Alkyne Hydrogenation Catalysis across a Family of Ga/In Layered Zintl Phases

Transition-metal-free Zintl–Klemm phases have received little attention as heterogeneous catalysis. Here, we show that a large family of structurally and electronically similar layered Zintl–Klemm phases built from honeycomb layers of group 13 triel (Tr) or group 14 tetrel (Tt) networks separated by electropositive cations (A) and having a stoichiometry of ATr₂ or ATrTt (A = Ca, Ba, Y, La, Eu; Tr = Ga, In; Tt = Si, Ge) exhibit varying degrees of activity for the hydrogenation of phenylacetylene to styrene and ethylbenzene at 51 bar H₂ and 40–100 °C across a variety of solvents. The most active catalysts contain Ga with, formally, a half-filled p_z orbital, and minimal bonding between neighboring Tr₂ or TrTt layers. A 13-layer trigonal polytype of CaGaGe (13T-CaGaGe) was the most active, cyclable, and robust catalyst and under modest conditions (1 atm H₂, 40 °C) had a surface specific activity (590 h^–1) comparable to a commercial Lindlar’s catalyst. Additionally, 13T-CaGaGe maintained 100% conversion of phenylacetylene to styrene at 51 bar H₂, even after 5 months of air exposure. This work reveals the structural design elements that lead to particularly high catalytic activity in Zintl–Klemm phases, further establishing them as a promising materials platform for hydrogen-based heterogeneous catalysis.