In-situ study of the process of adsorption/desorption of gaseous molecules on supported atomic quantum clusters

JORI, KHALIL; FELIX REQUEJO; JOSE MARTIN RAMALLO LOPEZ

Campinas

Encuentro; 29th Annual Users? Meeting (RAU); 2019

CNPEM

Atomic Quantum Clusters (AQC) are particles with well-defined structures and composition having a lownumber of atoms, below approximately 150 (<≈1.7 nm in size). The behavior of such clusters is differentfrom nanoparticles of larger sizes because their sizes are comparable to the Fermi wavelength of theelectrons (approx. 2 nm in Au, Ag or Cu). One of the main features of AQC is that the surface plasmonresonance – typical in metallic particles – disappears since all cluster electrons are covalently bonded [1].Secondly, a band gap appears giving rise to semiconductor like (or molecular-like) properties, such asphotoluminescence which is one of the most studied properties in metal clusters. This property of AQCmakes them candidates for many applications, particularly in areas such as catalysis and photocatalysis[2].In order to fabricate new efficient systems that can reach the industry and actual application, we need to testhow these entities react with the environment, especially when supported on different substrates andexposed to different atmospheres, temperatures or external conditions, and study how these conditions canmodify the AQCs electronic and physicochemical properties [3]. In this work, we performed a local structuralcharacterization of Cu5 AQC clusters using X-ray Absorption Fine Structure Spectroscopy at the Cu-K edgein different conditions to understand their potential application for catalysis. In particular we characterizedCu5 AQC supported on different types of materials than can be interesting for the catalysis industry (Al2O3,SBA, TiO2, ZrO2, Graphite, etc.) in order to study their interaction with the different supports and determinehow their electronic properties are modified by this interaction. Then, we studied the adsorption/desorptioncapacity of CO, O2 and H2 molecules at different temperatures on Cu5 supported on graphite, in order touse them as an active phase of catalysts for oxidation and hydrogenation reactions