CHEMICAL-REACTIONS BETWEEN ATOMIC OXYGEN AND FORMIC-ACID ON PT(111)

We have studied the influence of 0.25 monolayer of atomic oxygen on th e interaction between formic acid and the (111) surface of Pt using th e techniques of thermal desorption spectroscopy and high resolution el ectron energy loss spectroscopy. At low coverages of formic acid the r eaction proceeds exclusively via unimolecular decomposition of a forma te intermediate, as it would also on the clean surface. Atomic oxygen reacts with the hydrogen released to form gaseous water; two distinct desorption states of water are assigned to reactions with the acid and acyl protons. At high coverages of formic acid there is evidence for new pathways other than unimolecular decomposition. These include reac tion between formate and hydroxyl to produce CO2 and H2O at temperatur es below 200 K and reaction between formate and water to produce dimer ic, gaseous HCOOH.