To examine whether auto-reduction (steps 1 -3, Scheme 1) possibly contributes to the formation of ZCuOCuZ, we investigated the influence of different reductive pretreatments of ZCuOH sites. Auto-reduction treatments of ZCuOH species in He at 723 K do not fully reduce all Cu(II) complexes present to Cu(I) (Figure ). Rather, treatments in He yield a combination of ZCu + , ZCuxOyHz, and Z2Cu species that do not auto-reduce. The Raman active ZCuOCuZ species seem unlikely to form via the dehydration of ZCu(OH)2CuZ (step 2, Scheme 1), because no Raman features appear at elevated temperatures in He (Figure ). We also used Raman spectrokinetics to measure rates of ZCuOCuZ formation over Cu-CHA-I samples treated in carbon monoxide (5 kPa CO, 96 kPa He, 523 K), which fully reduces multinuclear CuxOy sites to ZCu + . Following these CO pretreatments, we observe ZCuOCuZ formation rates that depend on O2 pressure, temperature, and D2O/H2O (Section S8) similarly as Cu-CHA-I instead auto-reduced in He. These comparisons demonstrate that step 1 and step 2 are not kinetically relevant for the formation of the ZCuOCuZ complex after a He auto-reduction treatment. Finally, we must note that this sequence of reactions (steps 1 -3, Scheme 1) does not involve gaseous O2; therefore, these steps do not explain the dependence of ZCuOCuZ formation rates on the pressure of O2 (Figs and). Consequently, the subsequent and slower formation of the Raman active ZCuOCuZ complexes must reflect steps 6a or 6b if O-O bond rupture limits rates.