In situ reflection-absorption infrared spectroscopy at the liquid-solid interface:: decomposition of organic molecules on polycrystalline platinum substrates

The room-temperature adsorption and surface chemistry of several categories of organic molecules used as reactants or solvents in liquid-phase catalysis, of carboxylic acids, esters, aldehydes, acetone, alcohols and ethers in particular, were characterized in situ on polycrystalline Pt in the presence of the liquid phase by reflection-absorption infrared spectroscopy (RAIRS). For carboxylic acids and esters it was found that the propensity for decomposition and CO formation follows a formic acid >> methyl formate, ethyl formate > acetic acid, propionic acid, acrylic acid, ethyl acetate sequence. For aldehydes and acetone, the observed trend is formaldehyde >> acetaldehyde > acrolein, crotonaldehyde > propionaldehyde, acetone. Virtually no adsorbed CO was detected when Pt surfaces were exposed to liquid solutions of either alcohols or ethers. The observed trends could be correlated with the corresponding molecular structures. They are discussed in the context of previous results obtained from studies under ultrahigh vacuum (UHV) and under electro-oxidation conditions.