Constructing Efficient Single Rh Sites on Activated Carbon via Surface Carbonyl Groups for Methanol Carbonylation
Siquan Feng, Xiangsong Lin, Xiangen Song, Bingbao Mei, Jiali Mu, Jingwei Li, Yang Liu, Zheng Jiang, Yunjie Ding
Abstract
Heterogeneous single-metal-site catalysts have been drawing increasing interests in the field of academy and industry because of the comparable catalytic activity with homogeneous catalyst and easy separation. Here, an efficiently heterogeneous single-site Rh catalyst on activated carbon (Rh1/AC) was constructed, which performs three times activity than the corresponding homogeneous catalyst for methanol carbonylation. Experimental data reveals that the apparent activation energy on the Rh1/AC catalyst is 0.91 eV, far less than 1.54 eV of its homogeneous counterpart. Ex situ EXAFS confirms the molecular configuration of a single Rh site. DFT calculation demonstrates that the electron-donating carbonyl group on the surface of the support possesses the precedence to accommodate the single-site Rh ions. Furthermore, difference charge density verifies that the coordinative bond between a single metal ion and a carbonyl group enhances the electronic density of the central Rh atom, consequently lowering the energy barrier of the rate-determining step of CH3I oxidative addition. Together with the atomic dispersion, as well as the electronic interaction between a single Rh ion and carbonyl groups, the Rh1/AC catalyst performs superior activity than homogeneous systems.