Electron Back-donation Research Articles

Methanation of carbon dioxide over ceria-praseodymia promoted Ni-alumina catalysts. Influence of metal loading, promoter composition and alumina modifier

Two series of ceria-praseodymia promoted Ni-alumina catalysts were prepared from two different commercial modified alumina supports (3.5 wt% SiO2-Al2O3 and 4.0 wt% La2O3-Al2O3) by the incipient wetness impregnation method in two successive steps. The resulting materials were characterized in terms of their physico-chemical properties by means of N2 physical adsorption at −196 °C, powder X-ray diffraction (XRD) and temperature programmed reduction with H2 (H2-TPR). Furthermore, the as-prepared catalysts were tested for the CO2 methanation reaction in a fixed-bed reactor at atmospheric pressure, gas hourly space velocity (GHSV) of 72,000 cm3·(h·gcat)−1 and CO2/H2 molar ratio of 1/4 over the temperature range from 25 up to 850 °C. The influence of the nominal Ni loading (3, 5 and 10 wt%), molar composition of the Ce/Pr mixed oxide promoter (80/20 and 60/40), and alumina modifier (silica and lanthana) on the catalytic performance was carefully analyzed. Among these three composition parameters, the alumina dopant and especially the Ni content appear to have by far a much more pronounced effect on both the CO2 conversion and CH4 selectivity as compared to the Ce/Pr mixed oxide composition. Specifically, from the catalytic tests the sample containing a 10 wt% Ni loading, a Ce/Pr mixed oxide promoter of 80/20 molar composition, and silica as modifier provides the highest catalytic activity in terms of CO2 conversion and CH4 selectivity. Such behaviour has been ascribed to a complex interplay between several factors, mainly the larger fraction of catalytically active β-type NiO species and the lesser concentration of strong basic sites on the catalyst surface, as well as the electron back donation effect from the surface Ni atoms to the adsorbed COx species, which favours the C–O bond cleavage (i.e., the rate-determining step of the methanation reaction). These findings are expected to be very helpful in order to rationally design synthetic strategies that allow developing highly active and low cost Ni-based catalysts for the CO2 methanation reaction.

Quantum chemical calculations, molecular dynamic (MD) simulations and experimental studies of using some azo dyes as corrosion inhibitors for iron. Part 2: Bis–azo dye derivatives

The adsorption behavior and inhibition mechanism of five synthesized bis-azo dye (BAD) derivatives on the corrosion of iron in aerated HNO3 and NaOH were investigated by performing potentiostatic polarization, weight loss (WL), thermometric and UV–visible spectra measurements. DFT calculations is applied to study the correlation between corrosion inhibition and global reactivity descriptors such as: EHOMO, ELUMO, molecular gap (ΔE), the dipole moment (μ), the global hardness (η), softness(S), electronegativity (χ), proton affinity (PA), electrophilicity (ω), nucleophilicity (ɛ), electrons transferred from inhibitors to metal surface (ΔN), initial molecule-metal interaction energy (Δψ), total electronic energy (E) and the energy change during electronic back-donation process (ΔEb-d). To mimic the real environment of corrosion inhibition, molecular dynamic (MD) simulations in aqueous phase have also been modelled consisting of all concerned species (inhibitor molecule, H2O, H3O+ ion, NO3− ion, OH− and Fe surface). The results confirmed that BAD molecules inhibit iron by adsorption behavior through donating and accepting electrons together with the formation of [Fe (II) and Fe (III)—BAD] chelate complex compounds. BAD's behavior is mainly chemisorption with some physisorption obeyed Frumkin and that of El-Awady adsorption isotherm. Kinetic parameters such as: (Kb, 1/y, Kads, f, ΔG°ads) have been determined and discussed. Binding energies of BAD molecules on Fe (110) surface followed the order: BAD_ 2 > BAD_ 1 > BAD_ 3 > BAD_ 4 > BAD_ 5. Theoretical results were found to be consistent with the experimental data reported. Our results provide important atomic/molecular insights into the anticorrosive mechanism of inhibitor molecules, which could help in understanding the organic-metal interface and designing more appropriate organic corrosion inhibitors.

Study of the Influence of the I-Based Electrolyte Composition on the Photoconversion Properties of p-Type Dye-Sensitized Solar Cells

In the framework of the research on dye-sensitized solar cells of p-type (p-DSCs) the definition and optimization of the electrolyte have been a crucial aspect for the reach of the recent records of photo-conversion for these devices. At the basis of this progress there was the replacement of the redox shuttle of reference I3−/I− with opportune redox mediators which deliver higher photocurrents and produce larger open circuit photovoltages. In the present study we intend to optimize the composition of the iodine-based electrolyte for p-DSCs employing variable concentrations of redox shuttle. Beside the general conditioning of the overall performance, the analysis of the influence of p-DSC electrolytes has concerned the aspects of the extent of optical parasitic absorption of the electrolyte, of the chemical aggressiveness of the redox species and of the control of the phenomena of electronic back-donation by the photoreduction product. Non-obvious correlations have been found between the main cell parameters (η, JSC, VOC, FF) and the electrolyte conductivity. In the present work, a photocurrent density higher than 4.0 mA*cm−2 is reported when I-based electrolyte (LiI 1.0 M and I2 1.0 M in ACN) was employed. EIS experiments proved that this outstanding photocurrent was due to the lowering of recombination phenomena.

Isonitrile-functionalized ruthenium nanoparticles: intraparticle charge delocalization through Ru=C=N interfacial bonds

Ruthenium nanoparticles (2.06 ± 0.46 nm in diameter) stabilized by 1-hexyl-4-isocyanobenzene (CNBH), denoted as RuCNBH, were prepared by the self-assembly of isonitrile molecules onto the surface of “bare” Ru colloids by virtue of the formation of Ru=C=N− interfacial bonds. FTIR measurements showed that the stretching vibration of the terminal −N≡C bonds at 2119 cm−1 for the monomeric ligands disappeared and concurrently three new bands at 2115, 2043, and 1944 cm−1 emerged with RuCNBH nanoparticles, which was ascribed to the transformation of −N≡C to Ru=C=N− by back donation of Ru-d electrons to the π* orbital of the organic ligands. Metathesis reaction of RuCNBH with vinyl derivatives further corroborated the nature of the Ru=C interfacial bonds. When 1-isocyanopyrene (CNPy) was bounded onto the Ru nanoparticles surface through Ru=C=N interfacial bond (denoted as RuCNPy), the emission maximum was found to red-shift by 27 nm, as compared to that of the CNPy monomers, along with a reduced fluorescence lifetime, due to intraparticle charge delocalization that arose from the conjugated Ru=C=N− interfacial bonds. The results of this study further underline the significance of metal−organic interfacial bonds in the control of intraparticle charge-transfer dynamics and the optical and electronic properties of metal nanoparticles.

DFT study of the interactions between thiophene-based corrosion inhibitors and an Fe4 cluster.

Understanding the physicochemical properties of corrosion inhibitors and their chemical interactions with metal surfaces is crucial to the design of improved (i.e., more efficient) corrosion inhibitors. In this work, the physicochemical properties of six thiophene-based corrosion inhibitors (2-acetylthiophene (AT), 2-formylthiophene (FT), thiophene (Th), 2-methyl-3-thiophenthiol (MTT), 2-pentylthiophene (PT), and 2-thenylthiol (TT)) were systematically studied by performing ab initio calculations at the MP2(full)/6-31G(2df,p) level of theory. Adsorption of the inhibitors on an iron surface was also modeled by investigating the interactions of these molecules with a tetrahedral Fe4 cluster using the B3LYP method and the 6-311G(d,p) basis set or the LanL2DZ basis set. The calculated results indicate that the nature of the substituent group present has a significant impact on the geometric and electronic structures of the thiophene-based molecules. The presence of an electron-donating group causes the electron density in the thiophene ring to increase, while the presence of an electron-withdrawing group has the opposite effect. Accordingly, the examined molecules were ranked in order of corrosion inhibition efficiency as follows: FT ≈ AT < Th<PT<TT<MTT. The calculated binding energies demonstrated that the π-1Fe and π-3Fe interaction configurations dominated over the S-1Fe configuration for all the compounds. Natural bond orbital analysis revealed that all of the thiophene-based compounds donate electrons from the π and σ orbitals of high-electron-density regions such as C2-S1-C5 and C3-C4 or from two lone pairs on S1 to the Fe4 cluster. Although electron donation from the thiophene-based compounds is always the dominant electron transfer process during adsorption, the backdonation of electrons from the 3d orbital of iron to σ*-antibonding orbitals of the thiophene compounds is also observed, especially in the case of π-3Fe parallel adsorption. Graphical abstract Optimized geometry, HOMO and LUMO for the π-3Fe interaction configuration of 2-pentylthiophene and Fe4 cluster.

Effects of phosphorus and alkyl substituents on C–H, C–C, and C–O bond rupture within carboxylic acids on Ru(0001)

Quantitative analysis of temperature programmed reaction (TPR) spectra of formic acid, acetic acid, propionic acid, and butyric acid decomposition on Ru(0001) and phosphorus (P)-modified Ru(0001) surfaces show that both the length of carboxylic acids alkyl substituents (i.e., R=H, CH3, CH2CH3, and CH2CH2CH3) and the presence of P atoms alter the intrinsic activation energy for bond rupture. Inversion analysis of TPR spectra reveal that the intrinsic activation energy barriers on Ru(0001) for C–H bond cleavage in formate is 94 kJ mol−1, while C–C bond cleavage (decarboxylation) barriers for acetate, propionate, and butyrate are 67, 49, and 55 kJ mol−1, respectively. The activation energies to decarboxylate all four of these species correlate linearly with differences between the homolytic dissociation energies of the relevant bonds (e.g., H-COOH, CH3-COOH, CH3CH2-COOH, and CH3CH2CH2-COOH), which suggests that longer alkyl substituents (e.g., propyl and butyl) stabilize bond rupture transition states by donating electron density to the R–COOH bond via inductive effects. Simultaneously, longer alkyl chains also promote self-stabilizing lateral interactions between carboxylates via van der Waals forces that increase the barriers for R–COOH bond rupture slightly (by ∼1–5 kJ mol−1) at high surface coverages. The addition of P atoms to Ru(0001) increases the intrinsic activation energies for the rupture of all bonds (i.e., C–O, C–H, and C–C bonds), specifically, by 5–50 kJ mol−1 for C–H and C–C bonds. P atoms change the Ru(0001) surface likely via an electronic effect by decreasing the extent of electron back donation from Ru atoms to the antibonding orbitals of the carboxylate intermediate. These results provide useful information for transition metal phosphide catalyst design and carboxylic acid alkyl substituent selection to tailor selectivity toward C–O, C–H, and C–C bond rupture.

Ambient Carbon Dioxide Capture Using Boron-Rich Porous Boron Nitride: A Theoretical Study.

The development of highly efficient sorbent materials for CO2 capture under ambient conditions is of great importance for reducing the impact of CO2 on the environment and climate change. In this account, strong CO2 adsorption on a boron antisite (BN) in boron-rich porous boron nitrides (p-BN) was developed and studied. The results indicated that the material achieved larger adsorption energies of 2.09 eV (201.66 kJ/mol, PBE-D). The electronic structure calculations suggested that the introduction of BN in p-BN induced defect electronic states in the energy gap region, which strongly impacted the adsorption properties of the material. The bonding between the BN defect and the CO2 molecule was clarified, and it was found that the electron donation first occurred from CO2 to the BN double-acceptor state then, followed by electron back-donation from BN to CO2 accompanied by the formation of a BN-C bond. The thermodynamic properties indicated that the adsorption of CO2 on the BN defect to form anionic CO2δ- species was spontaneous at temperatures below 350 K. Both the large adsorption energies and the thermodynamic properties ensured that p-BN with a BN defect could effectively capture CO2 under ambient conditions. Finally, to evaluate the energetic stability, the defect formation energies were estimated. The formation energy of the BN defects was found to strongly depend on the chemical environment, and the selection of different reactants (B or N sources) would achieve the goal of reducing the formation energy. These findings provided a useful guidance for the design and fabrication of a porous BN sorbent for CO2 capture.

Catalytic effects of calcium and potassium on a curved char surface in fuel reburning: A first-principles study on the adsorption of nitric oxide on single-wall carbon nanotubes with metal decoration

To investigate the role of a curved char surface in the nitric oxide (NO)-char reaction, single-wall carbon nanotubes (SWCNTs) were proposed as a model for simulating the curved char surface in first-principles calculations. The effect of calcium and potassium decoration on the adsorption of NO was compared for SWCNTs and graphene, the latter of which represented a flat char surface. The contribution of a curved surface to the NO-char reaction was insignificant in the absence of metals, as the binding energy of NO on pure SWCNTs was only 13% of that on pure graphene. In contrast, when calcium or potassium was present, NO adsorption on the curved surface became significant as the binding energies of NO on calcium- or potassium-decorated SWCNTs increased to 72% and 18% of those on the corresponding decorated graphene surfaces, respectively. The catalytic effect of calcium and potassium was attributed to electron transfer and backdonation between the 4s- and 3d-orbitals of the metal atoms and the NO molecule. Thus, the studies into NO adsorption on flat and curved char surfaces render it possible to determine the degree of catalytic effect of these two metals on the char surface during fuel reburning.

A computational study on corrosion inhibition performances of novel quinoline derivatives against the corrosion of iron

In this computational study, the adsorption and corrosion inhibition properties of some novel quinoline derivatives namely, 2-amino-7-hydroxy-4-phenyl-1,4-dihydroquinoline-3-carbonitrile (Q1), 2-amino-7-hydroxy-4-(p-tolyl)-1,4-dihydroquinoline-3-carbonitrile (Q2), 2-amino-7-hydroxy-4-(4-methoxyphenyl)-1,4-dihydroquinoline-3-carbonitrile) (Q3) and 2-amino-4-(4-(dimethylamino)phenyl)-7-hydroxy-1,4-dihydroquinoline-3-carbonitrile (Q4) on the corrosion of iron were investigated using quantum chemical and molecular dynamics simulation approaches. Quantum chemical calculations section of the study provides enough calculation and discussion on the relationship between corrosion inhibition and global reactivity descriptors such as EHOMO, ELUMO, HOMO-LUMO energy gap (ΔE), chemical hardness (η), softness (σ), electronegativity (χ), chemical potential (μ), electrophilicity (ω), nucleophilicity (ɛ), electrons transferred from inhibitors to metal surface (ΔN), initial molecule–metal interaction energy (Δψ), total electronic energy (E), the energy change during electronic back-donation process (ΔEb-d). The adsorption behaviors of studied compounds on Fe (110) surface were investigated with the help of molecular dynamics simulation approach. The binding energies calculated on Fe (110) surface of mentioned quinoline derivatives followed the order: Q4 > Q3 > Q2 > Q1. It should be noted that the results obtained in the study are in good agreement with experimental inhibition efficiency results earlier reported.

Increased Back-Bonding Explains Step-Edge Reactivity and Particle Size Effect for CO Activation on Ru Nanoparticles.

Carbon monoxide is a ubiquitous molecule, a key feedstock and intermediate in chemical processes. Its adsorption and activation, typically carried out on metallic nanoparticles (NPs), are strongly dependent on the particle size. In particular, small NPs, which in principle contain more corner and step-edge atoms, are surprisingly less reactive than larger ones. Hereby, first-principles calculations on explicit Ru NP models (1-2 nm) show that both small and large NPs can present step-edge sites (e.g., B5 and B6 sites). However, such sites display strong particle-size-dependent reactivity because of very subtle differences in local chemical bonding. State-of-the-art crystal orbital Hamilton population analysis allows a detailed molecular orbital picture of adsorbed CO on step-edges, which can be classified as flat (η1 coordination) and concave (η2 coordination) sites. Our analysis shows that the CO π-metal dπ hybrid band responsible for the electron back-donation is better represented by an oxygen lone pair on flat sites, whereas it is delocalized on both C and O atoms on concave sites, increasing the back-bonding on these sites compared to flat step-edges or low-index surface sites. The bonding analysis also rationalizes why CO cleavage is easier on step-edge sites of large NPs compared to small ones irrespective of the site geometry. The lower reactivity of small NPs is due to the smaller extent of the Ru-O interaction in the η2 adsorption mode, which destabilizes the η2 transition-state structure for CO direct cleavage. Our findings provide a molecular understanding of the reactivity of CO on NPs, which is consistent with the observed particle size effect.

Matrix isolation infrared spectroscopic study of 4-Pyridinecarboxaldehyde and of its UV-induced photochemistry

The structure, infrared spectrum, barrier to internal rotation, and photochemistry of 4-pyridinecarboxaldehyde (4PCA) were studied by low-temperature (10K) matrix isolation infrared spectroscopy and quantum chemical calculations undertaken at both Moller-Plesset to second order (MP2) and density functional theory (DFT/B3LYP) levels of approximation. The molecule has a planar structure (Cs point group), with MP2/6-311++G(d,p) predicted internal rotation barrier of 26.6kJmol−1, which is slightly smaller than that of benzaldehyde (~30kJmol−1), thus indicating a less important electron charge delocalization from the aromatic ring to the aldehyde moiety in 4PCA than in benzaldehyde. A complete assignment of the infrared spectrum of 4PCA isolated in an argon matrix has been done for the whole 4000–400cm−1 spectral range, improving over previously reported data. Both the geometric parameters and vibrational frequencies of the aldehyde group reveal the relevance in this molecule of the electronic charge back-donation effect from the oxygen trans lone electron pair to the aldehyde CH anti-bonding orbital. Upon in situ UV irradiation of the matrix-isolated compound, prompt decarbonylation was observed, leading to formation of pyridine.

Influence of Carbon Support on Electronic Structure and Catalytic Activity of Pt Catalysts: Binding to the CO Molecule

Single-atom catalysts, especially with single Pt atoms, exhibit potentially improved catalytic activity as compared to metal clusters and metal surfaces. Here, the atop and bridged bondings of the CO molecule on the Pt/C system are studied. Vibrational frequencies, Mulliken populations, charge transfer, charge density differences, and density of states are examined to determine the influence of the carbon support on electronic properties and catalytic activity of the Pt adatom and dimer. Comparing orbital populations and the amount of electron transfer to/from the CO molecule shows that the net amount of electron transfer to the antibonding 2π* orbitals of the CO molecule is higher for the supported Pt dimer than for the substrate-free Pt dimer, which leads to a lower vibrational frequency and a larger C–O bond distance. The hybridization between the π orbitals of the polycyclic aromatic hydrocarbons surface and the d orbitals of the Pt adatoms is responsible for enhancing the back-donation of electrons t...

Theoretical survey on M@C80 (M = Ca, Sr, and Ba): Behavior of different alkaline earth metal impacting the chemical stability and electronic properties

Structures of mono-metallofullerenes M@C80 (M=Ca, Sr, and Ba) that separated in early experiment are determined owning the C2v(31920)-C80 cage. The change rule of properties for M@C80 (M=Ca, Sr, and Ba) influenced by different inner metal are discussed. As the trapped metal changes from calcium to barium, performance of thermodynamic stabilities for M@C2v(31920)-C80, M@C2v(31922)-C80, and M@D5h(31923)-C80 are significantly different. Orbital analysis suggests that the lowest unoccupied molecular orbitals (LUMOs) of Ca@C2v(31920)-C80 and Ca@D5h(31923)-C80 are mostly located on the trapped metal, whereas reduction reactions of Ca@C2v(31920)-C80 and Ca@D5h(31923)-C80 occur on the fullerene cage. Natural electron configuration analyses demonstrates that the decentralized electron back-donation of Ba@C2v(31920)-C80 would take responsible for the instability of itself. Electronic properties such as electron affinities and ionization potentials are significantly affected by encapsulated metal are also found. Computational UV–visible–NIR spectra for M@C2v(31920)-C80 (M=Ca, Sr, Ba) are in perfect accord with the spectra obtained experimentally.

On the nature of chemical bonding in the all-metal aromatic [Sb3Au3Sb3](3-) sandwich complex.

In a recent communication, an all-metal aromatic sandwich [Sb3Au3Sb3](3-) was synthesized and characterized. We report herein a density-functional theory (DFT) study on the chemical bonding of this unique cluster, which makes use of a number of computational tools, including the canonical molecular orbital (CMO), adaptive natural density partitioning (AdNDP), Wiberg bond index, and orbital composition analyses. The 24-electron, triangular prismatic sandwich is intrinsically electron-deficient, being held together via six Sb-Sb, three Au-Au, and six Sb-Au links. A standard, qualitative bonding analysis suggests that all CMOs are primarily located on the three Sb3/Au3/Sb3 layers, three Au 6s based CMOs are fully occupied, and the three extra charges are equally shared by the two cyclo-Sb3 ligands. This bonding picture is referred to as the zeroth order model, in which the cluster can be formally formulated as [Sb3(1.5+)Au3(3-)Sb3(1.5+)](3-) or [Sb3(0)Au3(3-)Sb3(0)]. However, the system is far more complex and covalent than the above picture. Seventeen CMOs out of 33 in total involve remarkable Sb → Au electron donation and Sb ← Au back-donation, which are characteristic of covalent bonding and effectively redistribute electrons from the Sb3 and Au3 layers to the interlayer edges. This effect collectively leads to three Sb-Au-Sb three-center two-electron (3c-2e) σ bonds as revealed in the AdNDP analyses, despite the fact that not a single such bond can be identified from the CMOs. Orbital composition analyses for the 17 CMOs allow a quantitative understanding of how electron donation and back-donation redistribute the charges within the system from the formal Sb3(0)/Au3(3-) charge states in the zeroth order model to the effective Sb3(1.5-)/Au3(0) charge states, the latter being revealed from the natural bond orbital analysis.

Exo-bonded six-membered heterocycle in the crystal structures of RE7Co2Ge4 (RE = La-Nd).

In this article four new ternary phases of RE7Co2Ge4 (RE = La-Nd) are reported. They were synthesized by a solid-state reaction of the elements at high temperature, and their crystal structures were investigated by single crystal X-ray diffraction data. The isostructural phases crystallize in a new monoclinic structure type, space group P21/c, Z = 4, Pearson code mP52, and Wyckoff sequence e13. They feature planar {Co4Ge6} clusters consisting of a benzene-like six-membered (Co4Ge2) metal heterocycle and four Co-Ge exo-bonds. Band structure calculations were carried out to investigate the electronic structures of La7Co2Ge4, in order to understand the nature of the chemical bonding, and the structure directing factors that determine the atomic ordering and the structure stability. These calculations indicate that the cobalt mid-transition metals are present as (formally) anionic species. They also reveal significant valence electron back-donation from the anionic {Co4Ge6} units to the La-d orbitals through multicenter bonding involving all atoms of the structure, which is key for the structure's stability with respect to incomplete charge transfer. The applicability of the 18 - n rule in rationalizing the Co-Co relative bond strength was also assessed and, the impact of these metal-metal interactions in stabilizing these clusters was described. Similar valence electron back-donation to stabilize further unusual cluster shapes is expected in other rare earth-transition metal-main group phases.

Structure and Bonding of an Intergrowth Phase Ca7Ag2+xGe7–x (x ≈ 2/3) Featuring a Zintl‐Type Polyanionic Chain

AbstractSingle crystals of a new ternary phase, Ca7Ag2+xGe7–x [x = 0.48(3)], were obtained from as side‐product of high‐temperature solid‐state reactions, and its crystal structure determined by X‐ray diffraction methods. Following the Zintl concept, the anionic substructure consists of a novel pentameric Zintl anion [Ge5]12– with C2v local symmetry, as well as [AgxGe2–x](6–3x)– units accounting for [Ge2]6– dimers and isolated Ge4– (and Ag+) species sharing the same atomic sites. DFT‐level band structure calculations were carried out on a hypothetical, fully ordered model (x = 0). We found that the electronic structure associated with the planar W‐shaped [Ge5]12– polyanions is more suited to optimize the structure's stability than the helical configuration of the isoelectronic [Se5]2–, in the context of incomplete charge transfer from the electropositive metal Ca. Thus, the antibonding states at the Fermi level that are centered on the two [Gen](2n+2)– oligomers can be depopulated by means of Ge‐to‐Ca electron back donation, strengthening at the same time the Ge–Ge bonds. These antibonding states also endow the system with substantial electronic flexibility, which may result in some phase width. Finally, plausible local ordering models of Ag/Ge mixing in [AgxGe2–x](6–3x)– units for x = 2/3, as expected from the Zintl concept, are briefly discussed within the “coloring problem” approach.

DFT Study of a Novel Organic Film: The Structural versus Magnetic Effects

Unsaturated fatty acids have great interest by their activities as industrial materials in novel applications. In the present work, the cis-3-hexenoic acid (HA) adsorbed on the Ni(111) surface was studied by first-principles calculations using the Vienna Ab Initio Simulation Package (VASP). The most stable location for HA is presented on top site of Ni(111), although the energies are very similar for all the adsorption sites. The surface-molecule interaction takes place between the carboxyl group of HA and surrounding Ni atoms. The adsorption is weak and consequently the metal-molecule length is enhanced. The carboxyl group is elongated and weakened after adsorption giving rise to a shift in stretching frequencies. There are notable changes on the magnetic moments values of Ni surface atoms neighboring to the molecule that mainly induced magnetic moments on O and H atoms. Noticeable charge transfer occurs in 3d 4s, p Ni orbitals and 2s C, 2s p O, 1s H orbitals of carboxyl group. The surface presents positive work function changes after adsorption as a consequence of an electron back-donation. During interaction, the significance of the magnetic effects over the structural effects is evidenced. This sets the stage for a future adsorption process improvement based on the modification of the surface magnetic properties.

The Triple‐Bond Metathesis of Aryldiazonium Salts: A Prospect for Dinitrogen Cleavage

AbstractThe {N2} unit of aryldiazonium salts undergoes unusually facile triple‐bond metathesis on treatment with molybdenum or tungsten alkylidyne ate complexes endowed with triphenylsilanolate ligands. The reaction transforms the alkylidyne unit into a nitrile and the aryldiazonium entity into an imido ligand on the metal center, as unambiguously confirmed by X‐ray structure analysis of two representative examples. A tungsten nitride ate complex is shown to react analogously. Since the bonding situation of an aryldiazonium salt is similar to that of metal complexes with end‐on‐bound dinitrogen, in which {N2}→M σ donation is dominant and electron back donation minimal, the metathesis described herein is thought to be a conceptually novel strategy toward dinitrogen cleavage devoid of any redox steps and, therefore, orthogonal to the established methods.

The Triple-Bond Metathesis of Aryldiazonium Salts: A Prospect for Dinitrogen Cleavage.

The {N2 } unit of aryldiazonium salts undergoes unusually facile triple-bond metathesis on treatment with molybdenum or tungsten alkylidyne ate complexes endowed with triphenylsilanolate ligands. The reaction transforms the alkylidyne unit into a nitrile and the aryldiazonium entity into an imido ligand on the metal center, as unambiguously confirmed by X-ray structure analysis of two representative examples. A tungsten nitride ate complex is shown to react analogously. Since the bonding situation of an aryldiazonium salt is similar to that of metal complexes with end-on-bound dinitrogen, in which {N2 }→M σ donation is dominant and electron back donation minimal, the metathesis described herein is thought to be a conceptually novel strategy toward dinitrogen cleavage devoid of any redox steps and, therefore, orthogonal to the established methods.

Adsorption states of typical intermediates on Ag/Al2O3 catalyst employed in the selective catalytic reduction of NOx by ethanol

The adsorption of ethanol and important intermediates onto Ag/Al2O3 catalyst employed in the selective catalytic reduction of NOx by ethanol was simulated by density functional theory. Considering the interaction between Ag metal and Al2O3 support, typical Ag–O–Al entities, i.e., Ag–O–Altetra and Ag–O–Alocta, (tetra = tetrahedral and octa = octahedral refer to the coordination sites of Al), were selected as potential adsorption sites on the surface of the catalyst. Ethanol, and enolic and isocyanate species were preferentially adsorbed and activated by Ag–O–Altetra entities rather than by Ag–O–Alocta entities. The strong Lewis acidity of Altetra in the Ag–O–Altetra entity was very important, enabling the entity to accept an electron via forward donation from either the C–O σ bond in ethanol or the N–C σ bond in the –NCO species. Moreover, the hybridization of the Ag and Al orbitals was critical for electron back donation from the Ag–O–Altetra entity to the C–C π bond in the enolic species or N–C π bond in the –NCO species. The significant activation of the N–C bond in –NCO on the Ag–O–Altetra sites facilitated cleavage of –NCO to form N2. Thus, we can conclude that the acidity of the Al site and the interaction between Ag and Al play key roles in the selective catalytic reduction of NOx by ethanol over Ag/Al2O3.