Adsorption of CO, H2, N2O, NH3 and CH4 on the anatase TiO2 (0 0 1) and (1 0 1) surfaces and their competitive adsorption predicted by periodic DFT calculations

The adsorption of CO, H2, N2O, NH3 and CH4 gases on the anatase TiO2 (0 0 1) and (1 0 1) surfaces was investigated by two-dimensionally periodic slab model DFT calculation. The most energetically favorable positions of these gases on the anatase TiO2 surface computed using two different optimization models were obtained. The relative adsorption energies of these gases on the anatase TiO2 (0 0 1) and (1 0 1) surfaces are in orders: NH3 (ΔEads = −26.6 kcal mol−1) ≫ CO (ΔEads = −9.7 kcal mol−1) ≫ H2 ≈ CH4 ≈ N2O and NH3 (ΔEads = −24.3 kcal mol−1) ≫ CO (ΔEads = −6.8 kcal mol−1) ≈ N2O > CH4, respectively. The N2O energetically likes better to adsorb on the TiO2 (1 0 1) than the (0 0 1) surface. The H2 dislike to adsorb on the TiO2 (1 0 1) but weakly adsorb on the TiO2 (0 0 1) surface. The CH4 weakly adsorbs on the TiO2 (0 0 1) surface but very weakly adsorbs on the TiO2 (1 0 1). Two configurations for co-adsorption of N2O and CO as [Odouble bond; length as m-dashNdouble bond; length as m-dashN⋯CO] and [CO⋯Odouble bond; length as m-dashNdouble bond; length as m-dashN] were found.