Pd/Co3O4–Pd/PdO formed in situ on the surface of the self-assembly ferrocenylimine Pd(ii)/Co(ii) monolayer for catalyzing the Suzuki cross-coupling reaction—formation, synergistic effect, and catalytic mechanism

Abstract

Understanding the structure of the real catalytic active centre is a key factor to design a highly efficient catalyst and elucidate the mechanism of catalysis. Herein, graphene oxide supported ferrocenyl imine Pd/Co film was designed and prepared by self-assembly (GO@APTES-Fcl-Pd_x/Co_1−x) and characterized by water contact angle (WCA), scanning electronic microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy (RS), Brunauer–Emmett–Teller (BET), Fourier transform infrared spectroscopy (FT-IR), and electrochemical impedance spectroscopy (EIS) mesaurements. The GO@APTES-Fcl-Pd_0.1Co_0.9 film was used to catalyze the Suzuki cross-coupling reaction with a high activity (TOF, 11 353 h⁻¹) and could be recycled at least 8 times. The heterogeneous catalytic mechanism was confirmed, and the real catalytic centres contained Pd, Pd/PdO, Pd/Co₃O₄(CoO/Co₂O₃), and Pd/PdO/Co₃O₄(CoO/Co₂O₃) clusters, in which Pd/Co₃O₄(CoO/Co₂O₃) as the main active species had the efficient synergistic effect between Pd and Co₃O₄ acted as the redox species, stabilizer, and support. Meanwhile, the ligand, organometallics, and carrier played an important role as the resource, stabilizer for the active centre, and in electron transfer from support to metals. The deactivation mechanism for the catalyst was mainly induced by the active center aggregation and the different facets of cobalt oxides formed during catalysis.