Comparative study on hydrogenation of propanal on Ni(111) and Cu(111) from density functional theory

Highlights: • Hydrogenation of propanal is kinetically much faster on Ni(111) than Cu(111). • Hydroxyl route is prefered over alkoxy route on Ni(111). • Alkoxy route is prefered over hydroxyl route on Cu(111). • Activation barrier for hydrogenation of carbonyl is lowered by H-tunneling effect. • η²(C,O)-adsorption mode is beneficial for hydrogenation/dehydrogenation of aldehyde. - Abstract: Using propanal as a probe molecule, we have comparatively investigated hydrogenation of carbonyl (C=O) in short carbon-chain aldehyde on Ni(111) and Cu(111) by means of periodic density functional theory. Our focus is in particular on the differentiation of reaction route in sequential hydrogenation on Ni(111) and Cu(111) following Langmuir–Hinshelwood mechanism. Strong binding with alkoxy intermediates has great impact on altering reaction pathways on the two surfaces, where hydroxyl route via 1-hydroxyl propyl intermediate is dominant on Ni(111), but alkoxy route via propoxyl intermediate is more likely on Cu(111) due to a higher activiation barrier of initial hydrogenation in hydroxyl route. In comparison, hydrogenation of carbonyl on Ni(111) is kinetically much faster than that on Cu(111) as a result of much lower activation barrier in rate-determining step (i.e., 13.2 vs 26.8 kcal/mol) of most favorable reaction pathways. Furthermore, the discrepancy in calculated and experimental barriers can be well explained by using the concept of H-tunneling effect on bond forming with H atoms during sequential hydrogenation. The different features of electronic structure exhibited by the two metal surfaces provide insight into their catalytic behaviors.