A comparative study of ethanol reactivity over Ni, Co and NiCo-ZnO model catalysts

• The ethanol decomposition pathway on ZnO supported NiCo was studied by TPD.
• Dehydrogenation of OH group takes place as a first step, generating adsorbed ethoxy species.
• High Ni content favors methane desorption and Boudouard reaction.
• High cobalt content tends to favor ethoxy group dehydrogenation.
• The selectivity to methane decomposition is determined by the Ni and Co content.

The interaction of ethanol with a model catalyst consisting of Ni, Co and Ni-Co nanoparticles supported on Zn terminated polar ZnO(0 0 0 1) single crystals, was investigated by temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). The TPD spectra recorded upon ethanol exposure on Ni-Co layers with different Ni:Co composition (Ni atomic fraction = 0, 0.37, 0.54, 0.64, 1) show several desorption products as a result of ethanol dehydrogenation and decomposition reactions. XPS results revealed that the Ni-Co thin layer agglomerated upon annealing, while evidence of oxygen spillover from the ZnO support to the NiCo overlayer was found. Chemisorbed ethanol readily reacts with the model catalysts and desorbs as C2H4O (243 K), CH4 (243 K), H2 (258 K), CO (312 K and 440 K) and CO2 (at 363 K). Ethanol decomposition and desorption of methane is more favorable on Ni rich NiCo layers. On the other hand, dehydrogenation of ethanol and production of acetaldehyde is more pronounced on cobalt. In addition, mobile oxygen from the ZnO support participates to the oxidation of carbonaceous species at higher temperatures, preventing carbon deposition. This work provides new insights into the intrinsic reactivity of ethanol over NiCo-ZnO, which can be of a great importance in understanding the selectivity and stability of these catalysts in the ethanol steam reforming reaction.

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