Fig. 4: Transient oxygen switching experiments.
From: Elucidating the mechanism of heterogeneous Wacker oxidation over Pd-Cu/zeolite Y by transient XAS
a, b Normalized mass spectrometry (MS) signals of outlet gas components as a function of time during the transient oxygen switching experiments over Pd1Cu5-Y. Corresponding dynamic c, d copper and e, f palladium speciation determined from MCR-ALS of time-resolved XANES spectra. The fraction of Cu(II) species is the sum of hydrated and dehydrated copper species, the speciation of which are shown in Supplementary Figs. 13–16. The catalyst was equilibrated under Wacker conditions for 4 h before the first change in oxygen partial pressure (t < 0). After changing the partial pressure of oxygen (zero order to half order and back), the catalyst was subjected to the gas feed until the MS signals equilibrated. This kinetic regime switching experiment was carried out two more times and the results are provided in full detail in Supplementary Figs. 13–16. Gas feed composition (C2H4:H2O:O2) at high pO2 (1:7:10) and low pO2 (1:7:0.05) was balanced with helium to achieve a constant contact time in all experiments.
