A review on transition metal oxides in catalysis.

Transition Metal Oxides (TMOs) have drawn significant attention due to their diverse range of properties and applications. The partially filled d orbitals of the transition metal ions, with highly electronegative oxygen atoms, give rise to unique electronic structures that lead to multiple applications due to their magnetic, optical, and structural properties. These properties have a direct influence on chemical reactions that enable tailoring materials for specific applications in catalysis, such as electrocatalysis and photocatalysis. While the potential of TMOs is promising, their development for enhanced functional properties poses numerous challenges. Among these challenges, identifying the appropriate synthesis processes and employing optimal characterization techniques are crucial. In this comprehensive review, an overview of recent trends and challenges in the synthesis and characterization of highly functional TMOs as well as ceramics will be covered with emphasis on catalytic applications. Mesoporous materials play a key role in augmenting their functionality for various applications and will be covered. Ab-initio modeling aspects for the design and development of novel TMO will be also discussed.

Arsenate Anion-π Interactions on Amine-Modified Polydivinylbenzene in Aqueous Systems: Experimental and Theoretical Investigation.

Anion-π interactions aiding in the adsorption of anions in the solution phase, though challenging to quantify, have attracted a lot of attention in supramolecular chemistry. We present the design of a polymer adsorbent that quantifies the adsorption of arsenate ions experimentally by optimizing anion-π interactions in a purely aqueous system and use density functional theory to compare these results with theoretical data. Arsenate anions are removed from water by amine-functionalized polydivinylbenzene using the comonomer 1-vinyl-1,2,4-triazole, which was cross-linked with divinylbenzene via radical polymerization in a hydrothermal procedure. The amine-functionalized polydivinylbenzene successfully removed arsenate anions from water with a capacity of 46 mg g-1, a 70% increase compared to the nonfunctionalized polydivinylbenzene (27 mg g-1) capacity under the same conditions. Adsorption is best described by the Sips isotherm model with a correlation coefficient R2 factor of 0.99, indicating that adsorption sites are homogeneous, and adsorption occurred by forming a monolayer. Kinetic studies indicated that adsorption is second order in the amine-functionalized polydivinylbenzene. Computational studies using density functional theory showed that the 1-vinyl-1,2,4-triazole comonomer improved the thermodynamic stability of the anionic-π interactions of polydivinylbenzene with arsenate anions. Electrostatic interactions dominate the mechanism of adsorption in polydivinylbenzene compared to the anion-induced interactions that dominate adsorption in amine-functionalized polydivinylbenzene.

Magnetically Doped Molybdenum Disulfide Layers for Enhanced Carbon Dioxide Capture.

Carbon capture and storage (CCS) technologies have the potential for reducing greenhouse gas emissions and creating clean energy solutions. One of the major aspects of the CCS technology is designing energy-efficient adsorbent materials for carbon dioxide capture. In this research, using a combination of first-principles theory, synthesis, and property measurements, we explore the CO2 gas adsorption capacity of MoS2 sheets via doping with iron, cobalt, and nickel. We show that substitutional dopants act as active sites for CO2 adsorption. The adsorption performance is determined to be dependent on the type of dopant species as well as its concentration. Nickel-doped MoS2 is found to be the best adsorbent for carbon capture with a relatively high gas adsorption capacity compared to pure MoS2 and iron- and cobalt-doped MoS2. Specifically, Brunauer-Emmett-Teller (BET) measurements show that 8 atom % Ni-MoS2 has the highest surface area (51 m2/g), indicating the highest CO2 uptake relative to the other concentrations and other dopants. Furthermore, we report that doping could lead to different magnetic solutions with changing electronic structures where narrow band gaps and the semimetallic tendency of the substrate are observed and can have an influence on the CO2 adsorption ability of MoS2. Our results provide a key strategy to the characteristic tendencies for designing highly active and optimized MoS2-based adsorbent materials utilizing the least volume of catalysts for CO2 capture and conversion.

Surface structure and energetics of low index facets of bismuth ferrite.

Bismuth ferrite (BiFeO3) is a multiferroic material that has received significant interest due to its functional properties which could lead to potential novel applications in microelectronics, spintronics, and controlled catalytic reactions. Here, we provide the results of an extensive theoretical study to understand the surface structure and describe the energetics of differently terminated BiFeO3 surfaces. We specifically evaluate low index crystal facets and surface level atomic terminations via density functional theory and ab initio thermodynamics techniques. Our findings indicate that surface stability with varying terminations is strongly dependent on the oxygen partial pressure and chemical potentials of bismuth and iron. In oxygen rich environments, the results suggest that (100)-O and (110)-O and terminated surfaces are more stable compared to other surface terminations and facets. On the other hand, in a relatively oxygen poor environments, we observe that (110)-Bi and (110)-Fe are more stable. The calculations also show that the majority of BFO surfaces exhibit metallic behavior with the exception of the O-terminated (100) and (110) surfaces.

Mesoporous Iron Sulfide for Highly Efficient Electrocatalytic Hydrogen Evolution.

We report a facile synthetic protocol to prepare mesoporous FeS2 without the aid of hard template as an electrocatalyst for the hydrogen evolution reaction (HER). The mesoporous FeS2 materials with high surface area were successfully prepared by a sol-gel method following a sulfurization treatment in an H2S atmosphere. A remarkable HER catalytic performance was achieved with a low overpotential of 96 mV at a current density of 10 mA·cm-2 and a Tafel slope of 78 mV per decade under alkaline conditions (pH 13). The theoretical calculations indicate that the excellent catalytic activity of mesoporous FeS2 is attributed to the exposed (210) facets. The mesoporous FeS2 material might be a promising alternative to the Pt-based electrocatalysts for water splitting.

Ni9Te6(PEt3)8C60 Is a Superatomic Superalkali Superparamagnetic Cluster Assembled Material (S(3)-CAM).

First-principles theoretical studies enable an electronic and magnetic characterization of the recently synthesized Ni9Te6(PEt3)8C60 ionic material consisting of Ni9Te6(PEt3)8 superatoms and C60. The PEt3 ligands are shown to create an internal coulomb well that lifts the quantum states of the Ni9Te6 cluster, lowering its ionization potential to 3.39 eV thus creating a superalkali motif. The metallic core has a spin magnetic moment of 5.3 µB in agreement with experiment. The clusters are marked by low magnetic anisotropy energy (MAE) of 2.72 meV and a larger intra-exchange coupling exceeding 0.2 eV, indicating that the observed paramagnetic behavior around 10K is due to superparamagnetic relaxations. The magnetic motifs separated by C60 experience a weak superexchange that stabilizes a ferromagnetic ground state as observed around 2 K. The calculated MAE is sensitive to the charged state that could account for the observed change in magnetic transition temperature with size of the ligands or anion.

Conceptual Basis for Understanding C-C Bond Activation in Ethane by Second Row Transition Metal Carbides.

It has been suggested that the addition of carbon to Mo and W may improve their catalytic properties and even grant these metal carbides behaviors similar to those of late transition metals such as Pd and Pt. First-principles studies on the C-C bond activation of ethane by 4d transition metal (TM) atoms and TMC molecules have been carried out to develop a conceptual model underlying the changes. We find that the addition of carbon to TM atoms leads to large variations in the activation barrier depending on the metal, and that MoC indeed reveals a pronounced reduction in the C-C bond activation energy. A critical examination of molecular orbitals shows that the changes in reactivity are not linked to a dramatic increase in the filling of 4d states as implied by the analogy with Pd. The reactivity is governed by the location and filling of the 5s and 4d orbitals, with the different orbitals controlling different facets of reactivity. The 5s state controls the initial binding of ethane, with a strong anticorrelation between the ethane binding energy and the 5s occupation, while the location of the 4dz(2) orbital controls the reaction barrier that controls the activation energy for cleaving the C-C bond.

First-principles studies on graphene-supported transition metal clusters.

Theoretical studies on the structure, stability, and magnetic properties of icosahedral TM13 (TM = Fe, Co, Ni) clusters, deposited on pristine (defect free) and defective graphene sheet as well as graphene flakes, have been carried out within a gradient corrected density functional framework. The defects considered in our study include a carbon vacancy for the graphene sheet and a five-membered and a seven-membered ring structures for graphene flakes (finite graphene chunks). It is observed that the presence of defect in the substrate has a profound influence on the electronic structure and magnetic properties of graphene-transition metal complexes, thereby increasing the binding strength of the TM cluster on to the graphene substrate. Among TM13 clusters, Co13 is absorbed relatively more strongly on pristine and defective graphene as compared to Fe13 and Ni13 clusters. The adsorbed clusters show reduced magnetic moment compared to the free clusters.