Role of hydrogen absorption in supported Pd nanocatalysts during CO-PROX: insights from operando X-ray Absorption Spectroscopy
Résumé
The nature of the active phase (metallic vs. oxidic, metal phase vs. concentrated hydride/ diluted solid solution with hydrogen) in heterogeneous catalysis by supported metals is still a matter of high debate.1 Here, we have monitored for the first time oxide-supported Pd nanocatalysts (average particle size 4.5 nm) during both CO oxidation (in H2-free atmosphere) and preferential oxidation of CO in H2 excess (PROX) by operando X-ray absorption spectroscopy (Rock beamline at Soleil). Under our conditions, the CO conversion in the absence of H2 is around 30% at 150 °C and reaches 100% at 200 °C, whereas in the presence of H2 the conversion reaches a maximum of 15% (at 250 °C), in agreement with our previous works using a conventional flow-fixed bed reactor.2 The active phase for CO oxidation below 200 °C is metallic Pd, whereas it is a solid solution of Pd with hydrogen during PROX below 300 °C. This presentation will clarify the role of hydrogen in supported Pd catalysts during the PROX reaction.3
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3. C. Zlotea, Y. Oumellal, K. Provost, F. Morfin, L.Piccolo, Applied Catalysis B: Environmental 237, 1059-1065 (2018)