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Synthesis

Alkali Metal Aids Catalysis

The water-gas shift reaction can be catalyzed at lower cost by platinum aided by an alkali-metal promoter

by Jyllian N. Kemsley
September 27, 2010 | A version of this story appeared in Volume 88, Issue 39

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Credit: Maria Flytzani-Stephanopoulos
Platinum combines with potassium to produce PtK6O4(OH)2, which catalyzes the conversion of CO and H2O to CO2 and H2.M
Credit: Maria Flytzani-Stephanopoulos
Platinum combines with potassium to produce PtK6O4(OH)2, which catalyzes the conversion of CO and H2O to CO2 and H2.M

The water-gas shift reaction can be catalyzed by platinum dispersed on an inert support aided by an alkali-metal promoter, with Pt-alkali-Ox(OH)y as the key catalytic species, reports a group led by Maria Flytzani-Stephanopoulos of Tufts University and Manos Mavrikakis of the University of Wisconsin, Madison (Science 2010, 329, 1633). The reaction, which converts H2O and CO to H2 and CO2, is used to remove contaminant CO from H2 produced during fuel reforming. To replace air-sensitive and difficult-to-handle conventional catalysts, scientists have looked at catalyzing the reaction with Pt metal dispersed on titania, zirconia, or ceria, all of which can be catalytically promoted by the addition of alkali metals such as sodium and potassium. In the new work, the researchers instead investigated Pt on alkali-promoted alumina and silica, which are less expensive, and found catalytic activity comparable to Pt on ceria. They believe the catalytically active species is an oxidized, nonmetallic form of Pt and that the alkali-metal component prevents agglomeration and inactivation of the catalyst. Density functional theory studies indicate that the active species for the alkali-promoted systems is PtK6O4(OH)2 or a similar complex.

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