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 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℃.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 H2 O2.The catalyst obtained at 800℃(Zn-N-C-800) offered the best performance for H2 O2 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.展开更多
基金supported by the Ministry of Business, Innovation and Employment Catalyst Fund (MAUX 1609)the University of Auckland Faculty Research Development Fund+1 种基金the MacDiarmid Institute for Advanced Materials and Nanotechnologya generous philanthropic donation from Greg and Kathryn Trounson。
文摘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℃.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 H2 O2.The catalyst obtained at 800℃(Zn-N-C-800) offered the best performance for H2 O2 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.
