Ionic liquid overlayers stabilize ligand-coordinated oxide-supported single-atom Pd heterogeneous catalysts for...

Single atom catalysts offer promising mechanisms for highly selective hydrocarbon conversions in heterogeneous catalysts that can be scaled up to address industrially-relevant challenges. Stability of the catalysts is critical, not just because of the need to maintain high conversion for long time periods, but also to maintain the precise single-atom environment that facilitates high reaction selectivity. We have demonstrated a ligand-coordination strategy for oxide-supported single atom Pd catalysts and, in this work, we demonstrate that ultrathin ionic liquid overlayers add significant stability to the catalysts. These catalysts can be synthesized with single-atom character at loadings as high as 0.8 wt% Pd and are effective for selective partial hydrogenation of acetylene to ethylene, as demonstrated by flow reactor experiments. The addition of the ionic liquid overlayer enables a wider operational range of temperature and provides increased resistance against sintering. The ionic liquids do not hinder the C₂ molecule access to the Pd active sites, but they do enable improved reaction selectivity. The dynamic interface of ionic liquid and cerium oxide provides an outstanding environment for Pd coordination to small organic ligands that define a highly effective Pd(II) species for selective hydrogenation.