State Key Joint Laboratory of Environment Simulation and Pollution Control, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
University of Chinese Academy of Sciences, Beijing 100049, China.
Environ Sci Technol. 2023 Jun 6;57(22):8426-8434. doi: 10.1021/acs.est.3c01444. Epub 2023 May 22.
The trade-off between activity and selectivity is a century-old puzzle in catalysis. In the selective catalytic reduction of NO with NH (NH-SCR), various typical oxide catalysts exhibit distinct characteristics of activity and selectivity: Mn-based catalysts show outstanding low-temperature activity and poor N selectivity, mainly caused by NO formation, while Fe- and V-based catalysts possess inverse characteristics. The underlying mechanism, however, has remained elusive. In this study, by combining experimental measurements and density functional theory calculations, we demonstrate that the distinct difference in the selectivity of oxide catalysts is determined by the gap in the energy barriers between N formation and NO formation from the consumption of the key intermediate NHNO. The gaps in the energy barriers follow the order of α-MnO < α-FeO < VO/TiO, in correspondence with the order of N selectivity of the catalysts. This work discloses the intrinsic link between the target reaction and side reactions in the selective catalytic reduction of NO, providing fundamental insights into the origin of selectivity.
活性和选择性之间的权衡是催化领域一个具有百年历史的难题。在 NH（NH-SCR）选择性催化还原 NO 过程中，各种典型的氧化物催化剂表现出明显的活性和选择性特征：Mn 基催化剂表现出优异的低温活性和较差的 N 选择性，主要是由于 NO 的形成，而 Fe 和 V 基催化剂则具有相反的特征。然而，其潜在的机制仍然难以捉摸。在这项研究中，通过结合实验测量和密度泛函理论计算，我们证明了氧化物催化剂选择性的显著差异取决于从关键中间体 NHNO 消耗中形成 N 和形成 NO 的能垒之间的差距。能垒的差距遵循 α-MnO < α-FeO < VO/TiO 的顺序，与催化剂的 N 选择性顺序相对应。这项工作揭示了目标反应与选择性催化还原 NO 过程中副反应之间的内在联系，为选择性的起源提供了基本的见解。
