Selective Hydrogenation of 1,3-Butadiene over Ceria Catalyst: A Molecular Insight

Distinctive redox properties and structural defects have made ceria a desirable choice for selective hydrogenation reactions for a wide array of hydrocarbons. In this work, we have studied – via density functional theory (DFT) calculations - selective hydrogenation of 1,3-butadiene into 1-butene over ceria catalyst. This reaction entails strategic applications in petroleum industries. Adsorption and surface energies for various co-adsorbed 1,3-butadaiene/hydrogen configurations were computed based on the ab initio atomistic thermodynamic formalism. The thermodynamically most stable configurations correspond to surfaces with high hydrogen surface coverage. This finding coincides with the commonly deployed high ratio of hydrogen to hydrocarbons in hydrogenation reactions over ceria. A consistent decrease in binding energies of multiple 1,3-butadiene adsorptions (per adsorbed molecule) is ascribed to a noticeable surface relaxation effects rather than to lateral interactions between adjacent adsorbed molecules. The partial hydrogenation route 1,3-butadiene →1-butene proceeds via accessible energy barriers and involves hydrogen transfer from OH* groups to surface-unbounded carbon sites. Desorption of the formed 1-butene constitutes a bottleneck in the partial hydrogenation route. The occurrence of full hydrogenation into n-butane is unfeasible in view of the high energy barrier encountered in the final hydrogen migration step to a surface-bounded carbon atom.