Structural Evolution of PdCu and PtCu Nanocrystal Catalysts over Redox Treatments

This thesis presents the main results on the synthesis of PdCu and PtCu bimetallic nanocrystals (NCs) and their application as catalysts for CO oxidation as a probe reaction. Focusing on Cu and keeping constant the NC size and the support material, the role of the noble metal in the alloy/dealloy/migration process of noble metal-Cu alloyed NCs was studied. The role of the support material in the same transformations was also objected of study. NCs with defined size and composition were successfully synthesized by means of colloidal synthesis methods. The NCs were further deposited on a SiO2 support and studies of catalytic activity were performed on NCs exposed to oxidizing and reducing pre-treatments before each catalytic test. The catalytic activity data were also collected on γ-Al2O3 support to investigate the correlation between the activity and the structural properties of such NCs. For this purpose, different analysis techniques were used as routine ex situ methods to characterize these materials. In situ methods such as diffuse reflectance infrared Fourier transform spectroscopy and X-ray absorption fine structure spectroscopy were used to monitor the structure evolution of the metals under controlled conditions. The use of in situ and operando methods has significantly highlighted that the structure of the metallic particles can be dramatically modified under reaction conditions in terms of geometry and chemical composition. The analysis and synthesis techniques and the main results obtained on structural changes in the NC catalysts under different conditions are widely described.