Effect of the balance between Co(II) and Co(0) oxidation states on the catalytic activity of cobalt catalysts for Ethanol Steam Reforming

• Cobalt catalyst supported on alumina for ethanol steam reforming reactions.
• In situ and operando Quick-XAS combined with Raman spectroscopy and mass spectrometry.
• The calcination temperature influences the interaction of cobalt with support.
• The equilibrium between Co2+/Co0 ratio equilibrated ethanol conversion and carbon oxidation.

Changes of the oxidation state of cobalt species during activation under H2 gas and ethanol steam reforming reaction on Co/Al2O3 were investigated using time-resolved operando Quick-XAS analysis. Prior to activation and reaction, the catalysts were calcined at two different temperatures: 450 and 600 °C, the cobalt species of the as-calcined catalysts are slightly different depending on the temperature of calcination. At the end of activation the same amount of metallic cobalt (∼63%) was detected for both catalysts calcined at different temperatures. The cobalt species interacted more strongly with the support in the catalyst calcined at 600 °C, what resulted in the formation of more cobalt aluminate species and lower amount of Co2+. A relationship between the catalytic performance of catalyst and the molar ratio of Co2+/Co0 was established: deactivation of catalysts mainly occurred by carbon deposition, however the control of Co2+/Co0 ratio helped to equilibrate the steps of ethanol activation and carbon oxidation, resulting in stable catalysts. The catalysts calcined at 450 °C were more stable and exhibited higher hydrogen selectivity.

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