Center for Excellence in Regional Atmospheric Environment and Key Laboratory of Urban Pollutant Conversion, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China.
University of Chinese Academy of Sciences, Beijing 100049, China.
Environ Sci Technol. 2020 Dec 1;54(23):15499-15506. doi: 10.1021/acs.est.0c06256. Epub 2020 Nov 17.
Cu-SSZ-13 and Cu-SSZ-39, with similar structures, are both highly active and hydrothermally stable in the selective catalytic reduction of NO with NH (NH-SCR), attracting great attention for applications on diesel vehicles. In this study, it was interestingly found that NO has distinct effects on the NO conversion over Cu-SSZ-13 and Cu-SSZ-39, with an inhibiting effect for Cu-SSZ-13 but a promoting effect for Cu-SSZ-39. The distinct NO effects were found to be associated with the differences in the reactivity of surface NHNO, a key intermediate for NH-SCR, on these two Cu-based small-pore zeolites. Cu-SSZ-13 has excellent standard SCR activity, but the reactivity of surface NHNO with NO is relatively low, which would induce the accumulation of NHNO on the surface and thus inhibit NO conversion. Surface Brønsted acid sites play key roles in the reduction of surface NHNO by NO, and Cu-SSZ-39 showed much higher surface acidity than Cu-SSZ-13. Compared with Cu-SSZ-13, the intrinsic standard SCR activity of Cu-SSZ-39 was lower but NHNO could be reduced by NO rapidly on Cu-SSZ-39, even faster than the reduction of NO by the adsorbed NH on Cu active sites; thus, NO conversion was promoted by NO on Cu-SSZ-39. This work provides an improved understanding of fast SCR on Cu-based small-pore zeolites.
Cu-SSZ-13 和 Cu-SSZ-39 结构相似，在 NH-SCR 中对 NO 的选择性催化还原具有很高的活性和水热稳定性，因此在柴油车应用方面引起了极大的关注。在这项研究中，有趣的是发现 NO 对 Cu-SSZ-13 和 Cu-SSZ-39 上的 NO 转化具有明显的影响，对 Cu-SSZ-13 有抑制作用，对 Cu-SSZ-39 有促进作用。这种明显的 NO 效应与两种 Cu 基小孔沸石上表面 NHNO 的反应性差异有关，NHNO 是 NH-SCR 的关键中间体。Cu-SSZ-13 具有优异的标准 SCR 活性，但与 NO 反应的表面 NHNO 活性相对较低，这会导致 NHNO 在表面上积累，从而抑制 NO 转化。表面 Brønsted 酸位在表面 NHNO 被 NO 还原中起关键作用，Cu-SSZ-39 比 Cu-SSZ-13 具有更高的表面酸度。与 Cu-SSZ-13 相比，Cu-SSZ-39 的固有标准 SCR 活性较低，但 NHNO 可以在 Cu-SSZ-39 上被 NO 迅速还原，甚至比吸附在 Cu 活性位上的 NH 还原 NO 还要快；因此，NO 促进了 Cu-SSZ-39 上的 NO 转化。这项工作提高了对基于 Cu 的小孔沸石上快速 SCR 的理解。
