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On the stability of isolated iridium sites in N‐rich frameworks against agglomeration under reducing conditions

DOI: 10.1002/cctc.202200179 DOI Help

Authors: Andree Iemhoff (Rheinisch-Westfalische Technische Hochschule Aachen) , Maurice Vennewald (Rheinisch-Westfalische Technische Hochschule Aachen) , Jens Artz (Rheinisch-Westfalische Technische Hochschule Aachen) , Chalachew Mebrahtu (Rheinisch-Westfalische Technische Hochschule Aachen) , Alexander Meledin (Rheinisch-Westfalische Technische Hochschule Aachen) , Thomas E. Weirich (Rheinisch-Westfalische Technische Hochschule Aachen) , Heinrich Hartmann (Forschungszentrum Jülich GmbH) , Astrid Besmehn (Forschungszentrum Jülich GmbH) , Matteo Aramini (Diamond Light Source) , Federica Venturini (Diamond Light Source) , Fred Mosselmans (Diamond Light Source) , Georg Held (Diamond Light Source) , Rosa Arrigo (Diamond Light Source) , Regina Palkovits (RWTH Aachen University)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Chemcatchem

State: Published (Approved)
Published: March 2022
Diamond Proposal Number(s): 26053 , 26030

Abstract: Stabilization of single metal atoms is a persistent challenge in heterogeneous catalysis. Especially supported late transitions metals are prone to undergo agglomeration to nanoparticles under reducing conditions. In this study, nitrogen-rich covalent triazine frameworks (CTFs) are used to immobilize iridium complexes. Upon reduction at 400°C, immobilized Ir(acac)(COD) on CTF does not form nanoparticles but transforms into a highly active Ir single atom catalyst. The resulting catalyst systems outperforms both the immobilized complex and supported nanoparticles in the dehydrogenation of formic acid as probe reaction. This superior performance could be traced back to decisive changes of the coordination geometry positively influencing activity, selectivity and stability. Spectroscopic analysis reveals an increase of electron density on the cationic iridium site by donation from the CTF macroligand after removal of the organic ligand sphere from the Ir(acac)(COD) precursor complex upon reductive treatment. This work demonstrates the ability of nitrogen moieties to stabilize molecular metal species against agglomeration and opens avenues for catalysts design using isolated sites in high-temperature applications under reducing atmosphere.

Subject Areas: Chemistry

Instruments: B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS , I20-Scanning-X-ray spectroscopy (XAS/XES)

Added On: 31/03/2022 11:36

Discipline Tags:

Physical Chemistry Catalysis Chemistry

Technical Tags:

Spectroscopy X-ray Absorption Spectroscopy (XAS) Near Edge X-ray Absorption Fine Structures (NEXAFS)