Enhancing alkyne semi-hydrogenation through engineering metal-support interactions of Pd on oxides

Supported Pd catalysts show superior activities for olefin productions from alkynes through semi-hydrogenation reactions, but over-hydrogenation into alkanes highly decreases olefin selectivity. Using phenylacetylene semi-hydrogenation as a model reaction, here we explore the optimization approaches toward better Pd catalysts for alkyne semi-hydrogenation through investigating support effect and metal–support interactions. The results show that the states of Pd with supports can be tuned by varying oxide reducibility, loading ratios, and post-treatments. In our system, 0.06 wt.% Pd on rutile-TiO2 nanorods shows the highest activity owing to the synergistic effects of single-atoms and clusters. Support reducibility can change the filling degrees of Pd 4d orbitals through varying interfacial bonding strengths, which further affect catalytic activity and selectivity.