Pt/Al_2O_3催化剂用于NO氧化的活化效应研究

Degreening Effect During NO Oxidation over Pt/Al_2O_3 Catalyst

柴油机氧化催化剂(DOC)能将尾气中部分NO氧化成NO_2,一定浓度的NO_2有利于柴油机颗粒捕集器(DPF)的连续再生和提高选择性催化还原催化剂(SCR)对NO_x的转化效率。针对DOC的新鲜态Pt/Al_2O_3 催化剂经过1次程序升温NO催化氧化活性明显提升的现象(活化效应),采用原位红外漫反射实验(in situ DRIFTS)、氢气程序升温还原、X射线光电子能谱(XPS)和高分辨透射电子显微镜(HR-TEM)分析Pt/Al_2O_3催化剂相关过程的物理化学状态。分析结果表明,新鲜态Pt/Al_2O_3催化剂在300℃以下时载体上积累了大量的硝酸盐和亚硝酸盐物种,导致新鲜态催化剂活性不高;进一步的分析表明经一次程序升温后催化剂中与载体结合强的PtO_x物种的分解是引起活化效应的主要原因;经过3次程序升温反应,催化剂中Pt粒子的大小没有发生明显改变。

Part of NO is oxidized to NO2 when the emission gas goes through diesel oxidation catalysts（DOC）. Proper NO2/NOx concentration increases the low-temperature soot oxidation rate of diesel particulate filter（DPF） and the NOx conversion efficiency of selective catalytic reduction catalyst（SCR）. In order to study the degreening effect of DOC, in-situ diffuse reflectance infrared Fourier transform spectroscopy（In-situ DRFTS）, H2 temperature-programmed reduction（H2-TPR）, X-ray photoelectron spectroscopy（XPS）and High-revolution transmission electron microscope（HR-TEM） were used to characterize the Pt/Al2O3 catalyst. Results show that a large amount of nitrate and nitrite species are accumulated in the fresh Pt/Al2O3 catalysts below 300℃, which causes the low activity of fresh catalysts. The decomposition of PtOx species that interacts strongly with the substrate is the main cause of degreening effect after one temperature-programmed reaction. The particle size of Pt has no significant change after 3-cycle temperature-programmed reaction.