An intermetallic nanocluster containing 44 metal atoms, Au24Ag20(2-SPy)4(PhCC)20Cl2, was successfully synthesized and structurally characterized by single-crystal analysis and density funtional ...theory computations. The 44 metal atoms in the cluster are arranged as a concentric three-shell Au12@Ag20@Au12 Keplerate structure having a high symmetry. For the first time, the co-presence of three different types of anionic ligands (i.e., phenylalkynyl, 2-pyridylthiolate, and chloride) was revealed on the surface of metal nanoclusters. Similar to thiolates, alkynyls bind linearly to surface Au atoms using their σ-bonds, leading to the formation of two types of surface staple units (PhCC-Au-L, L = PhCC– or 2-pyridylthiolate) on the cluster. The co-presence of three different surface ligands allows the site-specific surface and functional modification of the cluster. The lability of PhCC– ligands on the cluster was demonstrated, making it possible to keep the metal core intact while removing partial surface capping. Moreover, it was found that ligand exchange on the cluster occurs easily to offer various derivatives with the same metal core but different surface functionality and thus different solubility.
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Demonstrated herein are the preparation and crystallographic characterization of the family of fcc silver nanoclusters from Nichol’s cube to Rubik’s cube and beyond via ligand-control (thiolates and ...phosphines in this case). The basic building block is our previously reported fcc cluster Ag14(SPhF2)12(PPh3)8 (1). The metal frameworks of Ag38(SPhF2)26(PR′3)8 (2 2 ) and Ag63(SPhF2)36(PR′3)8+ (2 3 ), where HSPhF2 = 3,4-difluorothiophenol and R′ = alkyl/aryl, are composed of 2 × 2 = 4 and 2 × 2 × 2 = 8 metal cubes of 1, respectively. All serial clusters share similar surface structural features. The thiolate ligands cap the six faces and the 12 edges of the cube (or half cube) while the phosphine ligands are terminally bonded to its eight corners. On the basis of the analysis of the crystal structures of 1, 2 2 , and 2 3 , we predict the next “cube of cubes” to be Ag172(SR)72(PR′3)8 (3 3 ), in the evolution of growth of this cluster sequence.
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In this study, we investigate the hydrogenation reaction of levulinic acid to 4-hydroxypentanoic acid on ligand-modified Pt(111) using DFT. Modifying nanoparticle surfaces with ligands can have ...beneficial effects on the desired reaction such as improved selectivity or lower activation energies. The
N
3
,
N
3
-dimethyl-
N
2
-(quinolin-2-yl)propane-1,2-diamine (AQ) ligand was selected to modify the surface, since it combines good surface adsorption properties with functional groups that can influence the reaction. The adsorption geometry of the AQ ligand was studied as well as the co-adsorption of a second AQ ligand for the possibility of self-assembly. We found that dissociated hydrogen from the Pt(111) surface can protonate the AQ ligand and discuss the role this plays on the mechanism of the hydrogenation reaction of levulinic acid (LA). By comparing the ligand-modified Pt(111) surface to the bare Pt(111) surface we show that the reaction changes from a step-wise to a concerted mechanism due to the influence of the ligand molecule. This demonstrates the effect that ligand-modified surfaces can have on catalyzing reactions and shows that desired reactions can be achieved by tuning the reaction environment.
In this study, we investigate the hydrogenation reaction of levulinic acid to 4-hydroxypentanoic acid on ligand-modified Pt(111) using DFT.
Multi-component heterogeneous catalysts are among the top candidates for converting greenhouse gases into valuable compounds. Combinations of Cu, Zn, and ZrO2 (CZZ) have emerged as promisingly ...efficient catalysts for CO2 hydrogenation to methanol. To explore the catalytic mechanism, density functional theory (DFT) calculations and the energetic span model (ESM) were used to study CO2 conversion routes to methanol on CuZn–ZrO2 interfaces with a varying Zn content. Our results demonstrate that the presence of Zn sites at the interface improves CO2 binding. However, the adsorption and activation energies are insensitive to Zn concentration. The calculations also show that the hydrogenation of adsorbate oxygen atoms at the interface is kinetically more favourable and requires hydrogen spillover from the metal to the zirconia. This leads to barriers that are lower than those reported on interface or metal-only sites in previous literature. While DFT calculations alone are unable to identify which one of the competing pathways is more favourable, the ESM model predicts that the carboxyl pathway has a higher turnover frequency than the formate route. Our findings also show the importance of considering effects such as hydrogen spillover which take place at a metal-oxide interface when modelling complex catalytic environments.
Multi-component heterogeneous catalysts are among the top candidates for converting greenhouse gases into valuable compounds. Combinations of Cu, Zn, and ZrO 2 (CZZ) have emerged as promisingly ...efficient catalysts for CO 2 hydrogenation to methanol. To explore the catalytic mechanism, density functional theory (DFT) calculations and the energetic span model (ESM) were used to study CO 2 conversion routes to methanol on CuZn–ZrO 2 interfaces with a varying Zn content. Our results demonstrate that the presence of Zn sites at the interface improves CO 2 binding. However, the adsorption and activation energies are insensitive to Zn concentration. The calculations also show that the hydrogenation of adsorbate oxygen atoms at the interface is kinetically more favourable and requires hydrogen spillover from the metal to the zirconia. This leads to barriers that are lower than those reported on interface or metal-only sites in previous literature. While DFT calculations alone are unable to identify which one of the competing pathways is more favourable, the ESM model predicts that the carboxyl pathway has a higher turnover frequency than the formate route. Our findings also show the importance of considering effects such as hydrogen spillover which take place at a metal-oxide interface when modelling complex catalytic environments.
Multi-component heterogeneous catalysts are among the top candidates for converting greenhouse gases into valuable compounds. Combinations of Cu, Zn, and ZrO
2
(CZZ) have emerged as promisingly ...efficient catalysts for CO
2
hydrogenation to methanol. To explore the catalytic mechanism, density functional theory (DFT) calculations and the energetic span model (ESM) were used to study CO
2
conversion routes to methanol on CuZn-ZrO
2
interfaces with a varying Zn content. Our results demonstrate that the presence of Zn sites at the interface improves CO
2
binding. However, the adsorption and activation energies are insensitive to Zn concentration. The calculations also show that the hydrogenation of adsorbate oxygen atoms at the interface is kinetically more favourable and requires hydrogen spillover from the metal to the zirconia. This leads to barriers that are lower than those reported on interface or metal-only sites in previous literature. While DFT calculations alone are unable to identify which one of the competing pathways is more favourable, the ESM model predicts that the carboxyl pathway has a higher turnover frequency than the formate route. Our findings also show the importance of considering effects such as hydrogen spillover which take place at a metal-oxide interface when modelling complex catalytic environments.
Multi-component heterogeneous catalysts are among the top candidates for converting greenhouse gases into valuable compounds.
We report a simple synthesis of silver:glutathione (Ag:SG) clusters using a cyclic reduction under oxidative conditions. Two syntheses are described which lead to solutions containing well-defined ...Ag31(SG)19 and Ag15(SG)11 clusters that have been characterized by mass spectrometry. The optical properties of silver:glutathione (Ag:SG) cluster solutions have been investigated experimentally. In particular, the solution containing Ag15(SG)11 clusters shows a bright and photostable emission. For Ag31(SG)19 and Ag15(SG)11 clusters, the comparison of experimental findings with DFT and TDDFT calculations allowed us to reveal the structural and electronic properties of such low nuclearity liganded silver clusters.
The electronic structure of two recently crystallographically solved, thiolate-phosphine protected silver clusters Ag14 and Ag16 are analyzed via density functional theory (DFT) and their optical ...excitations are analyzed from time-dependent DFT perturbation theory. Both clusters can be characterized as having the S(2) free-electron configuration in the metal core, which is the first time such a configuration is confirmed for structurally known ligand-protected noble metal clusters. However, their different core shapes and ligand layer induce significantly different optical spectra. Performance of gradient-corrected DFT functionals is discussed and it is shown that the asymptotically correct Leeuwen-Baerends LB94 functional reproduces the optical spectrum of Ag14 in a good agreement with experiment. Choice of the functional becomes important for clusters where the optical transitions are dominated by the electron-rich ligand layer.
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