Preparation of Pd-ZIF-8 single-atom catalyst with supercritical CO2 deposition method

Abstract

In recent years, single-atom catalysts (SAC) have emerged as a new frontier in the field of heterogeneous catalysis owing to their unique properties and minimized metal dosage. Herein, the Pd-ZIF-8 single-atom catalyst was successfully fabricated using ZIF-8 as support, and Pd(hfac)2 as the precursor using the supercritical CO2 deposition method. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM) images confirmed the formation of uniformly dispersed Pd atoms. Supercritical CO2 has the advantage of zero-surface tension and high diffusibility, it can carry the molecules of Pd precursor into the micropores of ZIF-8. The dissolution and diffusion of precursor were observed by a visual view cell and the mechanism of the preparation was analyzed. Finally, semi-hydrogenation of phenylacetylene to styrene was performed to evaluate the catalytic activity of the prepared Pd-ZIF-8 catalyst. The conversion rate of 80.7% and selectivity of 92.2% were obtained at 70 °C and 4 h in the semi-hydrogenation of phenylacetylene.