Theoretical investigation of the reactivity of flat Ni (111) and stepped Ni (211) surfaces for acetic acid hydrogenation to ethanol

Reactivity of two types of Ni surfaces-flat (111) and stepped (211) surfaces for acetic acid hydrogenation to ethanol was investigated using density functional theory method. The most stable configurations of the reactants, intermediates and products were obtained by investigating all the possible adsorption sites. Results showed that the adsorption of all the studied molecules on the Ni (211) surface are stronger than that on the Ni (111) surface, except for H atom (similar adsorption strength of H atom on the both surfaces was found). In addition, most of the molecules on the Ni (211) surface preferred to adsorb at the step edge, indicating that different coordination numbers of Ni atoms could result in different adsorption strength. Moreover, the elementary reactions with energy barriers related to ethanol and ethyl acetate formations were studied. The most favorable pathways for ethanol formation on the Ni (111) and (211) surfaces are CH3COOH -> CH3CO -> CH3CHO -> CH3CHOH -> CH3CH2OH and CH3COOH -> CH3CO -> CH3COH -> CH3CHOH -> CH3CH2OH, respectively. The direct decomposition of acetic acid molecule to form acetyl species was the rate-determining step on the both surfaces. Slight difference for the rate-determining step barriers was observed (1.04 eV vs. 1.13 eV). However, the elementary step of ethyl acetate formation by CH3CO and CH3CH2O became much more difficult on the Ni (211) surface than that on the Ni (111) surface (1.06 eV vs. 0.67 eV). These results suggests that the Ni (211) surface is more likely to inhibit ethyl acetate formation compared with the Ni (111) surface. Meanwhile, the results of the rate constants and the effective barriers in-dicates that the Ni (211) surface presents a higher probability for higher ethanol selectivity. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

The reactivity of Ni surfaces for acetic acid hydrogenation to ethanol was studied using density functional theory method. Results showed that Ni (211) surface has stronger adsorption and may be more favorable for ethanol selectivity.