Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, IN 46556, USA.
Charles D. Davidson School of Chemical Engineering, Purdue University, 480 Stadium Mall Drive, West Lafayette, IN 47907, USA.
Science. 2017 Sep 1;357(6354):898-903. doi: 10.1126/science.aan5630. Epub 2017 Aug 17.
Copper ions exchanged into zeolites are active for the selective catalytic reduction (SCR) of nitrogen oxides (NO ) with ammonia (NH), but the low-temperature rate dependence on copper (Cu) volumetric density is inconsistent with reaction at single sites. We combine steady-state and transient kinetic measurements, x-ray absorption spectroscopy, and first-principles calculations to demonstrate that under reaction conditions, mobilized Cu ions can travel through zeolite windows and form transient ion pairs that participate in an oxygen (O)-mediated Cu→Cu redox step integral to SCR. Electrostatic tethering to framework aluminum centers limits the volume that each ion can explore and thus its capacity to form an ion pair. The dynamic, reversible formation of multinuclear sites from mobilized single atoms represents a distinct phenomenon that falls outside the conventional boundaries of a heterogeneous or homogeneous catalyst.
铜离子交换进入沸石后，对氨（NH）选择性催化还原（SCR）氮氧化物（NO）具有活性，但低温下对铜（Cu）体积密度的速率依赖性与单分子反应不一致。我们结合稳态和瞬态动力学测量、X 射线吸收光谱和第一性原理计算，证明在反应条件下，可移动的 Cu 离子可以穿过沸石窗口，并形成瞬态离子对，参与氧（O）介导的 Cu→Cu 氧化还原步骤，这是 SCR 的关键步骤。静电束缚在骨架铝中心限制了每个离子可以探索的体积，从而限制了形成离子对的能力。从可移动的单原子动态可逆形成多核位点代表了一种明显的现象，超出了异相或均相催化剂的传统界限。
