Single-atom Rh based bipyridine framework porous organic polymer: A high active and superb stable catalyst for heterogeneous methanol carbonylation

Abstract

A novel Rh based porous composed N polymer with hierarchical pore, high surface area and high thermal stability (Rh-POL-2BPY) was successfully obtained by impregnation of Rh2(CO)4Cl2 solution of dichloromethane. And based on Rh species as the most active carbonylation site, Rh-POL-2BPY was selected as a catalyst applied in heterogeneous methanol carbonylation system and behaved excellent carbonylation activity (TOF ≈ 1400 h−1) under 195 °C, 2.5 MPa, higher than the corresponding homogeneous system without acetic acid. In addition, contrast to the most reported unstable heterogeneous methanol carbonylation systems, Rh-POL-2BPY could maintain incredibly outstanding stability for near 400 h owing to the firm coordination bond between Rh and N and high exposed N content in the polymer. Here, POL-2BPY apart from its heat-resisting property acts as massive rivets to immobilize the Rh species in its framework solidly during carbonylation process. XPS, XANES, HAADF-STEM and EXAFS results verify the N species of bipyridine, the single atom dispersion of Rh and RhN coordination bond. And above all, the novel five-coordinated Rh center is proposed as the real active site of methanol carbonylation by EXAFS spectra.