Acetic acid adsorption and decomposition on Pd(1 1 0)

The reaction of acetic acid with Pd(1 1 0) has been investigated using temperature-programmed desorption (TPD) and a molecular beam reactor. The sticking of acetic acid is very efficient and results in hydrogen evolution and acetate formation at room temperature. The acetate decomposes between 320 and 440 K to produce CO2 and hydrogen coincidently and leaves C adsorbed on the surface. The presence of carbon results in a changed desorption profile after readsorbing acid on the surface, manifesting an autocatalytic decomposition profile, with a half-height width of as low as 9 K and a slowed decomposition rate (higher peak temperature). Surprisingly, at higher temperatures where the acetate is unstable (>450 K), the sticking of acetic acid continues at a steady-state rate and is not poisoned by the build-up of C on the crystal. This is due to the fact that most of the C deposited is lost from the surface to the bulk in a facile manner above about 450 K, leaving a reactive surface which is apparently continually available for decomposition. The reactive surface appears to be Pd(1 1 0) with 0.5 monolayers of C adsorbed in the c(2 × 2) structure, which acts as a template for increased stability and ordering of the acetate adlayer.