Catalytically active Au-O(OH)x- species stabilized by alkali ions on zeolites and mesoporous oxides

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Science  19 Dec 2014:
Vol. 346, Issue 6216, pp. 1498-1501
DOI: 10.1126/science.1260526

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We report that the addition of alkali ions (sodium or potassium) to gold on KLTL-zeolite and mesoporous MCM-41 silica stabilizes mononuclear gold in Au-O(OH)x-(Na or K) ensembles. This single-site gold species is active for the low-temperature (<200°C) water-gas shift (WGS) reaction. Unexpectedly, gold is thus similar to platinum in creating –O linkages with more than eight alkali ions and establishing an active site on various supports. The intrinsic activity of the single-site gold species is the same on irreducible supports as on reducible ceria, iron oxide, and titania supports, apparently all sharing a common, similarly structured gold active site. This finding paves the way for using earth-abundant supports to disperse and stabilize precious metal atoms with alkali additives for the WGS and potentially other fuel-processing reactions.

Dispersing catalytic gold as widely as possible

In order to maximize the activity of precious metals in catalysis, it is important to place the metal on some support with a high surface area (such as a zeolite) and to maintain the metal as small clusters or even atoms to expose as much metal as possible. The latter goal is more readily achieved with oxides of reducible metals such as cerium or titanium than with the aluminum and silicon oxides that make up most zeolites and mesoporous oxides. Yang et al. show that sodium and potassium can stabilize gold along with hydroxyl and oxo groups to create highly active catalysts for the water-gas shift reaction at low temperatures, a reaction that can be useful in applications such as fuel cells.

Science, this issue p. 1498

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