Detection of key transient Cu intermediates in SSZ-13 during NH₃-SCR deNO_x by modulation excitation IR spectroscopy

Abstract

Protagonists in the standard SCR reaction have been caught in the act by modulation excitation IR & XAFS spectroscopy.

Mechanistic insights into the oxidation of copper(i) species during NH3-SCR over Cu-CHA zeolites: a DFT study

“…(5). Greenaway et al25 have detected several key transient Cu intermediates including the Cu-NO3 in the NH3-SCR over Cu-CHA using the modulation excitation IR spectroscopy.…”

Experimental and Theoretical Studies of Sonically Prepared Cu–Y, Cu–USY and Cu–ZSM-5 Catalysts for SCR deNOx

“…According to the literature [62,65], Lewis acidity relates mainly to exchanged or introduced (here, Cu nanoparticles) transition metal oxides. However, extra-framework Al 3+ centers may also act as Lewis acid centers [62,66,67]. Additionally, ammonia sorption exhibited an additional band at ca.…”

Investigating the role of Cu-oxo species in Cu-nitrate formation over Cu-CHA catalysts

“… 27 Whereas Zhang et al used modulated FTIR measurements to conclude that no significant amount of nitrate is formed during the NH 3 -SCR cycle, 49 Greenaway et al showed some nitrate formation using a similar approach. 40 …”

“…19,20 Some aspects are still under debate in the oxidation half cycle regarding the role of NO in mediating the activation of O 2 , [22][23][24]29 and which is the structure of the formed intermediates relevant for the catalytic cycle. 18,19,27,28,[37][38][39][40][41] Cu-(NQO)-NH 2 (copper nitrosamine) species, postulated for both the reduction and oxidation half cycles, 18,39 have been recently detected using transient modulation excitation spectroscopic experiments. 40 NO oxidation on Cu II ions has been proposed to form unstable gas-phase HONO in equilibrium with surface nitrites, and where HONO is supposed to react with NH 3 to release N 2 .…”