(108f) Na-Promoted Pt Catalysts In Core-Shell Structure for the Low-Temperature Water-Gas-Shift Reaction

The water-gas-shift (WGS) reaction is a key step in high-purity hydrogen production. Platinum-based catalysts are active over a wide temperature range and stable during operation cycles. Pt on reducible ceria is a highly active catalyst for the low-temperature WGS reaction, while Pt on irreducible silica or alumina is a poor shift catalyst. We recently reported that a small amount of sodium ions can activate platinum-based catalysts on irreducible oxides, such as silica and alumina, for the low-temperature WGS reaction, even better than Pt on ceria. Here we introduce new core-shell structured catalyst Pt@SiO₂ to further the study in WGS kinetics and mechanism.

The core-shell structured catalyst Pt at silica was synthesized by reverse microemulsion (ME) approach. Alkali ions were added by impregnation after preparation. In addition to the Pt core, platinum is atomically dispersed throughout the silica shell and sodium ions stabilize the atomically dispersed platinum species in the support. Cyclic CO-TPR tests show that water activation and hydroxyl regeneration take place on sodium associated Pt sites. In contrast, surface hydroxyl groups cannot be recovered on sodium-free sample after reaction with CO.

The sodium ion–associated surface hydroxyl groups are activated by CO at low temperatures (~120°C) in the presence of atomically dispersed platinum. The alkali species on the catalysts can stabilize the dispersed Pt atoms and regenerate surface hydroxyl groups. As a result, a partially oxidized Pt-OH_x species associated with alkali ions is the active site for the low-temperature WGS reaction.