Adsorption of Transition-Metal Clusters on Graphene and N-Doped Graphene: A DFT Study

Using the dispersion-corrected density functional theory (DFT-D3) method, we systematically studied the adsorption of 15 kinds of transition-metal (TM) clusters on pristine graphene (Gr) and N-doped graphene (N-Gr). It has been found that TM_n (n = 1-4) clusters adsorbed on the N-Gr surface are much stronger than those on the pristine Gr surface, while 3d series clusters present similar geometries on Gr and N-Gr surfaces. The most preferred sites of TMs migrate from hollow to bridge to the top site on the Gr surface along the d series in the periodic table, while the preferred sites of TMs migrate in a much more complex manner on the N-Gr surface. It has also been found that charge transfer decreases along the d series for adsorbed clusters on both surfaces, but adsorbed clusters present less charge transfer on the N-Gr surface than on the Gr surface. What is more interesting is that some TM (Tc, Ru, and Re) clusters change the growth mechanism from the three-dimensional (3D) growth mode on the Gr surface to the two-dimensional (2D) growth mode on the N-Gr surface. At last, it has been found that adsorbed clusters are more dispersed on the N-Gr surface than on the pristine Gr surface due to growth and average aggregation energies.

A minireview on the synthesis of single atom catalysts

Single atom catalysis is a prosperous and rapidly growing research field, owing to the remarkable advantages of single atom catalysts (SACs), such as maximized atom utilization efficiency, tailorable catalytic activities as well as supremely high catalytic selectivity. Synthesis approaches play crucial roles in determining the properties and performance of SACs. Over the past few years, versatile methods have been adopted to synthesize SACs. Herein, we give a thorough and up-to-date review on the progress of approaches for the synthesis of SACs, outline the general principles and list the advantages and disadvantages of each synthesis approach, with the aim to give the readers a clear picture and inspire more studies to exploit novel approaches to synthesize SACs effectively.

Gold nanostructures on iron oxide surfaces and their interaction with CO

We review results of density functional theory calculations of the adsorption of single gold atoms and formation of sub-nanometer Aunstructures (n= 2 to 5) on most stable iron oxide surfaces: hematite (0001), and magnetite (111) and (001). Structural, energetic, and electronic properties of Aunstructures on both Fe- and O-rich oxide terminations are discussed. Different chemical character of the two oxide terminations is reflected in distinctly stronger binding of gold at the oxygen- than at the iron-terminated surface, and in different changes of the adsorption binding energy with the size of the Auncluster. On the iron-terminated oxide surface the binding energy increases whereas on the oxygen-rich termination it decreases with the number of Au atoms in the structure. Upon CO adsorption on magnetite surface all Aunstructures have a net positive charge and CO binds to the most cationic Au atom of a cluster. Interactions of Aunand CO with magnetite (111) show many similarities with those on hematite (0001) surface. The influence of the substrate relaxation effects on adsorption energy is also discussed.

CO adsorption, oxidation and carbonate formation mechanisms on Fe3O4 surfaces

By means of density functional theory calculations that account for the on-site Coulomb interaction via a Hubbard term (DFT+U), we systematically investigated CO adsorption on Fe₃O₄ surfaces at different coverages. It has been found that more than one CO can coadsorb on one surface iron atom on both Fe_tet1 and Fe_oct2 terminations of Fe₃O₄(111). The uncapped oxygen atom is the active site for CO oxidation on both Fe_tet1 and Fe_oct2 terminations of Fe₃O₄(111). For Fe₃O₄(110), two CO molecules prefer to coadsorb on one surface iron atom on the A layer; CO prefers to adsorb at the bridge site of the surface octahedral iron atoms at low coverage, while CO prefers to adsorb at the surface tetrahedral iron atom at high coverage on the B layer. It has been found that the surface oxygen atom which is not coordinated to the tetrahedral iron atom is the active site for CO oxidation on the B termination of Fe₃O₄(001). On the Fe₃O₄ surfaces, the formation of carbonate has been found to be very stable thermodynamically, which agrees well with experiments. The adsorption mechanism has been analyzed on the basis of projected density of states (PDOS).

Adsorption of gold subnano-structures on a magnetite(111) surface and their interaction with CO

Gold deposited on iron oxide surfaces can catalyze the oxidation of carbon monoxide.