The reaction of CO and O 2 with submonolayer and multilayer CoO x films on Pt(111), to produce CO 2 , was investigated at room temperature in the mTorr pressure regime. Using operan do ambient pressure X-ray photoelectron spectroscopy and high pressure scanning tunneling microscopy, as well as density functional theory calculations, we found that the presence of oxygen vacancies in partially oxidized CoO x films significantly enhances the activity of CO oxidation to form CO 2 upon exposure to mTorr pressures of CO at room temperature. In contrast, CoO films without O-vacancies are much less active for CO 2 formation at RT, and CO only adsorbed in the form of carbonate species stable up to 260° C. On submonolayer CoO x islands, the carbonates form preferentially at island edges, deactivating the edge sites for CO 2 formation, even while the reaction proceeds inside the islands. These results provide a detailed understanding of CO oxidation pathways on systems where noble metals such as Pt interact with reducible oxides. ASSOCIATED CONTENTSupporting Information. XPS peak fitting procedures, further temperature dependent XPS measurements, XPS of multilayer films in CO and CO + O 2 mixtures, irreducibility of carbonate films, further discussion of CoO x films, and additional DFT calculation details and results. This material is available free of charge via the internet at http://pubs.acs.org.

With appropriate choice of ligands, Mn 3 -based single-molecule magnets (SMMs) can be covalently linked to form SMM dimers that exhibit either ferromagnetic (FM) or antiferromagnetic (AFM) ground state. We present here results of density functional theory (DFT)-based calculations that elucidate the effect of two different types of support, graphene and two-dimensional hexagonal boron nitride (h-BN), on the electronic structure and magnetic properties of the ligated Mn 3 dimers. Our calculations for the spin per Mn 3 monomer of both the FM and AFM configurations of the isolated Mn 3 dimers in the gas phase agree with experimental results (S = 6) when the dimers are explicitly charged to a +2 state, the charged state found in experimental observations. Following the determination of the most stable configuration of each dimer on graphene and h-BN, the analysis of their spin reveals that their magnetic properties are not noticeably affected when adsorbed on these two-dimensional materials. The charge density, charge transfer, and binding analysis reveals that the dimers are physisorbed on both graphene and h-BN through van der Waals interactions, with charge transfer taking place in the case of graphene only. Our results provide insights into the design of proposed experiments for measuring transport properties of these AFM and FM dimers and the critical role played by graphene and h-BN as supports.

Noble metal nanoclusters (NCs) play a pivotal role in bridging the gap between molecules and quantum dots. Fundamental understanding of the evolution of the structural, optical, and electronic properties of these materials in various environments is of paramount importance for many applications. Using state-of-the-art spectroscopy, we provide the first decisive experimental evidence that the structural, electronic, and optical properties of Ag(MNBA) NCs can now be tailored by controlling the chemical environment. Infrared and photoelectron spectroscopies clearly indicate that there is a dimerization between two adjacent ligands capping the NCs that takes place upon lowering the pH from 13 to 7.

It is well-known experimentally that at ½ monolayer (ML) coverage CO forms a c(4×2) phase on Pd(111). There is, however, a debate about whether this adsorption is at the bridge or at the hollow (FCC and HCP) sites, or at a combination of these two types of sites. Using density functional theory based calculations to evaluate the structural and vibrational properties of the c(4×2) overlayer structure of CO on Pd(111), with all possible highly symmetric adsorption sites, we conclude that the CO molecules prefer to adsorb either only on the hollow (FCC or HCP) sites or only at sites which are located in-between the bridge and the FCC sites and that there is no stable overlayer structure in which the molecule binds only at the bridge sites or combination of bridge and hollow sites.

We find that exposure of the MoS2 basal plane to methanol leads to the formation of adsorbed methoxy and coincides with sulfur vacancy generation. The conversion of methanol to methoxy on MoS2 is temperature dependent. Density functional theory simulations and experiment indicate that the methoxy moieties are bound to molybdenum, not sulfur, while some adsorbed methanol is readily desorbed near or slightly above room temperature. Our calculations also suggest that the dissociation of methanol via O–H bond scission occurs at the defect site (sulfur vacancy), followed subsequently by formation of a weakly bound H2S species that promptly desorbs from the surface with creation of new sulfur vacancy. Photoluminescence and scanning tunneling microscopy show clear evidence of the sulfur vacancy creation on the MoS2 surface, after exposure to methanol.