We have systematically studied the CO oxidation on various nanosized gold clusters with sizes ranging from 0.3 to 0.8 nm on the basis of density functional theory (DFT) calculations. A hitherto unreported trimolecular Langmuir-Hinshelwood (LH) mechanism is proposed, which offers new insights into the fundamental mechanism for CO oxidation on nanosized gold clusters. Specifically, we find that the coadsorbed CO molecule at a unique triangular Au(3) active site can act as a promoter for the scission of an O-O bond, leading to the spontaneous formation (due to extremely low energy barrier) of two CO(2) molecules as product. The key step to the O-O bond scission in the OCOO* intermediate is significantly accelerated due to the electrophilic attack of the coadsorbed neighboring CO molecule on the triangular Au(3) site. This new mechanism is called CO self-promoting oxidation, which can be visualized in real time from the trajectory of a Born-Oppenheimer molecular dynamics (BOMD) simulation. We also find that such CO self-promoting oxidation is quite universal, as long as the triangular Au(3) reaction site is available. This is demonstrated in two prototype metal oxide supported gold nanostructure systems: namely, Au(n)/MgO and bilayer-Au/TiO(2). The coadsorbed CO can not only serve as a promoter for its own oxidation but also promote other oxidation reactions such as styrene oxidation through expediting O-O scission on gold nanostructures.
Figure S1. The snapshots of intermediates, transition states and products of different H-abstraction and OH-abstraction pathways displayed in Figure 1-5 in context.
The electronic and magnetic properties of transition metal (TM = Sc, Ti, V, Cr and Mn) atom incorporated single and double one-dimensional (1D) styrene molecular wires confined on the hydrogen-terminated Si(100) surface are explored for the first time by means of spin-polarized density functional theory, denoted as Si-[TM(styrene)]. It is unveiled that TM atoms bind asymmetrically to the adjacent phenyl rings, which leads to novel electronic and magnetic properties in stark contrast to the well-studied gas phase TM-benzene molecular wires. Si-[Mn(styrene)]∞ and Si-[Cr(styrene)]∞ single molecular wires (SMWs) are a ferromagnetic semiconductor and half metal, respectively. Creation of H-atom defects on the silicon surface can introduce an impurity metallic band, which leads to novel half-metallic magnetism of a Si-[Mn(styrene)]∞ system. Moreover, double molecular wires (DMWs) containing two identical or hetero SMWs are theoretically designed. The [Mn(styrene)]∞-[Cr(styrene)]∞ DMW exhibits half-metallic magnetism where the spin-up and spin-down channels are contributed by two single molecular wires. Finally, we demonstrate that introducing a TM-defect may significantly affect the electronic structure and magnetic properties of molecular wires. These studies provide new insights into the structure and properties of surface supported 1-D sandwiched molecular wires and may inspire the future experimental synthesis of substrate confined organometallic sandwiched molecular wires.
Gas-phase one-dimensional organometallic sandwich nanowires (SWNs) made by transition metal atoms and π-conjugated hydrocarbon rings have been subjected to intensive experimental and theoretical studies. In this work, we theoretically predicted the structures and studied the electronic and magnetic properties of a new type of surface confined 3d transition metal (TM = Sc, Ti, V, Cr, and Mn) decorated vinylnaphthalene molecular wires anchored on the hydrogenterminated Si(100)-(2 × 1) surface, denoted as Si-[Vinylnaphthalene-TM 2 ] ∞ . On basis of the spin-polarized density functional theory (DFT) calculations, we find these surface confined SWNs possess novel electronic and magnetic properties in contrast with their gas-phase analogues. Because of one end of the naphthalene rings is fixed on the silicon surface through a vinyl group, the TM atoms cannot efficiently coordinate to the naphthalene rings. Even though, the Si-[vinylnaphthalene-TM 2 ] ∞ SWNs still show large binding energies for metal atoms. The electronic structure calculations demonstrate that the Si-[vinylnaphthalene-TM 2 ] ∞ SWNs can be ferromagnetism (TM = Cr and Mn), nonmagnetism (TM = Sc and V), or antiferromagnetism (TM = Ti). The half metallic property is found for the Mn-decorated SWNs.
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