Using Transient FTIR Spectroscopy to Probe Active Sites and Reaction Intermediates for Selective Catalytic Reduction of NO on Cu/SSZ-13 Catalysts

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A Cu/SSZ-13 catalyst containing predominately Z 2 Cu sites is prepared. Using FTIR spectroscopy, two nonsteady-state measurements, (1) continuous NO titration of an NH 3 saturated catalyst and (2) intermittent NO on/off cycles 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 NH 3 inhibition effect is found, where Cu active sites containing NH 3 ligands are less active than Cu sites depleted of NH 3 ligands. In the NO perturbation experiments, it is demonstrated that NO+NH 3 interactions lead to formation of Brønsted acid sites, which further interact with NH 3 to form NH 4 + . Perturbation measurements, using ND 3 to replace NH 3 in order to distinguish ammonia and nitrate vibrations, further show that NH 4 NO 3 and other surface nitrates are not involved in the SCR process under typical low-temperature quasi-steady-state conditions.