Atomically Dispersed Palladium to Enhance the Propyne Semihydrogenation over CeO₂ Catalysts

Abstract

Metal oxides such as ceria (CeO2) have been emerging as promising catalysts for selective hydrogenation, but the intrinsic activity is still limited due to the unfavorable activation of hydrogen under mild conditions. Herein, we report anchoring atomically dispersed Pd atoms onto as-synthesized CeO2 nanorods (r-CeO2) to decorate the oxide catalyst toward enhanced propyne semihydrogenation. Detailed characterizations, including aberration-corrected scanning transmission electron microscopy with atomic resolution, X-ray photoelectron spectroscopy (XPS), and diffuse reflectance infrared Fourier transform spectroscopy of CO adsorption, reveal the successful anchoring of atomically dispersed Pd on CeO2 nanorods via a facile loading process. The catalytic tests show that the as-synthesized Pd0.1/r-CeO2 catalysts exhibit significantly increased hydrogenation activity as compared to the undecorated r-CeO2, and the selectivity to target propylene is achieved to 95.3% at full conversion of propyne at around 95 °C on the Pd0.1/CeO2 catalyst. XPS, electron paramagnetic resonance, and temperature-programmed reduction tests unravel that the atomically dispersed Pd species remarkably promote the formation of oxygen vacancies on the surface of r-CeO2, which is beneficial for H2 activation and subsequently propyne semihydrogenation.