Morphology Control of Platinum Nanoparticles and their Catalytic Properties

Platinum nanoparticles with different morphology were prepared by reduction of K₂PtCl₄ solution in the presence of different capping polymers. It was found that the shapes and the sizes of the Pt nanocrystals resulted were related to the kind of capping polymer used. When poly(vinylpyrrolidon) (PVP), poly(N-isopropylacrylamide) (NIPA) and sodium poly(acrylate) (SPA) were used as capping agents, the dominant shapes of the Pt nanocrystals observed by transmission electron microscopy were hexagonal (62%), square (67%) and triangular (41%), respectively. The average sizes of Pt nanocrystals were 6.9, 13.6 and 14.6 nm for capping polymers of PVP, NIPA and SPA, respectively. The colloidal Pt nanoparticles with different morphologies were supported on -Al₂O₃ (1 wt.% Pt) and then their catalytic activity for NO reduction by CH₄ was tested in the 350–600°C temperature range. Additionally, the catalytic activities of these alumina-supported Pt nanocrystals were compared with a conventional catalyst having the average size of Pt particles of 2.4 nm. Over the alumina-supported Pt nanocrystals as compared with the conventional Pt/Al₂O₃, it was observed that the NO/CH₄ reaction yields to NH₃ and CO decreased significantly and on the other hand, the yield to N₂O increased. The experimental results are suggesting that the catalytic behavior can be tuned in a convenient way through the morphological control of the metal nanoparticles.