Author: Lars Gell

Exploring CO2 hydrogenation to methanol at a CuZn–ZrO2 interface via DFT calculations

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 …

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Embryonic Growth of Face-Center-Cubic Silver Nanoclusters Shaped in Nearly Perfect Half-Cubes and Cubes.

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] (22) and [Ag63(SPhF2)36(PR′3)8]+ (23), 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 phosp…

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An Intermetallic Au24Ag20 Superatom Nanocluster Stabilized by Labile Ligands

An intermetallic nanocluster containing 44 metal atoms, Au24Ag20(2-SPy)4(PhC≡C)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 (PhC≡C-Au-L, L …

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All-thiol-stabilized Ag44 and Au12Ag32 nanoparticles with single-crystal structures

Noble metal nanoparticles stabilized by organic ligands are important for applications in assembly, site-specific bioconjugate labelling and sensing, drug delivery and medical therapy, molecular recognition and molecular electronics, and catalysis. Here we report crystal structures and theoretical analysis of three Ag44(SR)30 and three Au12Ag32(SR)30 intermetallic nanoclusters stabilized with fluorinated arylthiols (SR=SPhF, SPhF2 or SPhCF3). The nanocluster forms a Keplerate solid of concentric icosahedral and dodecahedral atom shells, protected by six Ag2(SR)5 units. Positive counterions in the crystal indicate a high negative charge of 4(-) per nanoparticle, and density functional theory…

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Ag44(SeR)30: A Hollow Cage Silver Cluster with Selenolate Protection.

Selenolate protected, stable and atomically precise, hollow silver cluster was synthesized using solid state as well as solution state routes. The optical absorption spectrum shows multiple and sharp features similar to the thiolated Ag44 cluster, Ag44(SR)30 whose experimental structure was reported recently. High-resolution electrospray ionization mass spectrometry (HRESI MS) shows well-defined molecular ion features with two, three, and four ions with isotopic resolution, due to Ag44(SePh) 30. Additional characterization with diverse tools confirmed the composition. The closed-shell 18 electron superatom electronic structure, analogous to Ag44(SR)30 stabilizes the dodecahedral cage with a…

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Influence of a Cu–zirconia interface structure on CO2 adsorption and activation

CO2 adsorption and activation on a catalyst are key elementary steps for CO2 conversion to various valuable products. In the present computational study, we screened different Cu–ZrO2 interface structures and analyzed the influence of the interface structure on CO2 binding strength using density functional theory calculations. Our results demonstrate that a Cu nanorod favors one position on both tetragonal and monoclinic ZrO2 surfaces, where the bottom Cu atoms are placed close to the lattice oxygens. In agreement with previous calculations, we find that CO2 prefers a bent bidentate configuration at the Cu–ZrO2 interface and the molecule is clearly activated being negatively charged. Strain…

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Effect of atomic layer deposited zinc promoter on the activity of copper-on-zirconia catalysts in the hydrogenation of carbon dioxide to methanol

Funding Information: The work at Aalto University has been financially supported by the Academy of Finland (COOLCAT consortium, decision no. 329977 and 329978 ; ALDI consortium, decision no. 331082 ). This work made use of Aalto University Bioeconomy, OtaNano and RawMatters infrastructure. Hannu Revitzer (Aalto University) is thanked for the ICP-OES analysis, Aalto workshop people (especially Seppo Jääskeläinen) for working on the reactor modifications. The DFT calculations were made possible by computational resources provided by the CSC — IT Center for Science, Espoo, Finland ( https://www.csc.fi/en/ ) and computer capacity from the Finnish Grid and Cloud Infrastructure (urn:nbn:fi:resear…

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Influence of a Cu–zirconia interface structure on CO2 adsorption and activation

CO2 adsorption and activation on a catalyst are key elementary steps for CO2 conversion to various valuable products. In the present computational study, we screened different Cu–ZrO2 interface structures and analyzed the influence of the interface structure on CO2 binding strength using density functional theory calculations. Our results demonstrate that a Cu nanorod favors one position on both tetragonal and monoclinic ZrO2 surfaces, where the bottom Cu atoms are placed close to the lattice oxygens. In agreement with previous calculations, we find that CO2 prefers a bent bidentate configuration at the Cu–ZrO2 interface and the molecule is clearly activated being negatively charged. Strain…

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Theoretical Analysis of the M12Ag32(SR)404– and X@M12Ag32(SR)304– Nanoclusters (M = Au, Ag; X = H, Mn)

We analyze the electronic structure and optical properties of the recently reported, structurally known M12Ag32(SR)304– clusters (M = Au, Ag) by using density functional theory and time-dependent density functional perturbation theory. Effects of the chemical changes in the metal core, charge of the cluster, and nature of the thiolate ligand on the electronic structure and optical absorption are reported. In addition, doping the metal core with a magnetic transition metal atom (Mn) or hydrogen (protons) is discussed. Although all these clusters can be considered as 18-electron superatoms with a shell configuration 1S2 1P6 1D10, we find that the optical spectrum is sensitive to the charge st…

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Ligand assisted hydrogenation of levulinic acid on Pt(111) from first principles calculations

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 N3,N3-dimethyl-N2-(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(…

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Superatomic S2 Silver Clusters Stabilized by a Thiolate–Phosphine Monolayer: Insight into Electronic and Optical Properties of Ag14(SC6H3F2)12(PPh3)8 and Ag16(SC6H3F2)14(DPPE)4

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 S2 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 L…

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CCDC 1530605: Experimental Crystal Structure Determination

Related Article: Huayan Yang, Juanzhu Yan, Yu Wang, Haifeng Su, Lars Gell, Xiaojing Zhao, Chaofa Xu, Boon K. Teo, Hannu Häkkinen , and Nanfeng Zheng|2017|J.Am.Chem.Soc.|139|31|doi:10.1021/jacs.6b10053

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CCDC 1530607: Experimental Crystal Structure Determination

Related Article: Huayan Yang, Juanzhu Yan, Yu Wang, Haifeng Su, Lars Gell, Xiaojing Zhao, Chaofa Xu, Boon K. Teo, Hannu Häkkinen , and Nanfeng Zheng|2017|J.Am.Chem.Soc.|139|31|doi:10.1021/jacs.6b10053

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CCDC 1530606: Experimental Crystal Structure Determination

Related Article: Huayan Yang, Juanzhu Yan, Yu Wang, Haifeng Su, Lars Gell, Xiaojing Zhao, Chaofa Xu, Boon K. Teo, Hannu Häkkinen , and Nanfeng Zheng|2017|J.Am.Chem.Soc.|139|31|doi:10.1021/jacs.6b10053

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CCDC 1530604: Experimental Crystal Structure Determination

Related Article: Huayan Yang, Juanzhu Yan, Yu Wang, Haifeng Su, Lars Gell, Xiaojing Zhao, Chaofa Xu, Boon K. Teo, Hannu Häkkinen , and Nanfeng Zheng|2017|J.Am.Chem.Soc.|139|31|doi:10.1021/jacs.6b10053

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