Rich/lean cycling is used to study the total oxidation of methane over a Pd/Al₂O₃ catalyst at different oxidation states. Time-resolved energy-dispersive X-ray absorption fine structure is used in a modulation excitation approach to monitor the chemical state of the palladium nanoparticles during the cycling, and the resulting spectra are demodulated using phase sensitive detection. Cycling is performed using oxygen pulses with a concentration of 0.15, 0.25, and 1.5% over a constant flow of 0.1% methane. For the two lowest oxygen concentrations the methane conversion is generally low but increases at the switches between the rich and the lean periods, while for the highest oxygen concentration the conversion is highest during the lean periods. The oxidation state of Pd changes rapidly but to a limited extent for the two lowest oxygen concentrations, whereas for the high oxygen concentration the oxidation appears to proceed via a two-step process, where the first step is rapid and the second step is slower. EXAFS fitting of the demodulated spectra is used to quantify the Pd oxidation state, the first rapid oxidation step is assigned to surface oxidation, while the second step is assigned to bulk oxidation of Pd. A low methane conversion is observed when the Pd nanoparticles are covered with chemisorbed oxygen or surface oxide, the methane conversion is higher when the Pd nanoparticles are bulk oxidized.

富/稀循环用于研究Pd / Al ₂ O ₃上甲烷的总氧化催化剂在不同的氧化态。时间分辨的能量色散X射线吸收精细结构在调制激发方法中用于监视循环过程中钯纳米粒子的化学状态，并使用相敏检测对所得光谱进行解调。使用浓度为0.15、0.25和1.5％的氧气脉冲在0.1％甲烷的恒定流量上进行循环。对于两个最低的氧气浓度，甲烷转化率通常较低，但在富油期和稀燃期之间的转换时会增加，而对于最高的氧气浓度，在贫油期转化率最高。Pd的氧化态迅速变化，但对于两个最低的氧浓度而言，变化程度有限。而对于高氧气浓度，氧化似乎是通过两步过程进行的，其中第一步是快速的，而第二步是较慢的。解调后的光谱的EXAFS拟合用于量化Pd的氧化态，第一个快速氧化步骤分配给表面氧化，而第二个步骤分配给Pd的整体氧化。当Pd纳米颗粒被化学吸附的氧气或表面氧化物覆盖时，甲烷转化率较低；当Pd纳米颗粒被大量氧化时，甲烷转化率较高。