Near ambient pressure XPS investigation of the interaction of ethanol with Co/CeO2(1 1 1)

• Catalytic activity of ceria and of ceria-supported cobalt particles studied by NAP-XPS.
• Reduction of ceria upon ethanol exposure.
• Cobalt particles are partly oxidized upon deposition on ceria.
• Reduction of the cobalt particles and the ceria support upon ethanol exposure.
• Coke formation on cobalt particles during reaction at 600 K.

Near ambient pressure X-ray photoelectron spectroscopy was applied to study the interaction of ethanol (CH3CH2OH) with a well-ordered CeO2(1 1 1) film on Cu(1 1 1) and with a Co/CeO2(1 1 1)/Cu(1 1 1) model catalyst. The oxidation state of the surface and the chemical nature of reaction intermediates were analyzed. At 300 K, the oxidation state of ceria decreased gradually with increasing ethanol pressure. At a constant pressure of 0.1 mbar, the reduction of Ce4+ to Ce3+ increased significantly between 320 and 600 K due to a higher mobility of oxygen or Ce3+ centers at elevated temperatures. The main intermediate, ethoxide, was formed by dissociative adsorption of ethanol at room temperature. No coke formation was observed up to 600 K on CeO2. Upon deposition of metallic cobalt, partial reduction of ceria was observed, leading to the formation of Co2+ sites but still leaving metallic Co in the metal particles. During the reaction of ethanol with the Co/CeO2(1 1 1) model catalyst, the amount of Co2+ decreased drastically with increasing temperature, and at 600 K, the majority of Co was metallic. This process was accompanied by the severe reduction of ceria and the formation of significant carbon deposits.

The adsorption of ethanol on ceria and cobalt particles on ceria were investigated at pressures of up to 1 mbar with near ambient pressure XPS. The adsorption of ethanol on the clean ceria lead to a gradual reduction with increasing pressure already at 300 K, with the reduction being more pronounced at higher temperatures. The main intermediate, ethoxide, was formed by dissociative adsorption of ethanol at room temperature. Upon deposition of metallic cobalt on ceria, partial reduction of ceria and the oxidation of the cobalt particles to Co 2+ was observed. The reaction of ethanol with the Co/CeO2(111) model catalyst up to 600 K led to severe reduction of cobalt and ceria, as well as coke formation.Figure optionsDownload high-quality image (126 K)Download as PowerPoint slide