(134g) Water-Gas Shift Activity of Platinum Promoted by Alkali Ions
Alkali additives have been widely used as promoters for Pt based catalysts in industrial catalysts such as the synthesis of ammonia, automotive emission control, CO hydrogenation, and recently PROX and WGSR[ 2,3]. The presence of alkali ions (Na, K) added in small amounts significantly promotes the activity of platinum for the low-temperature WGS reaction. Remarkably, low content (<1 at%) platinum on various oxide supports modified by a small amount (1 ? 9 at%) of alkali metals shows catalytic performance comparable to Pt on ceria, the most ?active? support reported to date.
The introduction of alkali metals on the Pt- free or doped support changes the surface of the supports; it provides reducible surface oxygen at low temperatures (<200oC) and active OH groups (~150oC). On the other hand, alkali dopants suppress the sintering of Pt particles and maintain most of the Pt in oxidized state. The CO-Pt bond is weaker when Pt is more electron-deficient, thus CO is more active to involve in the reaction pathway. These findings, supported by DFT calculations, and detailed characterization of the active catalysts will be presented.
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