State Key Laboratory of Chemical Resource Engineering, Beijing Key Laboratory of Energy Environmental Catalysis, Beijing University of Chemical Technology, Beijing 100029, P. R. China.
Beijing Synchrotron Radiation Facility (BSRF), Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, P. R. China.
Environ Sci Technol. 2021 Apr 20;55(8):5422-5434. doi: 10.1021/acs.est.0c08684. Epub 2021 Mar 15.
Conventional Cu-ZSM-5 and special Cu-ZSM-5 catalysts with diverse morphologies (nanoparticles, nanosheets, hollow spheres) were synthesized and comparatively investigated for their performances in the selective catalytic reduction (SCR) of NO to N with ammonia. Significant differences in SCR behavior were observed, and nanosheet-like Cu-ZSM-5 showed the best SCR performance with the lowest of 130 °C and nearly complete conversion in the temperature range of 200-400 °C. It was found that Cu-ZSM-5 nanosheets [mainly exposed (0 1 0) crystal plane] with abundant mesopores and framework Al species were favorable for the formation of high external surface areas and Al pairs, which influenced the local environment of Cu. This motivated the preferential formation of active copper species and the rapid switch between Cu and Cu species during NH-SCR, thus exhibiting the highest NO conversion. In situ diffused reflectance infrared Fourier transform spectroscopy (DRIFTS) results indicated that the Cu-ZSM-5 nanosheets were dominated by the Eley-Rideal (E-R) mechanism and the labile nitrite species (NHNO) were the crucial intermediates during the NH-SCR process, while the inert nitrates were more prone to generate on Cu-ZSM-5 nanoparticles and conventional one. The combined density functional theory (DFT) calculations revealed that the decomposition energy barrier of nitrosamide species (NHNO) on the (0 1 0) crystal plane of Cu-ZSM-5 was lower than those on (0 0 1) and (1 0 0) crystal planes. This study provides a strategy for the design of NH-SCR zeolite catalysts.
传统的 Cu-ZSM-5 和具有不同形态（纳米颗粒、纳米片、空心球）的特殊 Cu-ZSM-5 催化剂被合成并进行了比较研究，以评估它们在氨选择性催化还原（SCR）NO 为 N 的性能。观察到 SCR 行为存在显著差异，纳米片状 Cu-ZSM-5 表现出最佳的 SCR 性能，最低反应温度为 130°C，在 200-400°C 的温度范围内几乎完全转化。研究发现，Cu-ZSM-5 纳米片（主要暴露（010）晶面）具有丰富的介孔和骨架 Al 物种，有利于形成高的外部比表面积和 Al 对，从而影响 Cu 的局部环境。这促使活性铜物种的优先形成和 NH-SCR 过程中 Cu 和 Cu 物种之间的快速转换，从而表现出最高的 NO 转化率。原位漫反射红外傅里叶变换光谱（DRIFTS）结果表明，Cu-ZSM-5 纳米片主要遵循 Eley-Rideal（E-R）机制，并且亚硝酸盐物种（NHNO）是 NH-SCR 过程中的关键中间体，而惰性硝酸盐更容易在 Cu-ZSM-5 纳米颗粒和常规催化剂上生成。综合密度泛函理论（DFT）计算表明，硝酰胺物种（NHNO）在 Cu-ZSM-5（010）晶面上的分解能垒低于在（001）和（100）晶面上的分解能垒。该研究为设计 NH-SCR 沸石催化剂提供了一种策略。
