Highly efficient acetylene semi-hydrogenation over Cun cluster stabilized Pd1 single-atom catalysts

The single-atom catalysts (SACs) with the maximum metal utilization efficiency exhibits the advantage of high ethylene selectivity compared with the cluster catalyst in the acetylene semi-hydrogenation reaction, however, the SACs also possess the disadvantages of poor activity and high-temperature stability. Thus, maintaining high reactivity and stability while achieving high ethylene selectivity faces a challenge. The coordination environment of the first metal atom is reasonably adjusted by coordinating with the second adjacent metal atom, which provides the possibility of stimulating the intrinsic reactivity of SACs and maintaining the atomic properties unchanged during the reaction. Here, we prepared Pd1-Cun/Al2O3 catalysts with palladium single-atom species (Pd1) and copper cluster species (Cun) loaded on Al2O3 support by combining “anchoring” and “site isolation”, which effectively prevented the Pd1 transition to Pd cluster species (Pdn) during the reaction process while improving the activity of Pd1. The reaction evaluation results revealed that the activity of the Pd1-Cun/Al2O3 catalyst increased by 60 % compared with the Pd1/Al2O3 catalyst, and the stabilization time of ethylene selectivity (83 %) of Pd1-Cun/Al2O3 catalyst increased by > 100 h when the same conversion for both catalysts. The aberration-corrected high-angle annular dark-field scanning transmission electron microscopic (AC-HAADF-STEM), Diffuse reflectance Fourier transform infrared spectroscopy of CO adsorption (CO-DRIFTS) and X-ray photoelectron spectroscopy (XPS) showed that the “synergistic effect” of Cun and Pd1 is the main reason for the increase of reactivity, and the “site isolation” effect of Cun is a key factor in preventing the transition of Pd1 to Pdn. This method provides new research ideas for improving the activity of SACS and inhibiting the agglomeration of active centers.