Fig. 3: Redox dynamics of palladium species during simulated lean/rich cycles.
From: Anchoring PdOx clusters on defective alumina for improved catalytic methane oxidation
a White line region of operando X-ray absorption near-edge spectroscopy (XANES) recorded at 1 s time resolution obtained upon switching between CH4 and O2. b Plots of Pd2+ and Pd0 relative contents over Pd/Al2O3 (top) and Pd/Al2O3-x (bottom) catalysts as a function of time, in the alternating CH4/O2 pulses. (Reaction temperature: 400 °C, and GHSV = 7,643 h−1). c Plot of online CO2 mass spectrometry (MS) signal as a function of time in a representative modulation excitation (ME) cycle. The variation in the content of Pd0 species over Pd/Al2O3 (d) and Pd/Al2O3-x (e) across the first to ninth reduction/oxidation cycles of the ME experiment, as a function of the relative CH4/O2 composition. The inserted bar chart illustrates the variation in the integrated area of the loops formed by the increase (during the reduction process) and decrease (during the oxidation process) of Pd0 species in each oxidation/reduction cycle, as a function of the cycle number. Error bars indicate the 95% confidence interval.
