The infrared spectra and stability of CO and H2O sorption over Ag-exchanged ZSM-5 zeolite were investigated by using density function theory (DFT). The changes of NBO charge show that the electron transfers from CO molecule to the Ag+ cation to form an sigma-bond, and it accompanies by the back donation of d-electrons from Ag+ cation to the CO (pi*) orbital as one and two CO molecules are adsorbed on Ag-ZSM-5. The free energy changes Delta G, -5.55 kcal/mol and 6.52 kcal/mol for one and two CO molecules, illustrate that the Ag+(CO)(2) complex is unstable at the room temperature. The vibration frequency of C-O stretching of one CO molecule bonded to Ag+ ion at 2211 cm(-1) is in good agreement with the experimental results. The calculated C-O symmetric and antisymmetric stretching frequencies in the Ag+(CO)(2) complex shift to 2231 cm(-1) and 2205 cm(-1) when the second CO molecule is adsorbed. The calculated C-O stretching frequency in CO-Ag-ZSM-5-H2O complex shifts to 2199 cm(-1), the symmetric and antisymmetric O-H stretching frequencies are 3390 cm(-1) and 3869 cm(-1), respectively. The Gibbs free energy change (Delta GH(2)O) is -6.58 kcal/mol as a H2O molecule is adsorbed on CO-Ag-ZSM-5 complex at 298 K. The results show that CO-Ag-ZSM-5-H2O complex is more stable at room temperature. (C) 2009 Elsevier B.V. All rights reserved.