A study of formaldehyde formation during methanol oxidation over PtRu bulk alloys and nanometer scale catalyst

Abstract

The oxidation of 1.0 M CH3OH in 0.1 M H2SO4 was carried out over PtRu bulk alloy and nanometer scale catalyst materials. The H2CO produced as a stable by-product during brief (180 s) electrolysis periods was determined quantitatively for potentials (measured vs a reversible hydrogen electrode reference) in the range of 0.5–0.8 V. Electrolysis was performed in a cell that accommodated a small (∼50 μL) sample volume. The experimental conditions kept the reactant depletion in the cell below 1%. Three arc melted bulk alloys were employed with respective Ru mole fractions (XRu) of 0.1, 0.3 and 0.9. The alloy surfaces were cleaned by bench top methods prior to measurements. For reaction potentials ⩾0.7 V, H2CO yields tended to become lower as the Ru content of the alloy electrode increased. However, at low (0.5 V) potentials the H2CO yields were at a minimum in reactions over the XRu = 0.3 bulk alloy. The oxidation of CH3OH over bulk polycrystalline Pt produced H2CO yields that were greater than those of the PtRu alloys, with the largest differences occurring for the XRu = 0.3 sample. For CH3OH oxidation over nanometer scale PtRu catalyst, the metal loadings (50–100 μg/cm2) were in a range known to be favorable for conversion of CH3OH to CO2 owing to a porous, multilayer structure formed by the particles on the support (Au) electrode which enables partial oxidation products to undergo multiple encounters with catalytic sites within the film. The nanometer scale catalyst materials studied (Pt and PtRu with XRu ≈ 0.1, 0.25 and 0.5) produced H2CO yields below 10% for all reaction potentials. Although the H2CO yields were low, trends similar to those of the bulk materials are apparent.