Heterogeneous Catalytic Transfer Partial-Hydrogenation with Formic Acid as Hydrogen Source Over the Schiff-Base Modified Gold Nano-Catalyst

Abstract

The catalytic hydrogenation transformation with gaseous hydrogen in liquid phase always refers to a harsh condition and over-hydrogenation, and it is highly desired to develop new methods with partial-hydrogenation at mild condition. Herein, a heterogeneous catalytic transfer partial-hydrogenation strategy with formic acid as hydrogen source was developed over the Schiff-base modified gold nano-catalysts. The Au/Schiff-SiO2 catalyst was successfully prepared by one pot aldimine condensation and NaBH4 reduction of a gold precursor. The characterization results indicated that the gold nanoparticles with an average size below 2 nm were highly dispersed over the Schiff-base modified silica support. Such Schiff-based gold nano-catalysts exhibits excellent activity and partial-hydrogenation selectivity, with a high yield (>99%) for phenylacetylene partial-hydrogenation and achieving a 75% chemoselectivity for imines at a relative low temperature and atmospheric pressure. More importantly, the excess of formic acid can be removed by the direct dissociation of formic acid over Au/Schiff-SiO2 catalyst with CO2 emission into atmosphere, which leads to a hydrogen source as clean as hydrogen gaseous, but with a much more high activity and selectivity under mild reaction process.