Nanocrystal Dispersed Platinum Particles: Preparation and Catalytic Properties
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The synthesis of metal particles with well-controlled shapes and sizes is critical for catalytic applications in structure-sensitive reactions because the rates depend significantly on the metal crystallite size as well as on the orientation of the crystalline planes. The morphology–catalytic reactivity relationship is generally unclear for the catalysts prepared by classical impregnation method because the resulting metal particles are nonuniform in size and shape, and are often too small to be precisely characterized. Additionally, there is a significant support effect on the catalytic reactivity of the small metal particles. With other preparation methods such as vapor and metal cluster deposition, electron beam lithography, etc., it is possible to control, to some extent, the size, but not the crystallographic orientation, of the metal particles.
The colloid method is one of the most promising ways to obtain relatively monodispersed metal particles with controlled shapes. Among metals, platinum is a suitable precursor because different shapes of nanoparticles can be prepared by using suitable capping polymers. The NO/CH4 reaction was chosen to investigate the structure–catalytic reactivity relationship for the well-structured Pt nanoparticles. The conventionally prepared Pt/Al2O3 catalysts give relatively high selectivity to NH3 and CO. Because NO/CH4 reaction is structure-sensitive, significant improvements in the catalytic behavior are expected through a fine control of the morphology of Pt particles.
The general aim of our work is to bridge the gap existing between the science of clean single crystals surfaces and the world of real catalysis. Particularly, we intend to have a better understanding of the relationship existing between the structure of the supported Pt particles and the catalytic behavior for the NO/CH4 reaction. From the practical point of view, our scope is to prevent or to considerably reduce the formation of undesired reaction products, such as NH3, CO, and N2O. The approach to fulfill the abovementioned goals was to prepare well-defined Pt nanocrystals having mainly cubic structure, to support them on alumina, and to test their specific catalytic activity for the NO/CH4 reaction.