Time-resolved operando X-ray absorption study of CuO-CeO₂/Al₂O₃ catalyst during total oxidation of propane

The local structure of the copper phase of a CuO-CeO₂/Al₂O₃ catalyst and its activity for the total oxidation of propane have been studied under working conditions, using time-resolved X-ray absorption spectroscopy (XAS) in transmission mode at the Cu K edge coupled with on-line mass spectrometry (MS). In the temperature range of 573-723 K, the copper phase of the catalyst remains oxidized (i.e. Cu²⁺) during total oxidation reaction conditions (1%C₃H₈-5%O₂/He), while three species are present (i.e. Cu²⁺, Cu¹⁺ and Cu⁰) during reduction (2%C₃H₈/He) and re-oxidation (10%O₂/He) treatments where a two-step mechanism is found. Catalyst reduction is fully reversible, as the Cu²⁺ nature of the catalyst is recovered after a reduction-oxidation cycle. Re-oxidation of the catalyst is two orders of magnitude faster than its reduction and has an apparent activation energy of 24 kJ/mol. On the other hand, catalyst reduction requires an apparent activation energy of 70 kJ/mol, which is equal to the apparent activation energy determined under total oxidation reaction conditions. These results give support to a Mars-van-Krevelen reaction scheme with the copper phase of the catalyst being close to a fully oxidized state.