Density Functional Theory based study of methanol adsorption and decomposition low index Miller CeO2 surfaces

M.M. BRANDA; A. BRUIX; F. ILLAS

Congreso; XXXIX Congreso Internacional de Químicos Teóricos de Expresión Latina (QUITEL),; 2013

XXXIX Congreso Internacional de Químicos Teóricos de Expresión Latina (QUITEL)

Adsorption and decomposition of methanol on different sites of the (111), (221), (331) and (110)low index Miller ceria surfaces has been studied by means of periodic density functional theory (DFT) calculations using the repeated slab model. These calculations have been carried out using the PW91 form of the Generalized Gradient Approximation (GGA) corrected with the so called on-site Hubbard parameter (U), a plane wave basis set to represent the valence density and the PAW description of the atomic cores. All calculations have been carried out with the Vienna  Ab-Initio Simulation Package (VASP). Initially, we have analyzed the methanol adsorption on all sites of the mentioned CeO2 surfaces.We found that the strongest interaction involves on top sites of the stepped (221) and (331) surfaces. However, it is also possible on the only (110) adsorption site and in the middle of the (331) step. The decomposition from methanol to methoxy and H were studied starting from the same sites except for the most internal site on (331) surface where methanol adsorption is very unlikely. For this react on the preferred initial configurations  correspond to top site for CeO2(221) and CeO2(110) surfaces. For these two surfaces, the activation energy (Eact) is smaller than 0.10 eV. The activation energy for the inverse reaction (E-act) for CeO2(110) surface was very large and similar to the results found for the dissociationof the water molecule on the same surface. The step ofthe CeO2(331) was found to exhibit a similar reactivity with Eact=+0.12eV and E-act=+0.51eV. To summarize, the methanol adsorption can take place on all studied surfaces with energies between ~ -0.5 eV and ~0.7 eV, then the dissociation reaction is more probable on the stepped CeO2(221) and CeO2(331) surfaces and also on the CeO2(110) surface. In addition, the methanol decomposition to formaldehyde species on CeO2(111) surface seems to have an important energetic cost and it should occur on more reactive surfaces. Work is in progress to complete the energy profile from methanol to formaldehyde on the rest of studied ceria surfaces.