First principles study of CO adsorption–CO 2 desorption mechanisms on oxidized doped‐gold cationic clusters MAu n O m + (M = Ti, Fe; n = 1,4–7; m = 1–2)

A first principles study of the formation and desorption of CO 2 on oxidized doped‐gold complexes MAu n O   m +is presented for n = 1,4–7, m = 1–2, and M = Ti, Fe. We start with the ground state geometry of MAu n O   2 +complexes obtained in a previous work. After the adsorption of a first CO molecule on MAu n O   2 + , two intermediate complexes with small energy difference are preferably formed, one of them with a preformed CO 3 carbonate and the other one with a preformed CO 2 . The former is more bound than the later only for n = 6–7, and for FeAu 4 O   2 + . Two mechanism for the desorption of CO 2 are studied. In the first one, here called sequential mechanism, we choose the intermediate O‐MAu   n + ‐CO 2 complex with a preformed CO 2 as the preferential to desorb a CO 2 molecule leaving the MAu n O + cluster. A second CO molecule is then adsorbed on that residual aggregate forming, among other equilibrium compositions, a MAu   n + ‐CO 2 complex from which a CO 2 molecule can be desorbed to yield the deoxidized MAu   n +bimetallic cluster. In the second CO 2 desorption mechanism, called here simultaneous mechanism, we consider the adsorption of a second CO on each one of MAu   n + ‐CO 3 and O‐MAu   n + ‐CO 2 intermediate complexes resulting from the first CO adsorption. Three types of new intermediate complexes are preferably formed: (a) MAu   n + ‐CO‐CO 3 with preformed CO 3 and CO radicals; (b) MAu   n + ‐C 2 O 4 with a preformed C 2 O 4 oxalate; (c) MAu   n + ‐CO 2 ‐CO 2 with two preformed CO 2 molecules bonded on the M impurity. We calculate the simultaneous desorption of two CO 2 molecules from the intermediate complex of case (c) leaving the deoxidized MAu   n +cluster in the ground state, except for a few cases where FeAu   n +structural deformation occurs following the optimization of intermediate complexes. The effects of cluster size and transition metal impurity on the CO adsorption and CO 2 desorption energies are discussed. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011