Despite the great advances in synthesis and structural determination of atomically precise, thiolate-protected metal nanoclusters, our understanding of the driving forces for their colloidal ...stabilization is very limited. Currently there is a lack of models able to describe the thermodynamic stability of these 'magic-number' colloidal nanoclusters as a function of their atomic-level structural characteristics. Herein, we introduce the thermodynamic stability theory, derived from first principles, which is able to address stability of thiolate-protected metal nanoclusters as a function of the number of metal core atoms and thiolates on the nanocluster shell. Surprisingly, we reveal a fine energy balance between the core cohesive energy and the shell-to-core binding energy that appears to drive nanocluster stabilization. Our theory applies to both charged and neutral systems and captures a large number of experimental observations. Importantly, it opens new avenues for accelerating the discovery of stable, atomically precise, colloidal metal nanoclusters.
CO2 activation on bimetallic CuNi nanoparticles Austin, Natalie; Butina, Brandon; Mpourmpakis, Giannis
Progress in Natural Science/Progress in natural science,
10/2016, Volume:
26, Issue:
5
Journal Article
Peer reviewed
Open access
Density functional theory calculations have been performed to investigate the structural, electronic, and CO2 adsorption properties of 55-atom bimetallic Cu Ni nanoparticles（NPs） in core-shell and ...decorated architectures,as well as of their monometallic counterparts. Our results revealed that with respect to the monometallic Cu55 and Ni55parents, the formation of decorated Cu12Ni43 and core-shell Cu42Ni13 are energetically favorable. We found that CO2 chemisorbs on monometallic Ni55, core-shell Cu13Ni42, and decorated Cu12Ni43 and Cu43Ni12,whereas, it physisorbs on monometallic Cu55 and core-shell Cu42Ni13. The presence of surface Ni on the NPs is key in strongly adsorbing and activating the CO2 molecule（linear to bent transition and elongation of C=O bonds）. This activation occurs through a charge transfer from the NPs to the CO2 molecule, where the local metal d-orbital density localization on surface Ni plays a pivotal role. This work identifies insightful structureproperty relationships for CO2 activation and highlights the importance of keeping a balance between NP stability and CO2 adsorption behavior in designing catalytic bimetallic NPs that activate CO2.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Dispersion-corrected density functional theory calculations were performed to investigate the adsorption of furan, furfural, furfuryl alcohol, and 2-methylfuran as well as the reaction barriers for ...their interconversion. The most stable configuration for furan, furfural, furfuryl alcohol, and 2-methylfuran entails the furan ring lying flat on the surface, centered over a hollow site. We performed an elementary step analysis for the reaction of furfural to furan, furfuryl alcohol, and 2-methylfuran. Thermodynamics favors the production of furan and CO. The activation energy for furfural reduction to furfuryl alcohol is lower than that for its decarbonylation to furan. The formation of 2-methylfuran occurs via dehydration of furfuryl alcohol or a dehydrogenation pathway through a methoxy intermediate. Our findings are in agreement with recently reported experimental results.
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IJS, KILJ, NUK, PNG, UL, UM
Single-atom catalysts (SACs), containing under-coordinated single metal atoms bound to the surface of supports, are promising heterogeneous catalysts due to their intrinsic catalytic properties and ...efficient utilization of noble metal atoms. However, SAC stability under catalytic operation is questioned due to the tendency of metals to sinter (aggregation). Herein, we perform density functional theory (DFT) calculations to investigate the metal–support interactions (MSIs) of a series of transition-metal atoms supported on three common oxide supports (γ-Al2O3, MgO, and MgAl2O4). Moreover, utilizing the DFT results and genetic programming, we develop a predictive model for the strength of MSIs using simple properties of both the SACs and supports. Finally, we introduce criteria for the synthetic accessibility of SACs based on thermodynamic arguments. Our computational work can guide experiments by identifying combinations of metals and oxides that can potentially lead to highly stable (and catalytically durable) SACs.
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IJS, KILJ, NUK, PNG, UL, UM
Ligand-protected metal nanoclusters (NCs) are organic-inorganic nanostructures, exhibiting high stability at specific "magic size" compositions and tunable properties that make them promising ...candidates for a wide range of nanotechnology-based applications. Synthesis and characterization of these nanostructures has been achieved with atomic precision, offering great opportunities to study the origin of new physicochemical property emergence at the nanoscale using theory and computation. In this
Frontier
article, we highlight the recent advances in the field of ligand-protected metal NCs, focusing on stability theories on monometallic and heterometal doped NCs, and NC structure prediction. Furthermore, we discuss current challenges on predicting previously undiscovered NCs and propose future steps to advance the field through applying first principles calculations, machine learning, and data-science-based approaches.
Developing a centralized database for ligand-protected nanoclusters can fuel machine learning and data-science-based approaches towards theoretical structure prediction.
Heterometal doping is a promising avenue toward tailoring properties of ligand-protected metal nanoclusters for specific applications. Though successful doping has been demonstrated in several ...structures, the underlying reasons for the dopant preference on occupying specific locations on the nanocluster with different concentrations remain unclear. In this study we apply our thermodynamic stability model, originally developed for ligand-protected monometallic nanoclusters, to rationalize the synthetic accessibility, dopant location, and concentrations of various heterometals on ligand-protected Au nanoclusters. Importantly, we demonstrate that the thermodynamic stability theory is a significant step forward in accurately describing doping effects on nanoclusters using first-principles calculations. With our computational predictions being in excellent agreement with a series of experiments, we introduce the thermodynamic stability theory as a new method for bimetallic nanocluster prediction.
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IJS, KILJ, NUK, PNG, UL, UM
7.
Determination of Proton Affinities and Acidity Constants of Sugars Feng, Shuting; Bagia, Christina; Mpourmpakis, Giannis
The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory,
06/2013, Volume:
117, Issue:
24
Journal Article
Peer reviewed
Proton transfer reactions play a key role in the conversion of biomass derived sugars to chemicals. In this study, we employ high level ab initio theoretical methods, in tandem with solvation effects ...to calculate the proton affinities (PA) and acidity constants (pK a) of various d-glucose and d-fructose tautomers (protonation–deprotonation processes). In addition, we compare the theoretically derived pH values of sugar solutions against experimentally measured pH values in our lab. Our results demonstrate that the protonation of any of the O atoms of the sugars is thermodynamically preferred without any significant variation in the PA values. Intramolecular hydrogen transfers, dehydration reactions, and ring-opening processes were observed, resulting from the protonation of specific hydroxyl groups on the sugars. Regarding the deprotonation processes (pK a), we found that the sugars’ anomeric hydroxyls exhibit the highest acidity. The theoretically calculated pH values of sugar solutions are in excellent agreement with experimental pH measurements at low sugar concentrations. At higher sugar concentrations the calculations predict less acidic solutions than the experiments. In this case, we expect the sugars to act as solvents increasing the proton solvation energy and the acidity of the solutions. We demonstrated through linear relationships that the pK a values are correlated with the relative stability of the conjugate bases. The latter is related to hydrogen bonding and polarization of the C–O– bond. A plausible explanation for the good performance of the direct method in calculating the pK a values of sugars can be the presence of intramolecular hydrogen bonds on the conjugate base. Both theory and experiments manifest that fructose is a stronger acid than glucose, which is of significant importance in self-catalyzed biomass-relevant dehydration reactions.
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IJS, KILJ, NUK, PNG, UL, UM
Gold-based materials hold promise in electrocatalytic reduction of CO2 to fuels. However, the polydispersity of conventional gold nanostructures limits mechanistic studies. Here, we report two types ...of atomically precise Au25 nanoclusters (1 nm) with distinct morphology (i.e., nanosphere and nanorod) for CO2 reduction catalysis. The Au25 nanosphere exhibits higher Faradaic efficiency for CO with higher formation rates compared to the Au25 nanorod. First-principles calculations reveal that the negative charge and the energetically favorable removal of one ligand to generate an active site on the nanosphere can better stabilize the important *COOH intermediate in CO2 electroreduction.
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IJS, KILJ, NUK, PNG, UL, UM
A multiscale theoretical approach was used for the investigation of hydrogen storage in the recently synthesized carbon nanoscrolls. First, ab initio calculations at the density functional level of ...theory (DFT) were performed in order to (a) calculate the binding energy of H2 molecules at the walls of nanoscrolls and (b) fit the parameters of the interatomic potential used in Monte Carlo simulations. Second, classical Monte Carlo simulations were performed for estimating the H2 storage capacity of “experimental size” nanoscrolls containing thousands of atoms. Our results show that pure carbon nanoscrolls cannot accumulate hydrogen because the interlayer distance is too small. However, an opening of the spiral structure to approximately 7 Å followed by alkali doping can make them very promising materials for hydrogen storage application, reaching 3 wt % at ambient temperature and pressure.
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Using density functional theory (DFT) calculations, we investigated the electrochemical reduction of CO2 and the competing H2 evolution reaction on ligand-protected Au25 nanoclusters (NCs) of ...different charge states, Au25(SR)18q (q = −1, 0, +1). Our results showed that regardless of charge state, CO2 electroreduction over Au25(SR)18q NCs was not feasible because of the extreme endothermicity to stabilize the carboxyl (COOH) intermediate. When we accounted for the removal of a ligand (both –SR and –R) from Au25(SR)18q under electrochemical conditions, surprisingly we found that this is a thermodynamically feasible process at the experimentally applied potentials with the generated surface sites becoming active centers for electrocatalysis. In every case, the negatively charged NCs, losing a ligand from their surface during electrochemical conditions, were found to significantly stabilize the COOH intermediate, resulting in dramatically enhanced CO2 reduction. The generated sites for CO2 reduction were also found to be active for H2 evolution, which agrees with experimental observations that these two processes compete. Interestingly, we found that the removal of an –R ligand from the negatively charged NC, resulted in a catalyst that was both active and selective for CO2 reduction. This work highlights the importance of both the overall charge state and generation of catalytically active surface sites on ligand-protected NCs, while elucidating the CO2 electroreduction mechanisms. Overall, our work rationalizes a series of experimental observations and demonstrates pathways to convert a very stable and catalytically inactive NC to an active electrocatalyst.
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