compared with Pt/TiO2 produced by wet impregnation (Pt/TiO2-WI), the Pt/TiO2-AS catalyst exhibited higher activity in the total oxidation of toluene, with a toluene conversion to CO2 and H2O of 100% at 150 °C. The high activity remained even at high toluene concentrations and gas hourly space velocities. The properties of the synthesized catalysts were characterized using X- ray diffraction (XRD), N2 adsorption- desorption (Brunauer-Emmett-Tel er (BET) method), transmission electron microscopy (TEM), X- ray photoelectron spectroscopy (XPS), temperature-programmed reduction of H2 (H2-TPR), and Fourier-transform infrared (FTIR) spectroscopy. The results showed that the Pt/TiO2-AS crystal ites were smal er than those of Pt/TiO2-WI, with fine dispersion, greater Pt0 exposure on the support surface, and more active Ti-O bands, giving more oxygen vacancies and reactive oxygen species. The valence states of the active centers changed significantly (Pt0→Ptδ +) during stability tests; this is the main reason for the deactivation of the Pt/TiO2-AS catalyst.