Monitoring The Interaction Of Co With Graphene Supported Ir Clusters By Vibrational Spectroscopy And Density Functional Theory Calculations

The interaction of carbon monoxide (CO) with graphene supported Ir cluster (Ir/graphene/Ir(111)) and a Ir(111) single crystal surface was studied by infrared reflection- adsorption spectroscopy (IRRAS). The cluster morphology was characterized by scanning tunneling microscopy and density functional theory (DFT) calculations predicted the adsorption frequencies of CO molecules on the Ir single crystal surface and clusters. After exposing the clean Ir(111) surface to CO at 195 K, one intense vibrational band is observed at 2043 cm(-1), which is assigned to on top CO species. This band shifts to a much higher frequency at 2082 cm(-1) at higher CO exposure. After exposing clean graphene/Ir(111) to CO at 195 K, no CO band was observed in the IR spectra, which confirms a full graphene layer over the Ir(111) surface. However, CO molecules adsorb on Ir clusters supported on graphene/Ir(111) at 195 K. For the 0.05, 0.1, 0.15, and 0.2 ML Ir clusters, two IR bands were observed at 2060 and 2088 cm(-1), 2050 and 2070 2048 and 2070 cm(-1), and 2052 and 2070 cm(-1), respectively. The IR bands at lower frequencies are assigned to the CO on one-layer high clusters, and the IR bands at higher frequencies are assigned to the CO adsorption on two- or several-layer high clusters. The IR frequencies of CO adsorbed on clusters are shifted to lower wavenumbers compared to those observed on the single crystal surface, which is in agreement with DFT calculations. The IRRAS data recorded after CO adsorption on Ir clusters at different temperatures demonstrate that CO species are stable up to 350 K, although the intensity of CO on top one-layer high cluster reduces largely, indicating CO-induced cluster sintering.