We have investigated various Cu/Zeolite catalysts for the selective catalytic reduction (SCR) of NOx by NH3 via operando X-ray absorption spectroscopy (XAS) and complementary DFT and first principles thermodynamics calculations on the Cu/SSZ-13.  Under steady-state standard SCR (NO2/NOx=0) conditions, 15, 45 or 65% of Cu on SSZ-13, SAPO-34 and ZSM-5, respectively, was found to be in the Cu(I) oxidation state.  For fast (NO2/NOx=0.5) or slow (NO2/NOx=1) SCR, however, no Cu(I) could be detected.  The modeled Cu/SSZ-13 confirmed the presence of both Cu(II) and Cu(I) as the thermodynamically most abundant species under SCR.  Furthermore, the calculations capture the change in equilibrium Cu oxidation state from Cu(II) to Cu(I) as the conditions become more reducing.  In combination, these results indicate that the standard SCR reaction proceeds through a Cu redox cycle where the relative abundance of reduced Cu(I) sites is controlled by the ratio of steady-state rates of Cu oxidation and reduction.

Experimental and computational probing of the nature of exchange sites on Cu/CHA and Cu/MFI for the selective catalytic reduction of NO<sub>x</sub> by NH<sub>3</sub>

243rd National Meeting (2012)

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Experimental and computational probing of the nature of exchange sites on Cu/CHA and Cu/MFI for the selective catalytic reduction of NOx by NH3

Experimental and computational probing of the nature of exchange sites on Cu/CHA and Cu/MFI for the selective catalytic reduction of NO_x by NH₃