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.