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International audience; The hydrodeoxygenation (HDO) is a fundamental step in the production of biofuels from lignin, and the catalyst type and reaction conditions can play an important role. In this work, Co nanoparticles finely dispersed in the porosity of SBA-15 stand out a high selectivity toward deoxygenated products (63 % of methylcyclohexenes and 16 % of methylcyclohexane) in the HDO of m-cresol (30 bar of pressure, temperature of 350 degrees C). The effect of co-feeding CO and CO2, which can be present in the pyrolysis gas after transformation of carboxylic acids, was investigated. An unexpected positive effect on the stability of the catalyst was observed when CO2 was added in the feed stream. On the contrary, the presence of CO led to a strong decrease of the m-cresol conversion. These experimental findings are supported by DFT calculations which show that the m-cresol is much more strongly adsorbed than CO2 at the Co@SiO2 interface while the interaction energy of CO is close to the one of m-cresol.

Biomass-based renewable hydrocarbon fuel is a complex mix that contains many oxygenating substances, in particular phenolics, which leads to adverse consequences such as reduced engine energy performance and increased toxic gas emissions. Density functional theory calculations were found to be useful to identify the efficient formulations of adsorbents in various selective trapping applications, and particularly for separating phenol from toluene for biofuel purification. Various interaction modes of the considered molecules on different adsorbents, such as Fe, Co, Ni and Cu@silica, were systematically investigated to show that silica surfaces, especially Cu@silica, are potentially selective towards phenol versus toluene.

D.E. acknowledges the financial support given by the Spanish Ministry of Science, Innovation, and Universities (MCIU) under grant nos. PID2019-106383GB-C41 and RED2018-102612-T (MALTA Consolider-Team network) and by Generalitat Valenciana under Grant Prometeo/2018/123 (EFIMAT). R.F. and A. Lobato are grateful to financial support from Spanish MCIU under grant PGC2018-094814-B-C22. We would like to thank TGCC under the allocation 2020-A0080910433 made by GENCI, the PMMS (Pôle Messin de Modélisation et de Simulation), the Tirant supercomputer (Universitat de Valencia), and the MALTA-Consolider facilities for providing us the computational resources. S.G. and M.B. also acknowledge financial support through the COMETE project (Conception in silico de Matériaux pour l’Environnement et l’Energie) co-funded by the European Union under the program “FEDERFSE Lorraine et Massif des Vosges 2014–2020”.

Biofuels may contain phenolic molecules, which are toxic for humans and can significantly affect engine performance. In this context, amorphous silica surfaces are attractive since they have the po...

The spin-crossover [Fe(bt)(NCS)2]2(bpm) complex is studied using spin-polarized density functional theory within the generalized gradient approximation, the Hubbard U and the weak van der Waals interactions in conjunction with the projector augmented wave method in its molecular and periodic arrangements. It is shown that the considered complex has three magnetic configurations [high spin state (HS)–HS, HS–low spin state (LS), and LS–LS] corresponding to those observed experimentally after two transition temperatures [Formula: see text] of 163 K and [Formula: see text] of 197 K. For the HS–HS magnetic state, we found that the two Fe centers are antiferromagnetically coupled for both molecular and periodic structures in good agreement with the experimental observations. Our results show that the computed total energy difference between the magnetic state configurations of the considered Fe2 complex is significantly smaller compared to those reported in the literature for other mono- or binuclear compounds.

Using first-principles calculations, we have studied the structural and electronic properties of ZrOX (X = S, Se, and Te) monolayers and their van der Waals heterostructures in the tetragonal structure. Our results show that these monolayers are dynamically stable and are semiconductors with electronic bandgaps ranging from 1.98 to 3.16 eV as obtained with the GW approximation. By computing their band edges, we show that ZrOS and ZrOSe are of interest for water splitting applications. In addition, the van der Waals heterostructures formed by these monolayers show a type I band alignment for ZrOTe/ZrOSe and a type II alignment for the other two heterostructures, making them potential candidates for certain optoelectronic applications involving electron/hole separation.

The upgrading of lignin-derived bio-oils involves a HydroDeOxygenation (HDO) reaction through either the Hydrogenation (Hyd) or the Direct DeOxygenation (DDO) route, the latter limiting hydrogen consumption. Herein, dispersion-corrected DFT has been used to evaluate the adsorption behavior of phenol (as a representative model of bio-oils) and two by-products (water and CO) over various crystalline and amorphous silica surfaces to evaluate their potential selectivity (DDO/Hyd) and efficiency (low inhibiting effect) for HDO processing. Phenol can adsorb through three modes, flat π-interaction, flat O-interaction or perpendicular O-interaction. All crystalline surfaces show a preference for the flat π-interaction, which is expected to promote the Hyd route. Over amorphous surfaces the flat O-interaction dominates, and a very specific and strong interaction (around −120 kJ/mol) was found on SiO2-3.3 and SiO2-2.0 surfaces where the phenol molecule loses its aromaticity, which is very promising for its degradation under catalytic conditions. In addition, this makes those surfaces very efficient to adsorb selectively phenol in presence of water and CO. Remarkably, on all silica surfaces, the interaction energy of CO is nearly negligible, which makes them more attractive for HDO process compared to sulfide catalysts with respect to the inhibiting effect criteria.

The GW approximation for electronic excitations is considered computationally hard because its CPU time scales as O ( N 4 ) with the number N of atoms in the unit cell. The space time approach to this approximation scales, in principle, as O ( N 3 ) , but for crystals it is nearly impossible to exploit this feature because it requires too much computer memory. Here we remove this memory bottleneck by restricting the screened Coulomb interaction in the GW self-energy to its Nyquist content. This reduces both the needed memory and the CPU time by several orders of magnitude, while keeping satisfactory agreement with experimentally measured gaps. Our method allows exploiting the O ( N 3 ) scaling feature of the GW space time approach with modest computational resources and it will facilitate the computation of the fundamental gaps of organic semiconductors.

Transition metals (Co, Ni, or Cu) systems supported on amorphous silica are promising materials for their unique surface chemical reactivity. Despite many investigations, the transition metal-support interactions for this type of materials are not yet well understood at the molecular level. In this work, periodic density functional theory calculations, were performed to investigate systematically the interaction between Co, Ni, or Cu species (monomers and clusters) and amorphous silica surfaces with densities of 3.3 and 4.6 OH/nm2. It is shown that the geometry, energetic stability, and magnetic properties of transition metal species deposited on amorphous silica surfaces depend strongly of the number of M-O-Si groups and, in few cases, of the number of M-OH-Si groups, with sometimes a strong effect on the silica surface that induces a reorganization of the silanol groups. Among monomers, cobalt is found to be the most stable on the silica surface while among clusters, the Ni cluster is the most strongly adsorbed. The magnetic moments of the adsorbed transition metal clusters on silica surface are found to be reduced with respect to their corresponding free clusters for Co and Ni.

Standard solid-state methods produced black crystals of the compounds BaCu0.43(3)Te2 and BaAg0.77(1)Te2 at 1173 K; the crystal structures of each were established using single-crystal X-ray diffraction data. Both crystal structures are modulated. The compound BaCu0.43(3)Te2 crystallizes in the monoclinic superspace group P2(αβ1/2)0, having cell dimensions of a = 4.6406(5) A, b = 4.6596(5) A, c = 10.362(1) A, β = 90.000(9)°, and Z = 2 and an incommensurate vector of q = 0.3499(6)b* + 0.5c*. The compound BaAg0.77(1)Te2 crystallizes in the orthorhombic P21212(α00)000 superspace group with cell dimensions of a = 4.6734(1) A, b = 4.6468(1) A, c = 11.1376(3) A, and Z = 2 and an incommensurate vector of q = 0.364(2)a*. The asymmetric unit of the BaCu0.43(3)Te2 structure comprises eight crystallographically independent sites; that for BaAg0.77(1)Te2 comprises four. In these two structures, each of the M (M = Cu, Ag) atoms is connected to four Te atoms to make two-dimensional layers of [MxTe4/4]n- that are separated by layers of Ba atoms and square nets of Te. A Raman spectroscopic study at 298(2) K on a pelletized polycrystalline sample of BaAg0.8Te2 shows the presence of Ag-Te (83, 116, and 139 cm-1) and Ba-Te vibrations (667 and 732 cm-1). A UV-vis-NIR spectroscopic study on a powdered sample of BaAg0.8Te2 shows the semiconducting nature of the compound with a direct band gap of 1.0(2) eV, consistent with its black color. DFT calculations give a pseudo bandgap with a weak value of the DOS at the Fermi level.

Standard solid-state methods produced black crystals of the compounds BaCu

Iron over silica catalytic systems have attracted considerable attention due to their activity and selectivity in different reactions, for instance, in the hydrodeoxygenation process. Here, the grafting mechanisms of iron under various forms (one atom, two atoms, or a cluster) on silica surfaces are studied using ab initio calculations. Various geometries with different locations of iron on the silica structure have been investigated, and it is found that a strong interaction between iron and the silanol groups takes place, mostly driven by the formation of Fe-O-Si bonds, and in few cases by nearby surface OH groups, creating Fe-OH-Si bonds. For the cluster, we show that the most favorable adsorption mode induces a strong effect on the silica surface accompanied with a large charge transfer, making it very stable and promising for a large panel of applications.

A better separation and purification of organic acids in liquid phase is a key for a more performing biorefinery industry. Herein, amorphous silica surfaces with a density of silanol ranging between 1.1 and 7.2 OH · nm−2 are investigated to separate glucose molecules from the fermentation broths. Different interaction modes of glucose and itaconic acid on the considered silica surfaces at various silanol sites are systematically investigated using periodic density functional theory. Our results show that the surfaces with a silanol density of 2.0 to 7.2 OH · nm−2 are potentially selective for glucose adsorption in comparison with itaconic acid.

The catalytic hydrodeoxygenation (HDO) of lignin is an important route to produce green aromatics. Herein we study the adsorption of key phenolic molecules (phenol, catechol, guaiacol, anisole) over various metallic nanoparticles (NP) (Ni, Cu, Co, Fe) supported over amorphous silica, by the periodic spin polarized density functional theory (DFT). CO and water are potential inhibiting molecules present in the lignin pyrolysis gas. Therefore their competing adsorption is also studied in details. Our calculations show that the oxygenated compounds have a stronger interaction at the interface between the NP cluster and the silica for all the studied metals. By comparing the resulting adsorption energies, we found that the Ni13@silica catalyst is the most attractive one for oxygenated molecules. The most stable configuration is a phenol adsorption at the interface through the OH group with the silica surface and the aromatic ring with the transition metal cluster. In addition, we show that the adsorption of the oxygenated compounds is not impacted by the presence of inhibiting molecules on Fe13@silica, Co13@silica and Ni13@silica catalysts. This type of DFT investigation appears to be useful to suggest suitable formulations for an optimal HDO of lignin.

International audience; The electronic and optical properties of crystalline tetrathienophenazine derivatives (l-TTP, m-TTP, t-TTP) and their four fluorinated and brominated derivatives are predicted using density functional theory within the generalized gradient approximation and including the van der Waals weak interactions. We analyze how the position of sulfur atoms and fluorination and bromination modify the charge transport in TTP derivatives. Our results show that the introduction of bromine substituents into TTP derivatives has a stronger effect than fluorination. The introduction of the fluorine atoms improves the hole transport in the l-TTP derivatives, while bromine atoms improve both hole and electron transport of the three TTP derivatives. Our findings suggest a new series of promising ambipolar organic materials.

The properties of the two dimensional quaternary compounds AgScP2Se6, AgBiP2Se6, CuBiP2Se6, and CuInP2S6 and the corresponding van der Waals heterostructures are studied using density functional theory. These compounds are dynamically stable, their electronic bandgaps range from 2.13 to 2.68 eV, and the positions of their band edges are suitable for their use for water splitting. Among the different heterostructures made from these monolayers, it is demonstrated that AgBiP2Se6/AgScP2Se6 and AgBiP2Se6/CuBiP2Se6 are type II heterostructures, which allow an efficient electron–hole separation. Then, we studied the electronic properties of the graphene/quaternary-2D-compound heterostructures: a shift of the graphene Dirac-point above the Fermi level is observed, which corresponds to a p-type heterostructure. Overall, this family of materials appears to be very promising for optical and electronic applications.

The effect of the electron-withdrawing fluorine, chlorine, and bromine atoms on the electronic and optical properties of crystalline tetrathienoanthracene and tetrathionoacridine derivatives were investigated by dispersion-corrected density functional theory. Our results also show that the position of sulfur atoms and the substitution of the CH group with a nitrogen atom can improve the charge transport of the title compounds. In addition, slight chemical modifications in the considered molecular derivatives makes smaller the molecular band gaps that facilitates the hole and electron injections. Also the halogenation substituents enhances the hole and the electron transport of the tetrathienoanthracene and tetrathionoacridine compounds. Based on our results, we propose a new set of promising hole and electron transport materials.

A statistical physics modelling analysis was performed to explain the adsorption of methylene blue (MB) dye on both nano-silica (RNS) and microwave modified nano–silica (MMNS) in the temperature range of 25–55 °C. Interestingly, it was demonstrated that the MB dye adsorption occurred via the formation of two layers on surfaces of both RNS and MMNS. The number of linked adsorbate (MB dye) molecules per functional groups varied from 0.59 to 1.0 for MB-RNS and from 0.64 to 1.112 for MB-MMNS, respectively. Based on these calculations, the adsorption orientation of MB molecules on these adsorbents was estimated to be a mixed orientation (parallel and non parallel) at tested temperatures. Overall, the occupied density of functional groups (Dm) at saturation was the parameter controlling the variation of the adsorption capacity. Calculated energies of MB dye adsorption mechanism indicated an exothermic process where physical forces were involved. These adsorbents showed a competitive performance compared to other materials used in dye removal.

In this paper, we propose a simple cluster model with limited basis sets to reproduce the unpaired electron distributions in a YTiO

International audience; The paper describes a joint refinement model of the spin-resolved one-electron reduced density matrix using simultaneously magnetic structure factors and magnetic directional Compton profiles. The model is guided by two strategies: (i) variation of basis functions and (ii) variation of the spin population matrix. The implementation for a finite system is based on an expansion of the natural orbitals on basis sets. To show the potential benefits brought by the joint refinement model, the paper also presents the refinement results using magnetic structure factors only. The joint refinement model provides very satisfactory results reproducing the pseudo-data. In particular, magnetic Compton profiles have a strong effect not only on the off-diagonal elements of the spin-resolved one-electron reduced density matrix but also on its diagonal elements.

The properties of Fe(1,10-phenanthroline)2(NCS)2 (Fe-phen) molecules deposited on Co/Cu(111) are studied with scanning tunneling microscopy (STM) operated in ultrahigh vacuum at low temperature (4 K) and ab initio calculations. Both the experimental and theoretical results are used to identify the high-spin (HS) state of Fe-phen. Additionally, the calculations reveal a strong spin-polarization of the density of states (DOS) and is validated experimentally using the spin sensitivity of spin-polarized STM. Finally, it is shown that the magnetic moment of the Fe-ion within HS Fe-phen is strongly magnetically coupled to the underlying magnetic Co through the NCS groups. These findings enable promising spintronic perspectives.