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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.
The effects of NO2 on the catalytic performance of NH3 selective catalytic reduction (SCR) for Cu / SAPO-34 molecular sieve catalyst over the entire temperature range (100-500 ° C) were investigated. The samples used were fresh Cu / SAPO-34 catalyst The samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The samples were characterized by SCR activity, kinetic experiments and in-situ diffuse reflectance In situ-DRIFTS was used to characterize the performance of the catalyst and the change of species on the catalyst surface. The results of the activity evaluation showed that NO2 inhibited the low temperature (100-280 ° C) activity of the catalyst, High temperature (above 280 ° C) .At the same time, the concentration of by-products (N2O) increased due to the decomposition of NH4NO3 species as the molar ratio of NO / NO2 in the reactants decreased.The kinetic results showed that the Cu / SAPO The apparent activation energy (Ea = 64.02 kJ? Mol-1) of the rapid SCR reaction on -34 catalyst is larger than that of the standard SCR reaction (Ea = 48.00 kJ mol-1) .In situ-DRIFTS experimental results It is shown that nitric oxide is more easily formed on the surface of catalyst than NO2, and NO2 is more tolerant NH3NO3 easily reacts with NH3 species adsorbed on Brönsted acidic sites.At the low temperature, the NH4NO3 species on the surface of the catalyst will cover the active site of the SCR reaction, resulting in a decrease of activity, but at high temperature, part of the formed NH4NO3 species will be replaced by NO Reduced to N2, while the other part of the direct thermal decomposition of N2O, resulting in reduced selectivity of the catalyst.