Evolution of Zn(Ⅱ) single atom catalyst sites during the pyrolysis-induced transformation of ZIF-8 to N-doped carbons

• 作者: Dongxiao Sun-Waterhouse Fanfei Sun Geoffrey I.N.Waterhouse Lu Shang Qing Wang Shane G.Telfer Shanghai Wei Tierui Zhang Toshiaki Ina Wan-Ting Chen
• 来源期刊: 科学通报（英文版）
• 年，卷（期）: 2020,（20）
• 所属期刊栏目: ARTICLES
• 页码范围: 1743-1751
• 页数: 9页
• 语种: 英文

摘要

The pyrolysis of zeolitic imidazolate frameworks (ZlFs) is becoming a popular approach for the synthesis of catalysts comprising porphyrin-like metal single atom catalysts (SACs) on N-doped carbons (M-N-C).Understanding the structural evolution of M-N-C as a function of ZIF pyrolysis temperature is important for realizing high performance catalysts.Herein,we report a detailed investigation of the evolution of Zn single atom catalyst sites during the pyrolysis of ZIF-8 at temperatures ranging from 500 to 900 ℃.Results from Zn L-edge and Zn K-edge X-ray absorption spectroscopy studies reveal that tetrahedral ZnN4 centers in ZIF-8 transform to porphyrin-like ZnN4 centers supported on N-doped carbon at temperatures as low as 600 ℃.As the pyrolysis temperature increased in the range 600-900 ℃,the Zn atoms moved closer to the N4 coordination plane.This subtle geometry change in the ZnN4 sites alters the electron density on the Zn atoms (formally Zn2+),strongly impacting the catalytic performance for the peroxidase-like decomposition of H202.The catalyst obtained at 800 ℃ (Zn-N-C-800) offered the best performance for H2O2 decomposition.This work provides valuable new insights about the evolution of porphyrin-like single metal sites on N-doped carbons from ZIF precursors and the factors influencing SAC activity.