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 (H(2)O + CO → H(2) + CO(2)) used for producing H(2). 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-O(x)(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.

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Applying density functional theory (DFT) calculations to the rational design of catalysts for complex reaction networks has been an ongoing challenge, primarily because of the high computational cost of these calculations. Certain correlations can be used to reduce the number and complexity of DFT calculations necessary to describe trends in activity and selectivity across metal and alloy surfaces, thus extending the reach of DFT to more complex systems. In this work, the well-known family of Brønsted-Evans-Polanyi (BEP) correlations, connecting minima with maxima in the potential energy surface of elementary steps, in tandem with a scaling relation, connecting binding energies of complex adsorbates with those of simpler ones (e.g., C, O), is used to develop a potential-energy surface for ethanol decomposition on 10 transition metal surfaces. Using a simple kinetic model, the selectivity and activity on a subset of these surfaces are calculated. Experiments on supported catalysts verify that this simple model is reasonably accurate in describing reactivity trends across metals, suggesting that the combination of BEP and scaling relations may substantially reduce the cost of DFT calculations required for identifying reactivity descriptors of more complex reactions.

We have investigated the structure sensitivity of methanol electrooxidation on eight transition metals (Au, Ag, Cu, Pt, Pd, Ir, Rh, and Ni) using periodic, self-consistent density functional theory (DFT-GGA). Using the adsorption energies of 16 intermediates on two different facets of these eight face-centered-cubic transition metals, combined with a simple electrochemical model, we address the differences in the reaction mechanism between the (111) and (100) facets of these metals. We investigate two separate mechanisms for methanol electrooxidation: one going through a CO* intermediate (the indirect pathway) and another that oxidizes methanol directly to CO(2) without CO* as an intermediate (the direct pathway). A comparison of our results for the (111) and (100) surfaces explains the origin of methanol electrooxidation's experimentally-established structure sensitivity on Pt surfaces. For most metals studied, on both the (111) and (100) facets, we predict that the indirect mechanism has a higher onset potential than the direct mechanism. Ni(111), Au(100), and Au(111) are the cases where the direct and indirect mechanisms have the same onset potential. For the direct mechanism, Rh, Ir, and Ni show a lower onset potential on the (111) facet, whereas Pt, Cu, Ag, and Au possess lower onset potential on the (100) facet. Pd(100) and Pd(111) have the same onset potential for the direct mechanism. These results can be rationalized by the stronger binding energy of adsorbates on the (100) facet versus the (111) facet. Using linear scaling relations, we establish reactivity descriptors for the (100) surface similar to those recently developed for the (111) surface; the free energies of adsorbed CO* and OH* can describe methanol electrooxidation trends on various metal surfaces reasonably well.