The surface species whose decomposition gives rise
to the high temperature peaks is a surface formate.
The surface species whose decomposition gives rise
to the high temperature peaks is a surface formate.
Rationale
The hydrogen evolved at low temperatures (approx. 50 % of the total desorbed hydrogen) presumably corresponds to the acidic hydrogen of the formic acid, indicating that the formic acid decomposes at low temperatures (possibly at the dosing temperature of 200 K and certainly below 250 K) to give the formate species and adsorbed atomic hydrogen.
| Recombination and desorption of this hydrogen (at ca. 280 K) H(ads) + H(ads) → H2 (g) leaves only the formate species on the surface. The formate species is stable to relatively high temperatures but eventually decomposes yielding the observed coincident desorption of hydrogen and carbon dioxide. |  |
The hydrogen trace thus contains examples of both a desorption limited peak (at ca. 280 K) and a decomposition limited peak (at ca. 440-470 K)
