Study on Pt@SiO2 core-shell nanoparticle for high-temperature catalysis and its active site identification

Abstract

Metal nanoparticles with high surface to volume ratio and unique catalytic reactivity are dispersed on oxide supports and commonly used as a heterogeneous catalyst in many industries including automobile exhaust control and hydrocarbon reforming for fuel cells. For the ideal design of these catalysts, elemental and structural modification and related studies to maximize the catalytic activity and stability under reacting conditions are of great interest. However, despite academic and industrial demands, their application and fundamental research on high-temperature catalysis face obstacles, owing to the sintering behavior of the nano-sized metal particles.

In this thesis, monodispersed Pt nanoparticles with various particle diameters were synthesized through colloidal synthesis and then post-encapsulated with silica shell to give sintering resistance at high temperatures. Synthetic variables that affect the final morphology and quality of the core-shells were identified and various physical and chemical analyses were conducted by using transmission electron microscopy, X-ray diffraction, inductively coupled plasma spectroscopy and CO chemisorption. The catalytic activity of the $Pt @SiO_2$ core-shell nanoparticles was also measured for CO and $CH_4$ oxidation with varying core sizes, and the results were compared to $Pt/SiO_2$ reference particles in terms of reactivity and stability.

I observed that the $Pt@SiO_2$ is slightly less reactive to CO oxidation at low temperatures (<300°C) than $Pt/SiO_2$, but promotes $CH_4$ oxidation much more aggressively at higher temperatures (>550°C). However, non-negligible degradation of the core-shell catalyst was observed, and possible reasons were suggested. Finally, the metal surface was identified as the active site of the $Pt@SiO_2$ catalyst by studying the particle size effect. The results help us get a step closer to ideal design for a heterogeneous catalyst in high-temperature chemical reactions.