Reaction mechanism of WGS and PROX reactions catalyzed by Pt/oxide catalysts revealed by an FeO(111)/Pt(111) inverse model catalyst

We have employed XPS and TDS to study the adsorption and surface reactions of H2O, CO and HCOOH on an FeO(111)/Pt(111) inverse model catalyst. The FeO(111)-Pt(111) interface of the FeO(111)/Pt(111) inverse model catalyst exposes coordination-unsaturated Fe(II) cations (Fe(II)(CUS)) and the Fe(II)(CUS) cations are capable of modifying the reactivity of neighbouring Pt sites. Water facilely dissociates on the Fe(II)(CUS) cations at the FeO(111)-Pt(111) interface to form hydroxyls that react to form both water and H-2 upon heating. Hydroxyls on the Fe(II)(CUS) cations can react with CO(a) on the neighbouring Pt(111) sites to produce CO2 at low temperatures. Hydroxyls act as the co-catalyst in the CO oxidation by hydroxyls to CO2 (PROX reaction), while they act as one of the reactants in the CO oxidation by hydroxyls to CO2 and H-2 (WGS reaction), and the recombinative reaction of hydroxyls to produce H-2 is the rate-limiting step in the WGS reaction. A comparison of reaction behaviors between the interfacial CO(a) + OH reaction and the formate decomposition reaction suggest that formate is the likely surface intermediate of the CO(a) + OH reaction. These results provide some solid experimental evidence for the associative reaction mechanism of WGS and PROX reactions catalyzed by Pt/oxide catalysts.