A DFT study of formic acid decomposition on the stoichiometric SnO2 surface as a function of iso-valent doping

• Iso-valent dopants introduced in the SnO 2 lattice and replacing a Sn ion prefer to be in surface or sub-surface layers, and not in the bulk. • The presence of iso-valent dopants does not alter the electronic structure by introducing excess electrons or holes in the system but rather they slightly modify the local geometrical structure of the surface or they introduce empty states in the gap of SnO 2 . • Formic acid adsorbs in a bidentate mode on the SnO 2 surface; the bonding is only moderately affected by the presence of the dopants. • Formic acid decomposition can follow four paths releasing: (a) H 2 (g) + adsorbed CO 2 , (b) H 2 O(g) + adsorbed CO, (c) CO(g) + adsorbed H 2 O, or (d) CO 2 (g) + adsorbed H 2 . • Some of the decomposition paths, CO 2 release and H 2 adsorption in particular, can be affected by the presence of dopants on the surface. In the present work, we have studied the effect of iso-valent dopants on the chemical reactivity of the stoichiometric SnO 2 (110) surface. Si, Ge, Pb, Ti, Zr, Hf, and Ce ions have been placed at the Sn lattice sites (substitutional doping) in bulk, sub-surface, and surface positions. The results show that surface or sub-surface sites are clearly preferred over the bulk ones. Next, we studied the effect of the iso-valent dopants on the adsorption and decomposition reaction of HCOOH molecule. On this basis, four paths with desorption of: (a) H 2, (b) CO, (c) H 2 O, or (d) CO 2 can occur. Comparing the results of this decomposition reaction on the SnO 2 surface with the same process on rutile TiO 2 (110) having the same structure and morphology, reveals that SnO 2 is considerably more reactive in all reaction steps of the formic acid decomposition.