Prof. Félix G. Requejo: Cu5 and Ag5 subnanometer clusters in catalysis: XANES spectroscopy studies

Nanocatalysis Department Seminar
Wednesday, September 17, 2025, 13:00h
J. Heyrovský Institute, Seminar Room 108

Abstract
Subnanometer metal clusters composed of only a few atoms exhibit unique properties that make them highly attractive for catalysis. In this presentation, we will discuss recent advances in the study of five-atom copper and silver clusters (Cu₅ and Ag₅), emphasizing their catalytic performance as revealed by operando X-ray absorption near-edge structure (XANES) spectroscopy. Ag₅ clusters have demonstrated remarkable activity in the complete oxidation of sulfur-containing compounds, including dibenzothiophene and other highly resistant thiophenes, under ambient conditions, offering a simple and green route for fuel desulfurization. On the other hand, Cu₅ clusters supported on TiO₂ display exceptional selectivity and efficiency in CO₂ methanation, reaching 100% selectivity toward CH₄ at only 300 °C, with low activation energy, and their performance has been rationalized through combined operando XANES and DFT studies. In both cases, XANES spectroscopy provided crucial insights into the oxidation state dynamics and reaction pathways, highlighting the reversible redox behavior of Cu₅ in CO₂ hydrogenation and the oxidation routes promoted by Ag₅ in sulfur removal. Together, these findings illustrate the potential of subnanometer clusters as efficient, stable, and environmentally relevant catalysts, while underscoring the power of XANES spectroscopy to unravel their structure–activity relationships under reaction conditions.

Félix Requejo is a Professor in the Department of Physics at the Faculty of Science, National University of La Plata, and Director of the Institute of Theoretical and Applied Physicochemical Research (INIFTA, UNLP/CONICET). He obtained his B.S. degree from UNLP in 1987 and his Ph.D. in Physics from the same institution in 1993, followed by postdoctoral training at the Materials Science Division and the Advanced Light Source, Lawrence Berkeley National Laboratory (2000–2003). He leads a dynamic research group focused on advanced techniques employing X-ray sources across diverse scientific fields. He has authored more than 120 peer-reviewed publications, with over 6,000 citations and an H-index of 42. His contributions have been recognized with awards in Nanotechnology and Physicochemistry from Argentine institutions.