Fourier-transform infrared studies of carbon monoxide adsorption on platinum sols in alcoholic media
The influence of a broad range of organic alcohols on CO adsorption on platinum hydrosols has been investigated by infrared spectroscopy. Aliphatic alcohols from ethanol to n-heptanol were found to inhibit CO adsorption on platinum hydrosol surfaces as demonstrated by the decrease in ν(CO)ads and CO coverage with increasing alcohol concentration. IR spectra of CO adsorbed on platinum extracted into long-chain alcohols revealed broad asymmetric ν(CO)ads bands at lower frequency indicating CO adsorption at reduced coverage on colloidal platinum. It is believed that the hydroxyl group in the C4–C8n-alcohols, essential for the extraction of colloidal platinum into these media is adsorbing via association with the oxide surface of the platinum sol particles. The addition of a poly(vinyl alcohol) protecting agent to the hydrosol led to significant reduction in ν(CO)ads and CO coverage suggesting inhibition of CO adsorption by the protecting agent. At pH < 4, the behaviour of CO adsorbed on the protected hydrosol appeared similar to that for CO adsorbed on a platinum electrode surface in acidic media.