Evaluating Pd–Ni layered catalysts for selective hydrogenation of 1,3-butadiene: A theoretical perspective

• 13BD hydrogenation reaction pathways on two bimetallic Pd–Ni were studied.
• On both surfaces, the reaction pathway most favored is trough the 2B1R intermediate.
• The 13BD hydrogenation more favored thermodynamically occurred on Pd/Ni(1 1 1).
• On Pd/Ni(1 1 1), reaction products are mainly the butene isomers.

The partial hydrogenation of 1,3-butadiene (13BD) to several C4H8 products, including 1-butene (1B), 2-butene (2B) and butan-1,3-diyl (B13R), on both Pd/Ni(1 1 1) and Pd3/Ni(1 1 1) bimetallic surfaces was theoretically investigated using DFT methods. For that purpose, different intermediates C4H7 and C4H8 radical species were evaluated according to the Horiuti–Polanyi mechanism performed in two sequential steps. The whole process was found to be exothermic on Pd/Ni(1 1 1) and endothermic on Pd3/Ni(1 1 1). Furthermore, the former surface, where the intermediate adsorptions are more favorable, exhibits lower activation barriers than Pd3/Ni(1 1 1). On both surfaces, the B13R formation is associated with high transition state energies through the pathways studied here; for this reason, it is extremely improbable to obtain B13R. Our calculations predict that on the Pd/Ni(1 1 1) catalyst model, the products would be mainly the butene isomers, with a little more selectivity toward 2B, in contrast to the pure Pd surface and in agreement with experimental data.

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