The adsorption and decomposition of formaldehyde and formic acid on the clean and modified Fe (100) surface

Abstract

The adsorption and thermal reaction of formaldehyde and formic acid on the clean and modified Fe(100) surface is studied. CH 2O adsorbs molecularly on the clean Fe(100) surface without the formation of polymer (CH 2O) x (paraformaldehyde) at exposures below 3.0 L. At 223 K, molecularly adsorbed CH 2O is hydrogenated to form methoxy and dehydrogenated to form surface CO. Coadsorption of H 2O and hydroxy species can oxidize this methoxy species to form formate. Methanol is observed as one of the desorption products for the coadsorption of H 2O or OH and CH 2O. The presence of adatomic C induces the formation of (CH 2O) x polymers on the surface and changes the mechanism of CH 2O decomposition. The presence of adatomic O decreases CH 2O decomposition and increases molecular CH 2O desorption. Oxygen alters the reactivity of the surface but not the reaction pathway for CH 2O decomposition. At low exposures, formic acid adsorbs to produce a bidentate formate species on the Fe(100) surface at 100 K. A monodentate formate is observed at high coverage, which converts into a bidentate formate with higher symmetry at 253 K. This surface formale further decomposes to either desorb CO or form O (ad) and C (ad). On the c(2×2)-O and p(1×2)-OH surfaces, formic acid transfers carboxylic hydrogen to preadsorbed oxygen or hydroxyl to desorb H 2O during the thermal decomposition reaction.