Understanding the Strong Metal - Support Interaction (SMSI) Effect in CuxNi1-x/CeO2 (0 < x < 1) Nanoparticles for Enhanced Catalysis

The strong metal support interaction (SMSI) effect plays a central role in catalysis by decreasing the catalytic activity or even improving it in some specific cases. In spite of the intense research, a detailed description of the SMSI effect in CeO2-based catalysts is still missing. In this work, CuxNi1-x/CeO2 (0 < x < 1) nanoparticles were exposed to a reduction treatment in a H-2 atmosphere followed by an oxidation treatment in a CO2 atmosphere, both at 500 degrees C, and studied by using state-of-the-art techniques (in situ time-resolved X-ray absorption near edge structure (XANES) and near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS)). It was observed the migration of Cu (Ni) atoms toward the surface of Cu-Ni bimetallic nanoparticles during reduction (oxidation) treatments. The core shell-like structure is dependent on the Cu/Ni ratio. It was observed the existence of a capping layer from the support (CeO2-x) surrounding the metallic nanoparticles after reduction treatment (characteristic of the SMSI effect) in some specific cases, depending on the Cu/Ni ratio as well. The surface of the nanoparticles presenting the SMSI effect is recovered to the initial state after exposure to the CO2 atmosphere. Moreover, the nature of the SMSI effect was elucidated. The capping layer interacts with the Cu and Ni atoms via Ce 3d(10) 2p(6) Ce 4f(0) and Ce 3d(10) 2p(6) Ce 4f(1) initial states, depending on the case studied. As a consequence of the SMSI effect, the Cu atoms of the nanoparticles reduce at lower temperature than similar nanoparticles that do not present the SMSI effect. Therefore, the decrease in reduction temperature is directly related to the interaction between the CeO2-x capping layer and Cu and Ni atoms.