Direct Photocatalytic Synthesis of Acetic Acid from Methane and CO at Ambient Temperature Using Water as Oxidant.

Direct functionalization of methane selectively to value-added chemicals is still one of the main challenges in modern science. Acetic acid is an important industrial chemical produced nowadays by expensive and environmentally unfriendly carbonylation of methanol using homogeneous catalysts. Here, we report a new photocatalytic reaction route to synthesize acetic acid from CH4 and CO at room temperature using water as the sole external oxygen source. The optimized photocatalyst consists of a TiO2 support and ammonium phosphotungstic polyoxometalate (NPW) clusters anchored with isolated Pt single atoms (Pt1). It enables a stable synthesis of 5.7 mmol·L-1 acetic acid solution in 60 h with the selectivity over 90% and 66% to acetic acid on liquid-phase and carbon basis, respectively, with the production of 99 mol of acetic acid per mol of Pt. Combined isotopic and in situ spectroscopy investigation suggests that synthesis of acetic acid proceeds via a photocatalytic oxidative carbonylation of methane over the Pt1 sites, with the methane activation facilitated by water-derived hydroxyl radicals.

Correction: Fast prediction of oxygen reduction reaction activity on carbon nanotubes with a localized geometric descriptor.

Correction for 'Fast prediction of oxygen reduction reaction activity on carbon nanotubes with a localized geometric descriptor' by Kunran Yang et al., Phys. Chem. Chem. Phys., 2020, 22, 890-895, DOI: 10.1039/C9CP04885E.

Fast prediction of oxygen reduction reaction activity on carbon nanotubes with a localized geometric descriptor.

The oxygen reduction reaction (ORR) is a process of primary importance in fuel cell technology. The efficiency of carbon-based materials in this field has been already confirmed by many experimental studies, especially when doped with nitrogen or boron. In this work, we propose a localized geometric descriptor, based on the pyramidalization angle to report ORR activity on carbon nanotubes (CNTs). Our descriptor reflects the local curvature of the surface and the torsion of the π orbital system. We showed that the surface reactivity is directly related to the pyramidalization angle at the active sites. Nitrogen and boron doping makes it possible to reach a low overpotential for weakly curved surfaces, whereas for undoped surfaces the ideal ORR activity is only reached for highly curved CNTs. Consequently, the optimal size of the nanotube is determined by the doping type. Hence, we demonstrated a high statistical quality correlation between the adsorption energies of surface species and the pyramidalization angle at the active site. Our descriptor enables ready identification of the optimal diameter and the best doping type for the CNT surfaces, which is not possible with usual descriptors such as OH species adsorption. As a result, ORR geometric descriptors are very promising since their performance is comparable to that of electronic descriptors. In addition, they are less time-demanding in computation, and they are less sensitive to the accuracy of the calculation method.

Benchmarking Density Functional Theory Based Methods To Model NiOOH Material Properties: Hubbard and van der Waals Corrections vs Hybrid Functionals.

NiOOH has recently been used to catalyze water oxidation by way of electrochemical water splitting. Few experimental data are available to rationalize the successful catalytic capability of NiOOH. Thus, theory has a distinctive role for studying its properties. However, the unique layered structure of NiOOH is associated with the presence of essential dispersion forces within the lattice. Hence, the choice of an appropriate exchange-correlation functional within Density Functional Theory (DFT) is not straightforward. In this work, we will show that standard DFT is sufficient to evaluate the geometry, but DFT+U and hybrid functionals are required to calculate the oxidation states. Notably, the benefit of DFT with van der Waals correction is marginal. Furthermore, only hybrid functionals succeed in opening a bandgap, and such methods are necessary to study NiOOH electronic structure. In this work, we expect to give guidelines to theoreticians dealing with this material and to present a rational approach in the choice of the DFT method of calculation.

Metal-Oxygen Bond Ionicity as an Efficient Descriptor for Doped NiOOH Photocatalytic Activity.

The computational design of solid catalysts has become a very "hot" field during the last decades, especially with the recent increase in computational tool performance. However, theoretical techniques are still very time demanding because they require the consideration of many adsorption configurations of the reaction intermediates on the surface. Herein, we propose to use the metal-oxygen (M-O) bond ionicity as a descriptor for the photocatalytic activity of one of the best catalysts for the oxygen evolution reaction (OER). Ionicity is a bulk property and thus carries the advantage of being easily obtainable from a simple Bader charge analysis by using density functional theory (DFT). We will show that this criterion can be used successfully to design efficient dopants for NiOOH material. This catalyst is known to exhibit interesting photoelectrochemical properties for OER if it is doped with specific transition metals. Finally, we demonstrate that other electronic properties that relate to bulk calculation, such as oxidation states and density of states, are not alone sufficient to explain the photocatalytic activity of the material. Thus, M-O bond ionicity attracts significant interest compared with other bulk observables obtained by using DFT computations.

Role of water in metal catalyst performance for ketone hydrogenation: a joint experimental and theoretical study on levulinic acid conversion into gamma-valerolactone.

While Ru is a poor hydrogenation catalyst compared to Pt or Pd in the gas phase, it is efficient under aqueous phase conditions in the hydrogenation of ketones such as the conversion of levulinic acid into gamma-valerolactone. Combining DFT calculations and experiments, we demonstrate that water is responsible for the enhanced reactivity of Ru under those conditions.