In Situ-DRIFTS Study of Selective Catalytic Reduction of NOx by NH3 over Cu-Exchanged SAPO-34
In Situ-DRIFTS Study of Selective Catalytic Reduction of NOx by NH3 over Cu-Exchanged SAPO-34
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DOI：
10.1021/cs300843k
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发表时间：
2013-05-01
期刊：
影响因子：
12.9
通讯作者：
Epling, William S.
中科院分区：
文献类型：
--
作者：
Wang, Di;Zhang, Li;Epling, William S.
采用原位漫反射红外傅立叶变换光谱（DRIFTS）技术，结合质谱法测定了铜交换SAPO-34催化剂在低温下选择性催化还原（SCR）反应的内在机理。评价了NH3与表面中间体、NH3与表面中间体、NOx和NOx与表面NH3的反应性。在对NOx的吸附方面，表面硝酸盐和亚硝酸盐是低温下主要的NOx吸附种类。当NO暴露在预吸附NH3的样品中时，由于硝酸盐和亚硝酸盐的表面覆盖率低，表面NH3不发生反应。然而，在饲料中加入O-2显著提高了反应性，促进了表面硝酸盐和亚硝酸盐浓度的增加。DRIFTS结果还表明，低温SCR反应涉及NH4NO3中间体的形成及其随后被NO还原。NH4NO3在Cu-SAPO-34样品的Lewis酸位上形成。Bronsted酸位点作为NH3储存器，通过迁移到Lewis酸位点为SCR反应提供额外的NH3。在NH3-温度程序解吸（TPD）研究中证实了NH3在不同酸位点之间的迁移。进料中NO的存在使表面NH4NO3在低至100℃的温度下还原生成N-2。由于NH4NO3通常被认为是一种抑制剂，因此NO和NH4NO3之间反应的起始温度远低于其他SCR沸石催化剂的起始温度；因此，这可能是导致Cu-SAPO-34低温SCR活性的关键因素。
The intrinsic Mechanism of the selective catalytic reduction (SCR), reaction over a Cu-exchanged SAPO-34 catalyst at low temperature was studied by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), coupled With mass spectrometry to measure inlet and Outlet gas concentrations. The evolution of the surface : intermediates, as well as the reactivity of NH3 with,surface,NOx species and NOx with surface NH3 species, was evaluated. In terms of NOx adsorption, surface nitrates and nitrites are the main NOx adsorption species at low temperature. When NO was exposed to the sample with NH3 preadsorbed, surface NH3 was not reactive because of the low surface coverage of nitrates and nitrites. However, the reactivity is significantly enhanced by the inclusion of O-2 in the feed, which promotes an increase in the concentration of surface nitrates and nitrites. DRIFTS results also reveal that the low temperature SCR reaction involves the formation of an NH4NO3 intermediate and its subsequent reduction by NO. The NH4NO3 was formed on Lewis, acid sites on the Cu-SAPO-34 sample. The Bronsted acid sites act as an NH3 reservoir that supplies additional NH3 via migration to the Lewis acid sites for the SCR reaction. The migration of NH3 between different acid sites was confirmed in an NH3-temperature-programmed desorption (TPD) study. The presence of NO in the feed reduces surface NH4NO3 to produce N-2 at temperatures as low as 100 degrees C. Since NH4NO3 is typically considered an inhibitor the onset temperature of the reaction between NO and NH4NO3 is much lower than that reported for other SCR zeolite catalysts; therefore, it is likely the key factor that results in the low temperature SCR activity of Cu-SAPO-34. .