This thesis utilizes synchrotron-based X-ray techniques, advanced data analysis methodologies, and theoretical calculations to comprehensively investigate the structural, electronic, and reactive properties of metal-organic frameworks (MOFs) under operando conditions. In the first study, the structural and catalytic properties of MIL-100(Fe) were explored. It was observed that MIL-100(Fe) forms open Fe(II) sites upon thermal activation, which can catalyze the methane-to-methanol (MTM) conversion using molecular oxygen. A combination of X-ray spectroscopy and diffraction techniques was employed to monitor multiple reaction cycles, providing insight into the possible reaction intermediates. DFT calculations were used to propose a reaction mechanism involving O2 and CH4 interactions with Fe(II) sites to form methanol, highlighting stages where methyl radical intermediates might escape, leading to catalyst deactivation. This study indicated that while MIL-100(Fe) shows some catalytic activity, it is limited for industrial MTM processes, prompting the need for more stable trimetallic iron-based MOFs. The second study focused on water adsorption/desorption mechanisms in Mg-MOF-74. A combination of theoretical MD calculations, AP-NEXAFS, and PXRD revealed how water adsorption causes significant structural changes in the MOF's unit cell, specifically expanding the a axis and contracting the c axis. A machine-learning analysis of NEXAFS data showed residual water adsorbed at high temperatures, even when a significant number of open Mg2+ sites are present. Further, a subsequent study highlighted that different metal ions in MOF-74 significantly influence water retention capabilities, with Mg-MOF-74 retaining more water at high temperatures compared to Co-MOF-74 and Ni-MOF-74. Finally, surface defect formation and reactivity in HKUST-1 were investigated using NEXAFS. It was shown that oxidative decarboxylation leads to defective Cu(I)/Cu(II) paddlewheels that can be restored by exposure to CO2. These findings demonstrate how integrating complementary X-ray techniques with theoretical models provides deep insights into MOF properties, enabling the optimization of MOF performance for industrial applications.

Probing the structure and reactivity of metal-organic frameworks in operando / Tofoni, Alessandro. - (2025 Jan 17).

Probing the structure and reactivity of metal-organic frameworks in operando

TOFONI, ALESSANDRO
17/01/2025

Abstract

This thesis utilizes synchrotron-based X-ray techniques, advanced data analysis methodologies, and theoretical calculations to comprehensively investigate the structural, electronic, and reactive properties of metal-organic frameworks (MOFs) under operando conditions. In the first study, the structural and catalytic properties of MIL-100(Fe) were explored. It was observed that MIL-100(Fe) forms open Fe(II) sites upon thermal activation, which can catalyze the methane-to-methanol (MTM) conversion using molecular oxygen. A combination of X-ray spectroscopy and diffraction techniques was employed to monitor multiple reaction cycles, providing insight into the possible reaction intermediates. DFT calculations were used to propose a reaction mechanism involving O2 and CH4 interactions with Fe(II) sites to form methanol, highlighting stages where methyl radical intermediates might escape, leading to catalyst deactivation. This study indicated that while MIL-100(Fe) shows some catalytic activity, it is limited for industrial MTM processes, prompting the need for more stable trimetallic iron-based MOFs. The second study focused on water adsorption/desorption mechanisms in Mg-MOF-74. A combination of theoretical MD calculations, AP-NEXAFS, and PXRD revealed how water adsorption causes significant structural changes in the MOF's unit cell, specifically expanding the a axis and contracting the c axis. A machine-learning analysis of NEXAFS data showed residual water adsorbed at high temperatures, even when a significant number of open Mg2+ sites are present. Further, a subsequent study highlighted that different metal ions in MOF-74 significantly influence water retention capabilities, with Mg-MOF-74 retaining more water at high temperatures compared to Co-MOF-74 and Ni-MOF-74. Finally, surface defect formation and reactivity in HKUST-1 were investigated using NEXAFS. It was shown that oxidative decarboxylation leads to defective Cu(I)/Cu(II) paddlewheels that can be restored by exposure to CO2. These findings demonstrate how integrating complementary X-ray techniques with theoretical models provides deep insights into MOF properties, enabling the optimization of MOF performance for industrial applications.
17-gen-2025
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11573/1732905
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