Heterogeneous catalysis is the workhorse of the chemical industry. In order to achieve genuine breakthroughs in catalyst development, it is crucial to unravel the structural/electronic nature of the active sites and to establish structure-catalytic performance relationships. Thus, molecular level understanding of the active site and the catalytic process is essential to develop next-generation catalysts. Synchrotron radiation has been widely applied in materials science, chemistry, chemical engineering and, particularly, catalysis. Synchrotron-based methods such as X-ray absorption fine structure spectroscopy (XAFS) can provide unique information to elucidate the structural/electronic properties of the catalytic active sites, even where other techniques fail. In this contribution, two recent catalyst studies conducted at XAFCA beamline will be discussed: i- Elucidating the structure of nickel hydroxide nano-ribbons for efficient water splitting using Synchrotron XAFS & XRD, STEM HAADF and DFT simulations. In this work, the first stabilized non-stoichiometric Ni(OH)2 nanoribbons with alternating 4- and 6- coordinated Ni edge atoms (NR-Ni(OH)2) was reported and operando XAFS was a key technique to reveal the formation of NR-Ni(OH)2 and NR-NiOOH ii- Understanding the nature of the of the active site for enhanced CO2 conversion to Methanol. In this example, hierarchically multi-voids mesoporous silica spheres (MVmSiO2) as a highly efficient maze-like support for metal nanoparticles. XAFS characterization, both ex-situ and in-situ, was a powerful technique to unravel the state of Cu during and after reaction. While Cu oxidizes to Cu2+ under pure CO2, it remains mostly reduced under the reaction mixture (i.e., H2/CO2) at the reaction temperature.

Unravelling the structural/electronic properties of heterogeneous catalysts using synchrotron-based techniques

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ACS Fall 2022

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