General Strategy toward Hydrophilic Single Atom Catalysts for Efficient Selective Hydrogenation

Abstract

Well dispersible and stable single atom catalysts (SACs) with hydrophilic features are highly desirable for selective hydrogenation reactions in hydrophilic solvents towards important chemicals and pharmaceutical intermediates. A general strategy is reported for the fabrication of hydrophilic SACs by cation-exchange approach. The cation-exchange between metal ions (M = Ni, Fe, Co, Cu) and Na⁺ ions introduced in the skeleton of metal oxide (TiO₂ or ZrO₂ ) nanoshells plays the key role in forming M₁ /TiO₂ and M₁ /ZrO₂ SACs, which efficiently prevents the aggregation of the exchanged metal ions. The as-obtained SACs are highly dispersible and stable in hydrophilic solvents including alcohol and water, which greatly facilitates the catalysis reaction in alcohol. The Ni₁ /TiO₂ SACs have been successfully utilized as catalysts for the selective C=C hydrogenation of cinnamaldehyde to produce phenylpropanal with 98% conversion, over 90% selectivity, good recyclability, and a turnover frequency (TOF) of 102 h^-1 , overwhelming most reported catalysts including noble metal catalysts.

Keywords: cation-exchange; hydrophilicity; selective hydrogenation; single atom catalysts.