A systematic DFT study of structure and electronic properties of titanium dioxide.

DFT functionals are of paramount importance for an accurate electronic and structural description of transition metal systems. In this work, a systematic analysis using some well-known and commonly used DFT functionals is performed. A comparison of the structural and energetic parameters calculated with the available experimental data is made in order to find the adequate functional for an accurate description of the TiO bulk and surface of both anatase and rutile structures.

Operando Mobile Catalysis for Reverse Water Gas Shift Reaction.

Metal atoms on the support serve as active sites for many heterogeneous catalysts. However, the active metal sites on the support are conventionally described as static, and the intermediates adsorbed on the support far away from the active metal sites cannot be transformed. Herein, we report the first example of operando mobile catalysis to promote catalytic efficiency by enhancing the collision probability between active sites and reactants or reaction intermediates.

Lithium Promotes Acetylide Formation on MgO During Methane Coupling Under Non-Oxidative Conditions.

A prototypical material for the oxidative coupling of methane (OCM) is Li/MgO, for which Li is known to be essential as a dopant to obtain high C selectivities. Herein, Li/MgO is demonstrated to be an effective catalyst for non-oxidative coupling of methane (NOCM). Moreover, the presence of Li is shown to favor the formation of magnesium acetylide (MgC ), while pure MgO promotes coke formation as evidenced by solid-state C NMR, thus indicating that Li promotes C-C bond formation.

Role and dynamics of transition metal carbides in methane coupling.

Transition metal carbides have numerous applications and are known to excel in terms of hardness, thermal stability and conductivity. In particular, the Pt-like behavior of Mo and W carbides has led to the popularization of metal carbides in catalysis, ranging from electrochemically-driven reactions to thermal methane coupling. Herein, we show the active participation of carbidic carbon in the formation of C products during methane coupling at high temperature that is associated with the dynamics of Mo and W carbides.

Non-oxidative Methane Coupling over Silica versus Silica-Supported Iron(II) Single Sites.

Non-oxidative CH coupling is promoted by silica with incorporated iron sites, but the role of these sites and their speciation under reaction conditions are poorly understood. Here, silica-supported iron(II) single sites, prepared via surface organometallic chemistry and stable at 1020 °C in vacuum, are shown to rapidly initiate CH coupling at 1000 °C, leading to 15-22 % hydrocarbons selectivity at 3-4 % conversion. During this process, iron reduces and forms carburized iron(0) nanoparticles.

Correction: Understanding of binding energy calibration in XPS of lanthanum oxide by in situ treatment.

Correction for 'Understanding of binding energy calibration in XPS of lanthanum oxide by in situ treatment' by Jerry Pui Ho Li et al., Phys. Chem.

Understanding of binding energy calibration in XPS of lanthanum oxide by in situ treatment.

Rare earth oxides have seen increased usage over the years in batteries and catalysts. Due to their unique electronic properties, they are the subject of fundamental and practical interest. However, the complexity in their electronic structures makes unambiguous characterization, such as X-ray photoelectron spectroscopy (XPS), very challenging.

Monomeric Copper(II) Sites Supported on Alumina Selectively Convert Methane to Methanol.

Monomeric Cu sites supported on alumina, prepared using surface organometallic chemistry, convert CH to CH OH selectively. This reaction takes place by formation of CH O surface species with the concomitant reduction of two monomeric Cu sites to Cu , according to mass balance analysis, infrared, solid-state nuclear magnetic resonance, X-ray absorption, and electron paramagnetic resonance spectroscopy studies. This material contains a significant fraction of Cu active sites (22 %) and displays a selectivity for CH OH exceeding 83 %, based on the number of electrons involved in the transformation.

Evaluation of Thin-Layer Chromatography-Laser Desorption Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometric Imaging for Visualization of Crude Oil Interactions.

A light oil was separated into four chromatographic fractions that serve as proxy for SARA fractions. The fractions were (semi)quantified on a rod by TLC-flame ionization detection and characterized on a plate with laser desorption ionization-mass spectrometry imaging (TLC-LDI-MS). Comparisons of (semi)quantitative TLC-FID and qualitative TLC-LDI-MS results showed that LDI-MS was most sensitive for detection of molecules in the polar P1 fraction, and, to some extent, for the aromatics fraction, while no signal was observed for the most polar P2 and saturates fractions.

Capturing the Genesis of an Active Fischer-Tropsch Synthesis Catalyst with Operando X-ray Nanospectroscopy.

A state-of-the-art operando spectroscopic technique is applied to Co/TiO catalysts, which account for nearly half of the world's transportation fuels produced by Fischer-Tropsch catalysis. This allows determination of, at a spatial resolution of approximately 50 nm, the interdependence of formed hydrocarbon species in the inorganic catalyst. Observed trends show intra- and interparticular heterogeneities previously believed not to occur in particles under 200 μm.

Shape and Size of Cobalt Nanoislands Formed Spontaneously on Cobalt Terraces during Fischer-Tropsch Synthesis.

Cobalt-based catalysts undergo a massive and spontaneous reconstruction to form uniform triangular nanoislands under Fischer-Tropsch (FT) conditions. This reconstruction is driven by the unusual and synergistic adsorption of square-planar carbon and CO at the 4-fold edge sites of the nanoislands, driving the formation of triangular islands. The size of the nanoislands is determined by the balance between energy gain from creating C/CO-covered edges and energy penalty to create C/CO-covered corners.

Direct evidence of water-assisted sintering of cobalt on carbon nanofiber catalysts during simulated Fischer-Tropsch conditions revealed with in situ mossbauer spectroscopy.

Cobalt on carbon nanofiber model catalysts with very small dispersed cobalt particles of 5 nm were subjected to H(2)O/H(2) treatments at 20 bar and 220 degrees C. Using in situ Mossbauer spectroscopy we could unambiguously prove that oxidation of the nanoparticles by water will not occur when hydrogen is present. Only in a water/argon atmosphere did oxidation take place.