Mechanism for the Water-Gas Shift Reaction On Pt(111) and Catalyst Deactivation

The behavior of monofunctional platinum, Pt(111), for the water-gas shift reaction has been investigated using experimental and theoretical methods.  Kinetic and isotopic measurements performed from 525 – 675 K are consistent with an associative mechanism for the water-gas shift reaction.  The sole kinetically relevant step consists of the unimolecular decomposition of an adsorbed carboxylate intermediate. The turnover frequency of Pt(111) is five-times greater than that observed on Cu(111) under identical conditions (612 K, 26 Torr CO, 10 Torr H₂O); however, Pt(111) loses activity over time due to the formation of carbonaceous deposits, a process not observed in similar studies of Cu(111).  Our experimental and theoretical results suggest that CO dissociates via two pathways, the Boudouard reaction and through a COH intermediate.  Nucleation of carbon at step-edges and subsequent oligomerization deactivates the catalyst.  These results provide insight to the synergistic roles of noble metal clusters and supports for the water-gas shift reaction.