Cu(111)-supported W3Ox clusters: Stoichiometry and symmetry effects on CO2 activation and dissociation

Density functional calculations with dispersion corrections (DFT-D) have been performed to study the adsorption and dissociation of CO₂ on W₃O_x/Cu(111) inverse catalyst (x = 9 or 6). The W₃O₉ aggregate adsorbs in several different geometries through the formation of O-Cu bonds, in all the cases taking electronic charge from the metal surface. The reduced W₃O₆ particle anchors very strongly to Cu by means of W-Cu bonds; in this case, the charge transfer is opposite than for W₃O₉/Cu yielding the oxide particle positively charged. CO₂ is activated on W₃O₆/Cu(111) at the oxide/metal interface; its dissociation was found to be exothermic and kinetically more favorable than on the pure counterparts, Cu(111) and WO₃(001) surfaces. In contrast, CO₂ is activated on W₃O₉/Cu(111) only in the form that is by far the least stable (the one possessing C_s symmetry). Our results suggest that stoichiometry and symmetry of Cu-supported W₃O_x clusters play a crucial role in CO₂ activation and dissociation. In particular, the mixed W₃O₆/Cu(111) system appears as a catalyst of great potential for reactions involving CO₂ dissociation.