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Abstract
The O removal through water formation is an important process in the Fischer–Tropsch synthesis. In this study, both steps in water formation (O+H→OH, OH+H→H2O) are studied on the stepped Co(0001) at high coverages using density functional theory. We find the following. (i) In both O–O and O–OH co-adsorption systems, two transition states (TSs) were located for the O hydrogenation: in one TS, both O and H are on the same terrace, and in the other they are at the interface between the step edge and the terrace below. (ii) In both the O–O and O–OH co-adsorption systems, the O hydrogenation at the interface is easier (E a = 0.32 eV in the O–O system, E a = 1.10 eV in the O–OH system) than that on the same terrace (E a = 1.49 eV in the O–O system, E a = 1.80 eV in the O–OH system). (iii) In both the O–O and O–OH co-adsorption systems, only one TS for the OH hydrogenation was located, in which both OH and H are on the same terrace. (iv) Compared to the OH hydrogenation in the O–OH system (E a = 1.46 eV), the reaction in the OH–OH system (E a = 0.64 eV) is much easier. The barrier differences and the water effect on the Fischer–Tropsch synthesis are discussed. A possible route with low barriers for water formation is proposed.
Notes
Dedicated to Professor Ruth Lynden-Bell on her retirement.