Selectivity control for the catalytic 1,3-butadiene hydrogenation on Pt(111) and Pd(111) surfaces: Radical versus closed-shell intermediates.

The hydrogenation of 1,3-butadiene to different C4H8 species on both Pd(111) and Pt(111) surfaces has been studied by means of periodic slabs and DFT. We report the adsorption structures for the various mono- and dihydrogenated butadiene intermediates adsorbed on both metal surfaces. Radical species are more clearly stabilized on Pt than on Pd. The different pathways leading to these radicals have been investigated and compared to those producing 1-butene and 2-butene species. On palladium, the formation of butenes seems to be clearly favored, in agreement with the high selectivity to butenes observed experimentally. In contrast, the formation of dihydrogenated radical species seems to be competitive with that of butenes on platinum, which could explain its poorer selectivity to butenes and the formation of butane as a primary product.