EFFECT OF CO ON PT-CATALYZED DECOMPOSITION OF FORMIC-ACID IN ULTRAHIGH-VACUUM

Previous work has established that Pt(111) catalyzes the decomposition of formic acid via a formate intermediate, ultimately yielding CO2 and H-2 as gas-phase products in the environment of ultrahigh vacuum. In this work, we describe the effect of CO, which is a known poison in the electrochemical oxidation of formic acid at Pt surfaces. We find that CO exerts two main effects. First, it prevents conversion of molecular acid to the formate intermediate and promotes desorption of the molecular acid, both as monomers and oligomers. Presumably this is due to blocking of sites necessary to accommodate the dissociation products. Second, CO promotes a new but minor decomposition pathway by which up to 0.04 monolayers of the acid reacts. These results are compared with the electrochemical literature.