MBRS Measurements of Overlayer Effects on Surface Lifetimes and Reaction Probabilities

The interaction of formic acid with Ni( 1 lo), Ni( 1 lO)-carbide, Ni( 1 IO)-graphite, and Ni( 1 lO)sulfide surfaces was examined by molecular beam relaxation spectrometry. The apparent firstorder rate constants for the desorption of formic acid (T, < 300°K) were remarkably similar on all of the surfaces studied, suggesting that the low-temperature formic acid adsorption/desorption interactions were essentially identical on the different catalytic surfaces investigated. The onset of formic acid decomposition occurred in the vicinity of room temperature for the different surfaces examined, and the decomposition probabilities above room temperature varied appreciably from surface to surface. The decomposition probabilities above room temperature were 0.9 for Ni( 1 lo), 0.5 for Ni( I lO)-carbide, and ~0.1 for Ni( 1 IO)-graphite and Ni(1 IO)-sulfide.