Controlling the speciation and selectivity of Si3N4 supported palladium nanostructures for catalysed acetylene selective hydrogenation

Metal-support interactions predominately determine the electronic structure and catalytic behavior of metal nanoparticles. However, direct tuning of the metal-support interaction under mild conditions and directional regulation of the surface charge remain challenging. Herein, we describe the transformation of Pd species in Pd/Si3N4 catalysts under facile thermal activation conditions to control the selectivity of acetylene hydrogenation. Specifically, after thermal activation, a series of flattened Pd particles with different convexities were formed, driving the formation of low-coordination Pd-N-x and Pd delta- species, thus providing a more reactive Pd delta- surface and a more stable Pd delta+-N-x interface (Pd delta-@Pd delta+-N-x). Such a structure hinders Pd hydride formation and weakens ethane adsorption, and thus improves the catalytic performance and stability for acetylene semi-hydrogenation. The surface of the low-convexity Pd particles with a denser and richer Pd delta- capping layer exhibits a lower differential adsorption energy, |E-ads(C2H2) - E-ads(C2H4)|, resulting in a higher ethylene selectivity. Moreover, the combination of high-resolution transmission electron microscopy (HR-TEM), infrared Fourier transform spectroscopy of adsorbed CO (CO-FTIR), X-ray absorption spectroscopy (XAS), and X-ray photoelectron spectroscopy (XPS) demonstrated that different active sites play distinct roles in this catalytic reaction, where the charge of the surface Pd delta- species determines the catalytic activity and selectivity, and the content of Pd-N-x regulates the catalyst stability.

Automated summary

Metal-support interactions are crucial for the catalytic behavior of metal nanoparticles. In this study, we demonstrate the transformation of Pd species in Pd/Si3N4 catalysts under mild thermal activation conditions, which leads to improved catalytic performance and selectivity for acetylene hydrogenation.