Magneli-Phases in Anatase Strongly Promote Co-Catalyst-Free Photocatalytic Hydrogen Evolution

Magneli phases of titanium dioxide (such as Ti4O7, Ti5O9, etc.) provide electronic properties, namely a stable metallic behavior at room temperature. In this manuscript, we demonstrate that nanoscopic Magneli phases, formed intrinsically in anatase during a thermal aerosol synthesis, can enable significant photocatalytic H2 generation. This without the use of any extrinsic co-catalyst in anatase. Under optimized conditions, mixed phase particles of 30 percent anatase, 25 percent Ti4O7 and 20 percent Ti5O9 are obtained that can provide, under solar light, direct photocatalytic H2 evolution at a rate of 145 micromol h-1 g-1. These anatase particles contain 5-10 nm size inter-grown phases of Ti4O7 and Ti5O9. Key is the metallic band of Ti4O7 that induces a particle internal charge separation and transfer cascade with suitable energetics and favorable dimensions that are highly effective for H2 generation

1,2-CH Bond Activation of Pyridine across a Transient Titanium Alkylidene Radical and Re-Formation of the TiCH^tBu Moiety

Reduction of the titanium alkylidene [(PNP)­TiCH^<i>t</i>Bu­(OTf)] (PNP^– = N­[2-P^<i>i</i>Pr₂-4-methylphenyl]₂^–) with KC₈ in the presence of pyridine results in formation of the transient titanium­(III) alkylidene radical [(PNP)­TiCH^<i>t</i>Bu)] (<b>A</b>) or the adduct [(PNP)­TiCH^<i>t</i>Bu)­(NC₅H₅)] (<b>B</b>), which activates the C–H bond of pyridine to form the titanium­(III) pyridyl alkyl complex [(PNP)­Ti­(CH₂^<i>t</i>Bu)­(η²-NC₅H₄)] (<b>1</b>) in 64% yield as brown microcrystals. Low-temperature X-band EPR spectroscopy and single-crystal X-ray diffraction studies confirm the identity of <b>1</b> as a d¹ metal-centric radical with superhyperfine coupling to one nitrogen atom and having a side-on pyridyl moiety, which results in formation of the two isomeric forms <b>1a</b>,<b>b</b>. Oxidation of <b>1</b> with [FeCp*₂]­[OTf] cleanly promotes α-hydrogen abstraction to re-form [(PNP)­TiCH^<i>t</i>Bu­(OTf)] with concurrent elimination of pyridine and FeCp*₂. Re-formation of the alkylidene moiety most likely stems from an intermediate such as [(PNP)­Ti­(CH₂^<i>t</i>Bu)­(η²-NC₅H₄)­(OTf)] (<b>C</b>)

Exploring Oxidation State-Dependent Selectivity in Polymerization of Cyclic Esters and Carbonates with Zinc(II) Complexes

Summary: Neutral zinc alkoxide complexes show high activity toward the ring-opening polymerization of cyclic esters and carbonates, to generate biodegradable plastics applicable in several areas. Herein, we use a ferrocene-chelating heteroscorpionate complex in redox-switchable polymerization reactions, and we show that it is a moderately active catalyst for the ring-opening polymerization of L-lactide, ɛ-caprolactone, trimethylene carbonate, and δ-valerolactone. Uniquely for this type of catalyst, the oxidized complex has a similar polymerization activity as the corresponding reduced compound, but displays significantly different rates of reaction in the case of trimethylene carbonate and δ-valerolactone. Investigations of the oxidized compound suggest the presence of an organic radical rather than an Fe(III) complex. Electronic structure and density functional theory (DFT) calculations were performed to support the proposed electronic states of the catalytic complex and to help explain the observed reactivity differences. The catalyst was also compared with a monomeric phenoxide complex to show the influence of the phosphine-zinc interaction on catalytic properties. : Chemistry; Inorganic Chemistry; Catalysis; Polymer Chemistry Subject Areas: Chemistry, Inorganic Chemistry, Catalysis, Polymer Chemistr

From an Fe2P3 complex to FeP nanoparticles as efficient electrocatalysts for water-splitting

In large-scale, hydrogen production from water-splitting represents the most promising solution for a clean, recyclable, and low-cost energy source. The realization of viable technological solutions requires suitable efficient electrochemical catalysts with low overpotentials and long-term stability for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) based on cheap and nontoxic materials. Herein, we present a unique molecular approach to monodispersed, ultra-small, and superiorly active iron phosphide (FeP) electrocatalysts for bifunctional OER, HER, and overall water-splitting. They result from transformation of a molecular iron phosphide precursor, containing a [Fe2P3] core with mixed-valence FeIIFeIII sites bridged by an asymmetric cyclo-P(2+1)3− ligand. The as-synthesized FeP nanoparticles act as long-lasting electrocatalysts for OER and HER with low overpotential and high current densities that render them one of the best-performing electrocatalysts hitherto known. The fabricated alkaline electrolyzer delivered low cell voltage with durability over weeks, representing an attractive catalyst for large-scale water-splitting technologies

Fundamental aspects of H \u3c inf\u3e 2 S adsorption on CPO-27-Ni

Adsorption of H2S on the Ni2(dhtp)(H 2O)2·8H2O metal-organic framework (known as CPO-27-Ni or MOF-74-Ni) is characterized by in situ powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR), Raman, and UV-visible spectroscopy) and by first-principles periodic boundary conditions calculations. PXRD results show very high stability of CPO-27-Ni framework in the presence of H 2S. Nevertheless, as evidenced by change in color of the sample from pale yellow to dark green, the adsorption of H2S strongly affects the coordination of Ni sites. FTIR results show the reversible molecular adsorption of H2S. Experimental and computed energies of interaction reveal good agreement. Quantitative data considering energetic aspects (calorimetric measurements) are also included. This work highlights the fundamentals of H 2S adsorption onto the CPO-27-Ni framework. © 2013 American Chemical Society