Supported, ∼1-nm-Sized Platinum Clusters: Controlled Preparation and Enhanced Catalytic Activity

Abstract

We have been aiming to reduce the amount of platinum (Pt) needed in catalysts for automobile exhaust-gas purification and fuel cell electrodes. To achieve this, we have attempted to: 1) establish simple methods for synthesizing ligand-protected ~1-nm-sized Pt clusters with a narrow distribution in the number of constituent atoms; 2) load these clusters onto supports, while retaining their number of constituent atoms, to prepare supported ~1-nm-sized Pt clusters; and 3) elucidate the catalytic activity of each type of supported ~1-nm-sized Pt cluster. These studies have revealed that: 1) ligand-protected ~1-nm-sized Pt clusters stable in the atmosphere can be isolated with high purity by a combination of polyol reduction and ligand-exchange reaction; 2) ~1-nm-sized Pt clusters can be loaded onto the support without aggregation when the clusters are adsorbed on the support and then calcined at an appropriate temperature; and 3) Pt₁₇ clusters loaded onto γ-alumina exhibit high activity and durability for exhaust-gas purification, whereas Pt_n clusters (n = ~35, ~51, or ~66) loaded onto carbon black exhibit high activity and durability for the oxygen reduction reaction (which occurs at fuel cell electrodes). This account describes our previous studies and explores future prospects for supported ~1-nm-sized Pt clusters.