Water-gas shift activity on Pt-Re surfaces and the role of the support

The activity of Pt-Re surfaces was studied for the water-gas shift (WGS) reaction in order to understand how Pt-Re interactions and cluster-support interactions influence activity. The results from these studies were also compared with previous reports of WGS activity on Pt-Re clusters grown on TiO₂. Platinum on Re surfaces were prepared by annealing Re films on Pt(111) to form Pt-Re surface alloys, depositing Pt on Re/Pt(111), and depositing Pt on Re clusters supported on highly oriented pyrolytic graphite (HOPG) surfaces. In all cases, the turnover frequency (TOF) for the WGS reaction was higher for Pt with subsurface Re compared to pure Pt. Furthermore, the TOF for 2 ML Pt/TiO₂ clusters was greater than that of Pt(111) and 2 ML Pt/HOPG clusters, indicating that the TiO₂ support enhances activity for the WGS reaction on Pt. For Pt/TiO₂ clusters, a plot of the fraction of perimeter/surface sites as a function of Pt coverage closely follows TOF vs Pt coverage, strongly suggesting that activity occurs at the Pt-TiO₂ interface. Notably, the fraction of undercoordinated sites as a function of Pt coverage does not follow the same behavior as the TOFs.