Selective Partial Hydrogenation of 1,3-Butadiene to Butene on Pd(110): Specification of Reactant Adsorption States and Product Stability

Selective partial hydrogenation of 1,3-butadiene (C 4 H 6 ) to butene (C 4 H 8 ) on hydrogen-precovered Pd(110) has been investigated using temperature-programmed desorption (TPD), scanning tunneling microscopy (STM), and high-resolution electron energy loss spectroscopy (HREELS). Below room temperature, C 4 H 6 was molecularly chemisorbed on a hydrogen-precovered Pd(110) surface and was in the π-bonded chemisorption state. The hydrogenation of C 4 H 6 did not occur in the sparse domains of less than 0.25 ML. With increasing C 4 H 6 coverage, C 4 H 6 formed dense domains, and the π bond was weakened. Only the weakly π bonded C 4 H 6 was hydrogenated to C 4 H 8 at about 200 K. Because the stability of resultant C 4 H 8 was low on the surface at the reaction temperature, C 4 H 8 desorbed immediately after being produced or dehydrogenated to C 4 H 6 if even a part of the C 4 H 8 remained on the surface. We concluded that the balance between the hydrogenation reactivity of C 4 H 6 and the stability of C 4 H 8 leads to the partial hydrogenation on the Pd surface.