原位漫反射红外光谱研究NO和NH_3在CuO/γ-Al_2O_3催化剂上的吸附行为

Adsorption of NO and NH_3 over CuO/γ-Al_2O_3 catalyst by DRIFTS

利用原位漫反射红外光谱法在线研究NH3和NO在CuO/γ-Al2O3催化剂表面吸附和氧化的反应过程。NH3不仅能被吸附在L酸位,也能被吸附在B酸位。NH3氧化脱氢形成NH2物种是反应的中间步骤。NO和NO2以多种形态吸附在催化剂表面。O2存在条件下有利于吸附的NO物种被氧化成高价的NO2。暂态实验中,吸附NH3饱和的催化剂载体通入NO和O2后,共价吸附的NH3首先消失,而NH+4没有参加反应。吸附NO饱和的催化剂载体通入NH3和O2后,吸附态NO特征峰基本没有变化。选择性催化还原反应发生在吸附态NH3和气态NO之间,吸附态的NO及其氧化生成的亚硝基和硝基物种不参与SCR反应。

Granular CuO/γ-Al2O3 catalysts were synthesized by the sol-gel method. The performance of CuO/γ-Al2O3 catalysts for selective catalytic reduction （SCR） was analyzed in a fixed bed adsorption system. The optimum temperature range for SCR reaction on CuO/γ-Al2O3 catalyst was 250- 450℃. Based on the previous study, CuO/γ-Al2O3 catalysts were investigated with in-situ diffuse reflectance infrared fourier transform spectroscopy （DRIFTS） for revealing the reaction mechanism. The DRIFTS indicated both coordinated NH3 and NH4^＋ were present on the catalysts. NO and NO2 could be adsorbed on the catalyst surface and produce a number of different transformation species. Formation of NO3 after O2 addition suggested the oxidation of adsorbed NO species to nitrates. When NO was introduced into the samples with pre-adsorbed NH3 ＋O2, the coordinated NH3 on the catalyst surface was consumed rapidly. But NH4^＋ was not consumed under the SCR reaction. It indicated that these coordinated NH3 species could react with NO effectively. When NH3 was introduced into the samples with pre-adsorbed NO＋O2 proceed. NO. The , the intensity of adsorbed NO species did It was found that the SCR reaction could not change; it inferred that SCR reaction would not take place between the adsorbed NHa and gaseous adsorbed NO and formed NO2^- and NO3^- species did not participate in the SCR reaction.