(689g) Identification of Multinuclear Copper Active Sites for NO Oxidation over Cu-SSZ-13

The identification and quantification of multinuclear Cu-oxo cations in Cu-zeolites is challenging. [1-3] We synthesized Cu-SSZ-13 zeolites with varying densities of monomeric Cu cations (Z₂Cu and ZCuOH, where Z represents an anionic site on the zeolite framework). [3] Parity between the number of Cu-oxo cations quantified using carbon monoxide temperature programmed reduction and the fraction of overlapping randomly distributed spheres of 0.5 nm radii from Monte Carlo simulations was observed, indicating that dehydrated Cu moieties have a diffusion sphere of ~0.5 nm. Further, NO oxidation rates collapse into a single parabola plotted against the ZCuOH density, evidencing that proximal ZCuOH sites are precursors to Cu-oxo cations. A turnover rate of 2.9·10^-4 s^-1 (300 ppm NO, 150 ppm NO₂, 10% O₂, balance inert, 1 atm total pressure, 300°C) is obtained when the rate is normalized to the number of Cu-oxo cations. [4] Although the precise structural and electronic nature of these Cu-oxo species are still unclear, understanding these site requirements will aid in devising strategies for more efficient zeolite catalysts.

References

1. Grundner, S., et al. "Single-site trinuclear copper oxygen clusters in mordenite for selective conversion of methane to methanol." Nature Communications 6.1 (2015): 1-9.
2. Ipek, B., et al. "Formation of [Cu₂O₂]²⁺ and [Cu₂O]²⁺ toward C–H bond activation in Cu-SSZ-13 and Cu-SSZ-39." ACS Catalysis 7.7 (2017): 4291-4303.
3. Paolucci, C., et al. "Dynamic multinuclear sites formed by mobilized copper ions in NO x selective catalytic reduction." Science 357.6354 (2017): 898-903.
4. Khurana, I., et al. "Identification and quantification of multinuclear Cu active sites derived from monomeric Cu moieties for dry NO oxidation over Cu-SSZ-13." Journal of Catalysis 413 (2022): 1111-1122.