In situ preparation of Ni-Cu/TiO2 bimetallic catalysts

A nanoscale investigation was performed on the initial stages of the formation of nanoparticles during the preparation of NiCu/TiO2 bimetallic catalysts by incipient wetness impregnation. The evolution of the structure and chemistry of individual nanoparticles was followed in the reaction cell of an environmental transmission electron microscope. During reduction in hydrogen at 300 degrees C, nuclei quickly formed and grew mainly via Ostwald ripening or short-range particle-particle coalescence. The presence of Cu greatly enhanced the reducibility of the Ni species and about 85% of the particles were metallic. Most of the particles were uniform in composition but approximately 15% of the particles showed Ni enrichment on the surface. The surface enrichment of Ni was attributed to differential diffusion processes and demonstrated that, for the reduction temperature used for this experiment, the structure of the bimetallic particles was controlled by kinetics rather than by thermodynamics. (C) 2008 Elsevier Inc. All rights reserved.