The Oxidisation of Methanol Catalysed by Gold, Palladium and Gold-Palladium Alloys

The results of an investigation of the catalytic oxidation of methanol over a series of gold, palladium and alloy catalysts are reported.
The work was carried out in flow system at atmospheric pressure using nitrogen as a diluent. The catalyst was an electrically heated wire, whose temperature was found by determining its resistance and comparing the result with a previous experimental calibration.
Reaction products were estimated by gas-liquid chromatography, infra-red spectrophotometry and visible absorptiometry. The products detected over gold were formaldehyde, hydrogen and water. As palladium was progressively introduced into the catalyst the amount of carbon oxides detected increased. This was ascribed to the further oxidation of methanol or formaldehyde, with subsequent desorption of carbon monoxide via surface gold sites.
The apparent energy of. activation fell from 121 kg mol-1 over gold to a value of 40 to 50 kJ mo1-1 over gold rich alloys. This was correlated with the work of Stephens who showed that the introduction of a small amount of palladium into a gold surface increased the surface concentration of oxygen by migration of oxygen from palladium sites.
The alloy containing 40 atom percent palladium was found to be almost inactive for the catalytic oxidation of methanol. It is known that this composition is particularly susceptible to short range order. It is suggested that this led to a decrease in the availability of electrons for donation to the chemisorbing oxygen and hence to a very low oxygen surface population.
Arrhenius plots obtained for three palladium rich catalysts exhibited a change of slope, which was also noted by Firth. This work and other literature results suggest that palladium operates in three different modes, depending on the oxidation state of the surface.