| 1. |
- Anil, Athira, et al.
(author)
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Effect of pore mesostructure on the electrooxidation of glycerol on Pt mesoporous catalysts
- 2023
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In: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 11:31, s. 16570-16577
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Journal article (peer-reviewed)abstract
- Glycerol is a renewable chemical that has become widely available and inexpensive due to the increased production of biodiesel. Noble metal materials have shown to be effective catalysts for the production of hydrogen and value-added products through the electrooxidation of glycerol. In this work we develop three platinum systems with distinct pore mesostructures, e.g., hierarchical pores (HP), cubic pores (CP) and linear pores (LP); all with high electrochemically active surface area (ECSA). The ECSA-normalized GEOR catalytic activity of the systems follows HPC > LPC > CPC > commercial Pt/C. Regarding the oxidation products, we observe glyceric acid as the main three-carbon product (3C), with oxalic acids as the main two-carbon oxidation product. DFT-based theoretical calculations support the glyceraldehyde route going through tartronic acid towards oxalic acid and also help understanding why the dihydroxyacetone (DHA) route is active despite the absence of DHA amongst the observed oxidation products.
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| 2. |
- B. Araujo, Rafael, et al.
(author)
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Adsorption energies on transition metal surfaces : towards an accurate and balanced description
- 2022
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 13
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Journal article (peer-reviewed)abstract
- Density functional theory predictions of binding energies and reaction barriers provide invaluable data for analyzing chemical transformations in heterogeneous catalysis. For high accuracy, effects of band structure and coverage, as well as the local bond strength in both covalent and non-covalent interactions, must be reliably described and much focus has been put on improving functionals to this end. Here, we show that a correction from higher-level calculations on small metal clusters can be applied to improve periodic band structure adsorption energies and barriers. We benchmark against 38 reliable experimental covalent and non-covalent adsorption energies and five activation barriers with mean absolute errors of 2.2 kcal mol−1, 2.7 kcal mol−1, and 1.1 kcal mol−1, respectively, which are lower than for functionals widely used and tested for surface science evaluations, such as BEEF-vdW and RPBE.
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| 3. |
- Fransson, Thomas, 1986-, et al.
(author)
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Evaluating the Impact of the Tamm–Dancoff Approximation on X-ray Spectrum Calculations
- 2024
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In: Journal of Chemical Theory and Computation. - 1549-9618 .- 1549-9626. ; 20:5, s. 2181-2191
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Journal article (peer-reviewed)abstract
- The impact of the Tamm–Dancoff approximation (TDA) for time-dependent density functional theory (TDDFT) calculations of X-ray absorption and X-ray emission spectra (XAS and XES) is investigated, showing small discrepancies in the excitation energies and intensities. Through explicit diagonalization of the TDDFT Hessian, XES was considered by using full TDDFT with a core-hole reference state. This has previously not been possible with most TDDFT implementations as a result of the presence of negative eigenvalues. Furthermore, a core–valence separation (CVS) scheme for XES is presented, in which only elements including the core-hole are considered, resulting in a small Hessian with the dimension of the number of remaining occupied orbitals of the same spin as the core-hole (CH). The resulting spectra are in surprisingly good agreement with the full-space counterpart, illustrating the weak coupling between the valence–valence and valence–CH transitions. Complications resulting from contributions from the discretized continuum are discussed, which can occur for TDDFT calculations of XAS and XES and for TDA calculations of XAS. In conclusion, we recommend that TDA be used when calculating X-ray emission spectra, and either CVS-TDA or CVS-TDDFT can be used for X-ray absorption spectra.
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| 4. |
- Koroidov, Sergey, et al.
(author)
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Chemisorbed oxygen or surface oxides steer the selectivity in Pd electrocatalytic propene oxidation observed by operando Pd L-edge X-ray absorption spectroscopy
- 2021
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In: Catalysis Science & Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 11:10, s. 3347-3352
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Journal article (peer-reviewed)abstract
- Controlled electrochemical oxidation of hydrocarbons to desired products is an attractive approach in catalysis. Here we study the electrochemical propene oxidation under operando conditions using Pd L-edge X-ray absorption spectroscopy (XAS) as a sensitive probe to elucidate surface processes occurring during catalysis. Together with ab initio multiple-scattering calculations, our XAS results enable assignment of characteristic changes of the Pd L-edge intensity and energy position in terms of a mechanistic understanding of the selective oxidation of propene. The results, supported by electrochemical density functional theory DFT simulations, show that in the potential range of 0.8–1.0 V vs. the reversible hydrogen electrode (RHE), selective oxidation of propene to acrolein and acrylic acid occurs on the metallic Pd surface. These reactions are proposed to proceed via the Langmuir–Hinshelwood mechanism. In contrast, for the potential range of 1.1–1.3 V vs. RHE, selective oxidation of propene to propylene glycol takes place on a Pd oxide surface.
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| 5. |
- LaRue, Jerry, et al.
(author)
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Symmetry-resolved CO desorption and oxidation dynamics on O/Ru(0001) probed at the C K-edge by ultrafast x-ray spectroscopy
- 2022
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 157:16
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Journal article (peer-reviewed)abstract
- We report on carbon monoxide desorption and oxidation induced by 400 nm femtosecond laser excitation on the O/Ru(0001) surface probed by time-resolved x-ray absorption spectroscopy (TR-XAS) at the carbon K-edge. The experiments were performed under constant background pressures of CO (6 × 10−8 Torr) and O2 (3 × 10−8 Torr). Under these conditions, we detect two transient CO species with narrow 2π* peaks, suggesting little 2π* interaction with the surface. Based on polarization measurements, we find that these two species have opposing orientations: (1) CO favoring a more perpendicular orientation and (2) CO favoring a more parallel orientation with respect to the surface. We also directly detect gas-phase CO2 using a mass spectrometer and observe weak signatures of bent adsorbed CO2 at slightly higher x-ray energies than the 2π* region. These results are compared to previously reported TR-XAS results at the O K-edge, where the CO background pressure was three times lower (2 × 10−8 Torr) while maintaining the same O2 pressure. At the lower CO pressure, in the CO 2π* region, we observed adsorbed CO and a distribution of OC–O bond lengths close to the CO oxidation transition state, with little indication of gas-like CO. The shift toward “gas-like” CO species may be explained by the higher CO exposure, which blocks O adsorption, decreasing O coverage and increasing CO coverage. These effects decrease the CO desorption barrier through dipole–dipole interaction while simultaneously increasing the CO oxidation barrier.
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| 6. |
- Moncada, Félix, 1989-, et al.
(author)
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A nuclear configuration interaction approach to study nuclear spin effects : an application to ortho- and para-3He2@C60
- 2024
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In: ChemPhysChem. - 1439-4235 .- 1439-7641. ; 25:4
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Journal article (peer-reviewed)abstract
- We introduce a non-orthogonal configuration interaction approach to investigate nuclear quantum effects on energies and densities of confined fermionic nuclei. The Hamiltonian employed draws parallels between confined systems and many-electron atoms, where effective non-Coulombic potentials represent the interactions of the trapped particles. One advantage of this method is its generality, as it offers the potential to study the nuclear quantum effects of various confined species affected by effective isotropic or anisotropic potentials. As a first application, we analyze the quantum states of two 3He atoms encapsulated in C60. At the Hartree–Fock level, we observe the breaking of spin and spatial symmetries. To ensure wavefunctions with the correct symmetries, we mix the broken-symmetry Hartree–Fock states within the non-orthogonal configuration interaction expansion. Our proposed approach predicts singly and triply degenerate ground states for the singlet (para-3He2@C60) and triplet (ortho-3He2@C60) nuclear spin configurations, respectively. The ortho-3He2@C60 ground state is 5.69 cm−1 higher in energy than the para-3He2@C60 ground state. The nuclear densities obtained for these states exhibit the icosahedral symmetry of the C60 embedding potential. Importantly, our calculated energies for the lowest 85 states are in close agreement with perturbation theory results based on a harmonic oscillator plus rigid rotor model of 3He2@C60.
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| 7. |
- Pettersson, Lars Gunnar Moody, 1951-, et al.
(author)
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The local structure of water from combining diffraction and X-ray spectroscopy
- 2022
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In: Journal of Non-Crystalline Solids: X. - : Elsevier BV. - 2590-1591. ; 14
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Journal article (peer-reviewed)abstract
- We build a large (~3400 structures) library of X-ray absorption (XAS) and X-ray emission (XES) spectra computed at high level, which together with their associated structures form the basis for a Monte Carlo fit to the experimental oxygen‑oxygen pair-distribution, XAS and XES spectra for ambient liquid water. The procedure results in weights giving the relative importance of each structure to reproduce the experimental properties. We show that the information content in the X-ray spectroscopic data is strongly complementary to that of X-ray diffraction, and dependent on specific structures that are still consistent with the diffraction data. We fit simultaneously to the X-ray spectroscopy and diffraction experimental data and obtain weights on each structure that give a structural distribution that is consistent with the three experimental datasets. These weights are applied to structural parameters characterizing the local environment of each structure and result in the emergence of more preferred values of these parameters.
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| 8. |
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| 9. |
- Takahashi, Osamu, et al.
(author)
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Dynamical and interference effects in X-ray emission spectroscopy of H-bonded water – origin of the split lone-pair peaks
- 2023
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In: Molecular Physics. - : Informa UK Limited. - 0026-8976 .- 1362-3028. ; 121:7-8
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Journal article (peer-reviewed)abstract
- We examine the effects of core-hole-induced dynamics and vibrational interference on computed x-ray emission spectra of H-bonded water. Two model pentamers were investigated, tetrahedral and distorted, representing possible local environments in proposed low- and high-density water. Core-hole-induced dynamics were considered in the simulations, and the semi-classical Kramers-Heisenberg (SCKH) scheme to convolute theoretical spectra was applied. We determine the origin of the split two peaks in XES of liquid water to be a combination of the initial H-bonding and subsequent dynamics, where we find faster dynamics for tetrahedrally bonded. We further find that H-bond acceptors move towards the core-excited molecule while donors move away and we analyse the origin of this dynamics in terms of charge-redistributions during the dynamics.We determine the origin of the split two peaks in X-ray emission spectra of liquid water to be a combination of the initial H-bonding and subsequent dynamics, where we find faster dynamics for tetrahedrally H-bonded water. We further find that H-bond acceptors move towards the core-excited molecule while donors move away and we analyse the origin of this dynamics in terms of charge-redistributions during the dynamics.
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| 10. |
- White, Jai, et al.
(author)
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Synergistic Bimetallic PdNi Nanoparticles : Enhancing Glycerol Electrooxidation While Preserving C3 Product Selectivity
- 2024
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In: ACS Applied Energy Materials. - 2574-0962. ; 7:5, s. 1802-1813
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Journal article (peer-reviewed)abstract
- Electrochemical conversion of glycerol offers a promising route to synthesize value-added glycerol oxidation products (GOPs) from an abundant biomass-based resource. While noble metals provide a low overpotential for the glycerol electrooxidation reaction (GEOR) and high selectivity toward three-carbon (C3) GOPs, their efficiency and cost can be improved by incorporating non-noble metals. Here, we introduce an effective strategy to enhance the performance of Pd nanoparticles for the GEOR by alloying them with Ni. The resulting PdNi nanoparticles show a significant increase in both specific activity (by almost 60%) and mass activity (by almost 35%) during the GEOR at 40 °C. Additionally, they exhibit higher resistance to deactivation compared to pure Pd. Analysis of the GOPs reveals that the addition of Ni into Pd does not compromise the selectivity, with glycerate remaining at around 60% of the product fraction and the other major product being lactate at around 30%. Density functional theory calculations confirm the reaction pathways and the basis for the higher activity of PdNi. This study demonstrates a significant increase in the GEOR catalytic performance while maintaining the selectivity for C3 GOPs, using a more cost-effective nanocatalyst.
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