The adsorption of CO, H-2, N2O, NH3 and CH4 gases on the anatase TiO2 (001) and (101) 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 (001) and (101) surfaces are in orders: NH3 (Delta E-ads = 26.6 kcal mol(-1)) >> CO (Delta E-ads = 9.7 kcal mol(-1)) >> H-2 approximate to CH4 approximate to N2O and NH3 (Delta E-ads = 24.3 kcal mol(-1)) >> CO (Delta E-ads = 6.8 kcal mol(-1)) approximate to N2O > CH4, respectively. The N2O energetically likes better to adsorb on the TiO2 (101) than the (001) surface. The H-2 dislike to adsorb on the TiO2 (101) but weakly adsorb on the TiO2 (001) surface. The CH4 weakly adsorbs on the TiO2 (001) surface but very weakly adsorbs on the TiO2 (101). Two configurations for co-adsorption of N2O and CO as [O=N=N center dot center dot center dot CO] and [CO center dot center dot center dot O=N=N] were found. (C) 2010 Elsevier B.V. All rights reserved.