In situ DRIFTS and temperature-programmed technology study on NH3-SCR of NOx over Cu-SSZ-13 and Cu-SAPO-34 catalysts
In situ DRIFTS and temperature-programmed technology study on NH3-SCR of NOx over Cu-SSZ-13 and Cu-SAPO-34 catalysts
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DOI：
10.1016/j.apcatb.2014.03.048
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发表时间：
2014-09-01
影响因子：
22.1
通讯作者：
Li, Junhua
中科院分区：
文献类型：
--
作者：
Ma, Lei;Cheng, Yisun;Li, Junhua
采用原位漫反射红外傅里叶变换光谱(原位DRIFTS)、程序升温脱附(TPD)和程序升温表面反应(TPSR)等方法考察了CuSSZ-13和CuSAPO-34沸石催化剂的吸附和反应性能，并在750℃的模拟进气中进行了水热处理。根据表征结果，提出了NH3-SCR活性差异的内在机理和原因。原位DIFTS和TPD结果表明，氨气同时吸附在两种催化剂的Lewis和Bronsted酸性中心上，Bronsted酸性中心上的氨气可能是NH3-SCR反应中的活性物质。对于不同的NOx吸附过程，NO的总脱附水平依次为：NO<；NO+O-2<；NO2=NO2+O-2。结果表明，在低温和高温范围内，CuSSZ-13和CuSAPO-34催化剂上的反应路径完全不同。在低温范围内，表面氨与硝酸盐反应生成的硝酸铵是关键中间体，并被NO气体进一步还原为N-2和H2O。在高温范围内，气相NO2在NH3-SCR反应中的作用逐渐增强。活性测试表明，在整个反应温度范围内，Cu-SAPO-34催化剂的Deno(X)性能相对高于Cu-SSZ-13催化剂，呈现双峰形状，浸润点约为390℃。Cu-SAPO-34可能保留了许多表面硝酸盐物种，而不会产生比Cu-SSZ-13多得多的NO2气体；该物种在390℃阻碍了SCR反应。(C)2014 Elsevier B.V.
In situ diffuse reflectance infrared Fourier transform spectroscopy (In situ DRIFTS), temperature-programmed desorption (TPD), and temperature-programmed surface reactions (TPSR) were employed to investigate the adsorption and reactive properties of Cu-SSZ-13 and Cu-SAPO-34 zeolite catalysts; these fully formulated washcoat cordierite monoliths were hydrothermally treated at 750 degrees C in the simulated feed gases. The intrinsic mechanism and reasons for the differences in NH3-SCR activity were proposed based on the characterization results. The in situ DRIFTS and TPD results showed that ammonia could adsorb on both the Lewis and Bronsted acidic sites on these two catalysts; the ammonia on the Bronsted acidic sites might be active in the NH3-SCR reaction. For the different NOx adsorption processes, the total NO desorption levels followed the following sequence: NO < NO + O-2 < NO2 = NO2 + O-2. The results confirm that the reaction pathways are totally different in the low and high temperature ranges on the Cu-SSZ-13 and Cu-SAPO-34 catalysts. In the low temperature range, the ammonium nitrates from the reaction between surface ammonia and nitrates are the key intermediates and are further reduced to form N-2 and H2O by the NO gas. In the high temperature range, the gas-phase NO2 gradually become more important in the NH3-SCR reaction. The activity tests indicated that the Cu-SAPO-34 catalyst had a relatively higher DeNO(x) performance than the Cu-SSZ-13 catalyst across the entire reaction temperature range, showing a double peak shapes with a dip point at approximately 390 degrees C. Cu-SAPO-34 might retain many surface nitrate species and did not produce much more NO2 gas than Cu-SSZ-13; this species hindered the SCR reaction at 390 degrees C. (C) 2014 Elsevier B.V. All rights reserved.