PNNL

Abstract

A Cu/SSZ-13 catalyst containing predominately Z2Cu sites is prepared. Using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), two non-steady state measurements, (1) continuous NO titration of an NH3 saturated catalyst and (2) intermittent NO on/off during quasi-steady state (i.e., NO perturbation), are conducted to shed light on active sites, reaction intermediates, and possible reaction mechanisms. During continuous NO titration, a strong NH3 inhibition effect is found, where Cu active sites containing NH3 ligands are less active than Cu sites depleted of NH3 ligands. In the NO perturbation experiments, it is demonstrated that NO+NH3 interactions lead to formation of Brønsted acid sites, which further interact with NH3 to form NH4+. Such a finding is fully consistent with a redox SCR mechanism proposed recently (Angew. Chem. Int. Ed. 2014, 53, 11828–11833). Perturbation measurements, using ND3 to replace NH3 in order to distinguish ammonia and nitrate vibrations, further show that NH4NO3 and other surface nitrates are not involved in the SCR process under typical low temperature quasi-steady state conditions. This work was financially supported by the national key research and development program of China (2017YFC0211302 and 2017YFC0211003), the Sino Japanese cooperation project (2016YFE0126600) and the China Postdoctoral Science Foundation (2017M620800). FG and CHFP gratefully acknowledge financial support for their participation from the US Department of Energy (DOE), Energy Efficiency and Renewable Energy, Vehicle Technologies Office. A portion of this work was performed in the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US DOE by Battelle.