Anand Udaykumar Nilekar

Alkali-Stabilized Pt-OHx Species Catalyze Low-Temperature Water-Gas Shift Reactions

Substituting Salt for Cerium Oxide The water-gas shift reaction converts carbon monoxide and water to hydrogen and carbon dioxide. Catalysts that operate at lower temperatures will be useful in fuel cells. Nanoparticles of platinum adsorbed on reducible oxides, such as ceria, can stabilize catalytically active Ptoxygen species. Zhai et al. (p. 1633) now show that, when alkali atoms are added, atomically dispersed Pt can be an active catalyst for the water-gas shift reaction at ∼100°C, even on simple oxides such as alumina and silica. The formation of hydrogen from carbon monoxide and water is catalyzed by the formation of oxidized platinum atoms. We report that alkali ions (sodium or potassium) added in small amounts activate platinum adsorbed on alumina or silica for the low-temperature water-gas shift (WGS) reaction (H2O + CO → H2 + CO2) used for producing H2. The alkali ion–associated surface OH groups are activated by CO at low temperatures (~100°C) in the presence of atomically dispersed platinum. Both experimental evidence and density functional theory calculations suggest that a partially oxidized Pt-alkali-Ox(OH)y species is the active site for the low-temperature Pt-catalyzed WGS reaction. These findings are useful for the design of highly active and stable WGS catalysts that contain only trace amounts of a precious metal without the need for a reducible oxide support such as ceria.

Mixed-Metal Pt Monolayer Electrocatalysts with Improved CO Tolerance

Using a combination of periodic, self-consistent, density functional theory (DFT) calculations and CO-stripping voltammetry experiments, we have designed a new class of Pt-M bimetallic monolayer catalysts supported on a non-Pt metal, which exhibit improved stability against CO poisoning and might be suitable for proton-exchange membrane fuel cell anodes. These surfaces help in reducing the overpotential associated with anodic CO oxidation and minimize the amount of Pt used, thereby reducing materials cost. DFT calculations predict highly repulsive interactions between adsorbed CO molecules on these surfaces, leading to weaker binding and lower coverage of CO than on pure Pt, which in turn facilitates oxidative removal of CO from these catalytic surfaces.

Manipulation and Patterning of the Surface Hydrogen Concentration on Pd(111) by Electric Fields

Manipulation and patterning of the surface hydrogen concentration on Pd(111) by electric fields T. Mitsui, E. Fomin, D.F. Ogletree and M. Salmeron Lawrence Berkeley National Laboratory. Berkeley, CA 94720. USA A. U. Nilekar and M. Mavrikakis Department of Chemical & Biological Engineering University of Wisconsin-Madison, Madison, WI 53706. USA [**] Work at LBL was supported by the Director, Office of Energy Research, Office of Basic Energy Sciences, Materials Sciences Division of the U.S. Department of Energy under contract No. DE-AC02-05CH11231. Work at UW was supported by DOE-BES, Division of Chemical Sciences, under contract No. DE-FG02-05ER15731. AUN and MM thank SC Johnson & Son, Inc. for a Distinguished Fellowship. Computational resources at DOE-NERSC, PNNL, and ORNL are gratefully acknowledged.