Oxidation of Methanol on 2nd and 3rd Row Group VIII Transition Metals (Pt, Ir, Os, Pd, Rh, and Ru):  Application to Direct Methanol Fuel Cells

Abstract

Using first principles quantum mechanics [nonlocal density functional theory (B3LYP)], we calculated the 13 most likely intermediate species for methanol oxidation on clusters of all 2nd and 3rd row Group VIII transition metals for all three likely binding sites (top, bridge, and cap). This comprehensive set of binding energies and structures allows a detailed analysis of possible reaction mechanisms and how they change for different metals. This illustrates the role in which modern quantum chemical methods can be used to provide data for combinatorial strategies for discovering and designing new catalysts. We find that methanol dehydrogenation is most facile on Pt, with the hydrogens preferentially stripped off the carbon end. However, water dehydrogenation is most facile on Ru. These results support the bifunctional mechanism for methanol oxidation on Pt−Ru alloys in direct methanol fuel cells (DMFCs). We find that pure Os is capable of performing both functionalities without cocatalyst. We suggest that pure Os be examined as a potential catalyst for low overpotential, highly dispersed catalyst DMFCs. Pathways to form the second C−O bond differ between the pure metals (Pt and Os) in which (CO)ads is probably activated by (OH)ads and the Pt−Ru binary system in which (COH)ads is probably activated by Oads. For all cases we find that formation of (COOH)ads is an important precursor to the final dehydrogenation to desorb CO2 from the surface.

Rapid Microwave Synthesis of CO Tolerant Reduced Graphene Oxide-Supported Platinum Electrocatalysts for Oxidation of Methanol

“…The presence of residual oxygen groups on the graphene support can promote the oxidation of CO adsorbed, CO ads , on the active Pt sites via the bifunctional mechanism. [10][11][12]16 The proposed mechanism is described in the following equations and denoted as 1 in the schematic of Figure 5b: Dissociative adsorption of water molecules on the RGO support creates RGO-(OH) ads surface groups adjacent to Pt NPs (eq 1), which readily oxidize CO ads groups on the peripheral Pt atoms (eq 2). The hydrophilic nature of RGO promotes water activation and is the major driver in this mechanism.…”

Pt-Ru-Ir Nanoparticles Prepared by Vapor Deposition as a Very Efficient Anode Catalyst for Methanol Fuel Cells

“…8 The above approach is implemented in the present work to prepare Pt-Ru-Ir nanoparticles on carbon powder substrate. Iridium has been selected as a third metal to be incorporated into Pt-Ru-based catalysts because it had been reported to be somewhat active ͑much less than Pt, though͒ for dissociative chemisorption of methanol 9,10 and, at the same time, to be able ͑similarly to Ru͒ to form surface bonded-OH groups which promote CO oxidation.…”

Ruthenium–Platinum Catalysts and Direct Methanol Fuel Cells (DMFC): A Review of Theoretical and Experimental Breakthroughs

“…Kua and Goddard define three stages to be considered in their computational research of the oxidation of methanol, stage one, of methanol dehydrogenation, stage two, of water dehydrogenation, and stage three, of second C-O bond formation [59]. Their data indicated that the most favorable pathway is via reaction of surface adsorbed COH and oxygen, terminating with the dehydrogenation of adsorbed COOH and consequent surface desorption of carbon dioxide.…”