Silvia Mauri's doctoral research activity is mainly focused on the investigation of the surface reactivity of heterogeneous catalysts by operando X-ray absorption spectroscopy with synchrotron radiation. Moreover, she performs computational simulations with DFT and semi-empirical methods, in order to have a clear and complete interpretation of the experimental data.
In this work, we apply for the first time ambient pressure operando soft X-ray absorption spectroscopy (XAS) to investigate the location, structural properties, and reactivity of the defective sites present in the prototypical metal–organic framework HKUST-1. We obtained direct evidence that Cu+ defective sites form upon temperature treatment of the powdered form of HKUST-1 at 160 °C and that they are largely distributed on the material surface. Further, a thorough structural characterization of the Cu+/Cu2+ dimeric complexes arising from the temperature-induced dehydration/decarboxylation of the pristine Cu2+/Cu2+ paddlewheel units is reported. In addition to characterizing the surface defects, we demonstrate that CO2 may be reversibly adsorbed and desorbed from the surface defective Cu+/Cu2+ sites. These findings show that ambient pressure soft-XAS, combined with state-of-the-art theoretical calculations, allowed us to shed light on the mechanism involving the decarboxylation of the paddlewheel units on the surface to yield Cu+/Cu2+ complexes and their reversible restoration upon exposure to gaseous CO2.
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NFFA is a Progetto Internazionale financed by MIUR through CNR
(Istituto Officina dei Materiali, Trieste) and Elettra-Sincrotrone Trieste
and managed by the Commissione NFFA chaired by Giorgio Rossi
(Università di Milano and IOM-CNR).