Research Article

Dynamic multinuclear sites formed by mobilized copper ions in NOx selective catalytic reduction

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Science  17 Aug 2017:
DOI: 10.1126/science.aan5630

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Copper ions exchanged into zeolites are active for the selective catalytic reduction (SCR) of NOx with NH3, but the low-temperature rate dependence on 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 O2-mediated CuI → CuII redox step integral to SCR. Electrostatic tethering to framework Al 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.

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