NO_2对Cu/SAPO-34分子筛催化剂上NH_3选择性催化还原NO性能的影响  

Effect of NO_2 on the Selective Catalytic Reduction of NO with NH_3 over Cu/SAPO-(34) Molecular Sieve Catalyst

作　　者：郝腾[1] 王军[1] 于铁[1] 王建强[1] 沈美庆[1,2] 

机构地区：[1]天津大学化工学院,绿色合成与转化教育部重点实验室,天津300072 [2]天津大学内燃机国家重点实验室,天津300072

出　　处：《物理化学学报》2014年第8期1567-1574,共8页Acta Physico-Chimica Sinica

基　　金：supported by the National High-Tech Research and Development Program of China(863)(2011AA03A405)~~

摘　　要：主要考察了NO2对Cu/SAPO-34分子筛催化剂在整个温度范围内(100-500°C)NH3选择性催化还原(SCR)NO性能的影响.研究所使用样品为新鲜Cu/SAPO-34催化剂在750°C下水热处理4 h的稳定期样品.通过X射线衍射(XRD)和扫描电子显微镜(SEM)对样品的结构以及形貌进行表征,采用SCR活性评价、动力学实验以及原位漫反射傅里叶变换红外光谱(in situ-DRIFTS)表征催化剂的性能以及催化剂表面物种的变化.活性评价实验结果表明,NO2会抑制催化剂的低温(100-280°C)活性,但其存在会提高催化剂的高温(280°C以上)活性.与此同时,随着反应物中NO/NO2的摩尔比例减少,由于NH4NO3物种的分解,副产物(N2O)的浓度增大.动力学结果表明,Cu/SAPO-34催化剂上快速SCR反应的表观活化能(Ea=64.02 kJ?mol-1)比标准SCR反应的表观活化能(Ea=48.00 kJ?mol-1)更大.In situ-DRIFTS实验结果表明NO比NO2更容易在催化剂表面形成硝酸盐,并且NO2更容易与吸附在Br?nsted酸性位上的NH3物种反应生成NH4NO3.低温下,催化剂表面的NH4NO3物种会覆盖SCR反应的活性位,造成活性降低,但在高温时,形成的NH4NO3物种一部分会被NO还原为N2,而另一部分会直接热分解为N2O,造成催化剂的选择性降低.This study investigated the effects of NO2 on the selective catalytic reduction （SCR） of NO by NH3 over Cu/SAPO-34 catalyst at temperatures ranging from 100 to 500 ℃. The Cu/SAPO-34 sample was hydrothermally treated at 750℃ for 4 h to obtain a degreened sample and X-ray diffraction （XRD） and scanning electron microscopy （SEM） were used to characterize the structure of the catalyst. SCR activity test, kinetic analysis, and in situ diffuse reflectance infrared Fourier transform spectroscopy （in situ-DRIFTS） were all applied to evaluate the changes in catalytic activity in the presence of various NO/NO2 ratios. The SCR results for different NO/NO2 molar ratios demonstrated that NO2 inhibited the NOx removal efficiency over the Cu/SAPO- 34 catalyst at low temperatures （100-280 ℃）, but enhanced the efficiency at high temperatures （above 280 ℃）. The amount of N20 was observed to increase with decreasing NO/NO2 ratios, owing to the decomposition of NH4NO3. The kinetic results showed that the fast SCR reaction exhibited a higher apparent activation energy （Ea=64.02 kJ·mol-1） than that of the standard SCR reaction （Ea=48.00 kJ·mol-1） over Cu/SAPO-34 catalyst. The results of in situ-DRIFTS showed that NO2 did not efficiently generate nitrate species on Cu^2＋ sites compared with NO, and that some nitrate species combined with NH^4＋ on Brensted acid sites to generate NH4NO3. The inhibitory effect of NO2 at low temperatures is evidently caused by deposited NH4NO3 covering the active sites of Cu/SAPO-34 catalyst, while these NH4NO3 species can be reduced by NO or thermally decomposed as the temperature increases.

关 键 词：NH3选择性催化还原 NOx(NO和NO2) CU SAPO-34 漫反射傅里叶变换红外光谱 硝酸铵 

分 类 号：O643.32[理学—物理化学]