Engineering oxygen vacancy-rich CeOx overcoating onto Ni/Al2O3 by atomic layer deposition for bi-reforming of methane

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Atomic layer deposition (ALD) was applied to develop CeOx-overcoated Ni/Al2O3 catalyst for bi-reforming of methane (BRM), as the combination of dry reforming of methane (DRM) and steam reforming of methane (SRM). Non-stoichiometric CeOx thin films were successfully deposited on Ni/Al2O3 particles by ALD, which constructed a beneficial Ni-CeOx interface and modified the catalyst property. Ascribed to the unique ALD growth mode, a high amount of Ce(III) and oxygen vacancies existed in the ALD-deposited CeOx overcoating. A reduction process before the BRM reaction contributed to the further reduction of Ce(IV) to Ce(III), resulting in more oxygen vacancies. The oxygen vacancies at the Ni-CeOx interface enabled a high rate of CO2 activation and enabled the balance between the activation of CO2 and H2O for BRM. Due to its oxygen vacancies as activation sites for CO2 and H2O, CeOx ALD overcoating significantly improved the activity of Ni/Al2O3 catalyst and achieved a better control in the H2/CO ratio with a suitable ratio of H2O/CO2/CH4 feed. CeOx overcoatings enhanced the reducibility of Ni(II) sites and assisted in preventing Ni from oxidation during the BRM reaction. Less carbon deposition was achieved by the Ni/Al2O3 catalyst with CeOx overcoating as ascribed to its better reactant activation capacity.