New insights into the kinetics of formic acid decomposition on copper surfaces.

We use both time-resolved and static high resolution electron energy loss spectroscopies (EELS) to follow the chemisorption and subsequent decomposition of formic acid (HCOOH) on a Cu (100) surface. Two stable forms of chemisorbed formic acid have been identified: one existent at elevated temperatures is symmetrically bonded and oriented normal to the surface whereas the second, a low temperature high coverage structure, is canted. This tilting is not reversible at constant coverage, but can be driven by dosing the sample with formic acid while cooling. The implications of our results with respect to the catalytic dehydrogenation of formic acid on copper at high surface coverage are discussed.