Fourier-transform infrared studies of carbon monoxide adsorption on platinum sols in alcoholic media

Abstract

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.