Transition Metal-Free Alkyne Hydrogenation Catalysis with BaGa₂, a Hydrogen Absorbing Layered Zintl Phase

Inexpensive, transition metal-free intermetallic compounds have received almost no attention as heterogeneous catalysts. Here, we show that BaGa₂, a Zintl-Klemm compound composed of honeycomb sheets of Ga^- anions separated by Ba²⁺ cations and known to react with H₂ under moderate conditions to form a layered polyanionic hydride BaGa₂H₂, effectively catalyzes the hydrogenation of phenylacetylene into styrene and ethylbenzene under modest conditions (1-50 bar H₂, 40-100 °C). Remarkably, the catalytic activity of BaGa₂ (surface specific activities up to 8390 h^-1) is on the same order of magnitude as commercial Pd-based catalysts. In contrast, BaGa₂H₂ shows negligible catalytic activity, thereby indicating that the unsaturated Ga^- framework is necessary for phenylacetylene and styrene adsorption. These findings open up future explorations of utilizing and optimizing the long-term stability of transition metal-free intermetallic hydrogen absorbing compounds for hydrogen-based catalysis.