Journal
SCIENCE BULLETIN
Volume 65, Issue 20, Pages 1743-1751Publisher
ELSEVIER
DOI: 10.1016/j.scib.2020.06.020
Keywords
Metal single atom catalysts; Porphyrin-like sites; N-doped carbon; Metal organic frameworks; X-ray absorption spectroscopy
Categories
Funding
- Ministry of Business, Innovation and Employment Catalyst Fund [MAUX 1609]
- University of Auckland Faculty Research Development Fund
- MacDiarmid Institute for Advanced Materials and Nanotechnology
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The pyrolysis of zeolitic imidazolate frameworks (ZIFs) 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 degrees C. 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 degrees C. As the pyrolysis temperature increased in the range 600-900 degrees C, the Zn atoms moved closer to the N-4 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 H2O2. The catalyst obtained at 800 degrees C (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. (C) 2020 Science China Press. Published by Elsevier B.V. and Science China Press. All rights reserved.
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