Ag/Al_2O_3催化乙醇和甲醚选择性还原NO_x反应机理的原位红外光谱研究

Mechanistic Study of Selective Catalytic Reduction of NO_x with C_2H_5OH and CH_3OCH_3 over Ag/Al_2O_3 by in Situ DRIFTS

尽管C2H5OH和CH3OCH3是同分异构体,但在以Ag/Al2O3为催化剂选择性催化还原NOx时,还原剂C2H5OH比CH3OCH3具有更高的活性.原位漫反射红外光谱研究表明,C2H5OH和CH3OCH3在还原NOx反应过程中分别遵循不同的反应机理:在Ag/Al2O3催化C2H5OH还原剂选择性还原NOx的反应过程中,烯醇式物种(RCH=CH-O-)和NO3-物种是主要的反应中间体,二者相互反应性能很强,可以生成反应关键中间体异氰酸酯(-NCO)表面吸附物种,因此NOx的去除率很高;而在Ag/Al2O3催化CH3OCH3还原剂选择性还原NOx的反应过程中,甲酸盐(HCOO-)物种和NO3-物种是主要的反应中间体,二者之间反应生成-NCO的活性较弱,因而NOx的去除率较低.

Although C2H5OH and CH3OCH3 are isomeric compounds, C2H5OH is extremely efficient for NOx, reduction while it is not the case for CH3OCH3. In situ diffuse reflectance infrared Fourier transform spectroscopy （DRIFTS） was used to study the reaction mechanism. The enolic species derived from partial oxidation of C2H5OH over Ag/Al2O3 plays a crucial role in the -NCO species formation during the selective catalytic reduction （SCR） of NOx. by C2H5OH. The high reactivity of the enolic species results in high surface concentration of -NCO species and high efficiency of NOx reduction when using C2H5OH as a reductant. In the case of CH3OCH3, the formate species as a main intermediate has lower activity for the formation of -NCO species, which results in the relatively low efficiency during the SCR of NOx