Theoretical Study on the Decomposition of HCOOH on a ZnO(10[formula omitted]0) Surface

Abstract

The mechanism of the decomposition of formic acid HCOOH on ZnO(1010) surfaces was investigated using theab initiomolecular orbital method. Furthermore, the role of the dynamic bending of the surface formate anion HCOO−in the decomposition reaction was also examined. The lattice Zn atom interacts with the C–H bond of the adsorbed formate anion and cleaves the C–H bond to yield adsorbed CO2and ZnH species. However, similar results are not obtained with the lattice O atom or surface OH species. The energy barriers of C–H bond cleavage and CO2desorption from the surface were calculated to be 45.5 and 11.2 kcal/mol, respectively, at the MP2 level. H2formation is a bimolecular process: another formic acid from the gas phase attacks the ZnH surface species and produces an H2molecule. The calculated energy barrier is 2.2 kcal/mol and the exothermicity of the reaction is 11.3 kcal/mol at the MP2 level. These results indicate that the rate-determining step of the dehydrogenation decomposition of formic acid is cleavage of the C–H bond. Both the decomposition reaction and the dissociative adsorption of HCOOH occur more easily on hydrogen-covered surface than on a clean surface.