Replacing sluggish oxygen evolution reaction (OER) with electrocatalytic oxidation (ECO) of alcohols was a promising hotspot due to its advantages of requiring low potential, inhibiting mixing of gases, and forming value-added products. In the ECO of alcohols process, Fe electron centers of Fe-based layered double hydroxides (LDHs) can regulate the d band of LDHs overlap, optimize the active local structure of LDHs, and then enhance the electrocatalytic oxidation performance. In this work, CoxFey-LDHs nanosheets with different ratios of Co/Fe were prepared for selective ECO of benzyl alcohol (BA) to benzoic acid (BAC). Comprehensive characterizations revealed that the adjustment of bandgap and OH species adsorption of CoxFey-LDHs resulted in the appropriate thermodynamic driving force, which improved the electrical conductivity of CoxFey-LDHs and enhanced their ECO of BA. Especially, the as-prepared Co3Fe1-LDH showed intriguing electrocatalytic activity and only required a potential of 1.51 V (vs. RHE) to achieve a total current density of 50 mA cm−2 in alkaline solution containing 10 mM BA with a conversion (96.79%) of BA and selectivity (94.93%) of BAC, which was 60 mV lower than that of OER. After six cycles, Co3Fe1-LDH still achieved 94.74% conversion of BA and 92.10% selectivity of BAC without significant degradation.
Monthly Archives: September 2023
[ASAP] Functional Alkali Metal-Based Ternary Chalcogenides: Design, Properties, and Opportunities
Chemistry of Materials
DOI: 10.1021/acs.chemmater.3c01652
Toward accurate modeling of structure and energetics of bulk hexagonal boron nitride
This work centers around the evaluation of various computational DFT-based methods in their ability to correctly predict equilibrium lattice constants while at the same time producing reliable interaction energies for h-BN as a prime example of both a covalent as well as weakly bound system. The state-of-the-art fixed-node diffusion quantum Monte Carlo method provided a reference estimate of the bulk h-BN exfoliation energy.
Abstract
Materials that exhibit both strong covalent and weak van der Waals interactions pose a considerable challenge to many computational methods, such as DFT. This makes assessing the accuracy of calculated properties, such as exfoliation energies in layered materials like hexagonal boron nitride (h-BN) problematic, when experimental data are not available. In this paper, we investigate the accuracy of equilibrium lattice constants and exfoliation energy calculation for various DFT-based computational approaches in bulk h-BN. We contrast these results with available experiments and reference fixed-node diffusion quantum Monte Carlo (QMC) results. From our reference QMC calculation, we obtained an exfoliation energy of −33±$$ -33\pm $$2 meV/atom (-0.38±$$ \pm $$0.02 J/m2$$ {}^2 $$).
Probe Beam Dichroism and Birefringence in Stimulated Raman Scattering in Polyatomic Molecules
The contributions of the dichroism and birefringence to the SRS signal depend strongly on the energy level structure of the molecular sample. They can be separated experimentally by using an appropriate probe beam polarization analyzer installed in front of the photodetector (D).
Abstract
Dichroism and birefringence in Stimulated Raman Scattering (SRS) in polyatomic molecules were studied theoretically. General expressions describing the change of the polarization matrix of the probe laser beam transmitted through initially isotropic molecular sample excited by the pump laser beam have been derived. Arbitrary polarization states and propagation directions of the incoming pump and probe beams were considered. The expressions were written in terms of spherical tensor operators that allowed for separation of the field polarization tensor and the molecular part containing three scalar values of nonlinear optical susceptibility with =0,1,2. The geometry of almost collinear propagation of the pump and probe beams through the molecular sample was considered in greater details. It was shown that the dichroism and birefringence refer to the nonlinear optical susceptibility element and that their contributions to the SRS signal can be separated experimentally by using an appropriate probe beam polarization analyzer installed in front of the photodetector. Particular cases of the off-resonant SRS and resonant SRS have been considered. The results obtained were expressed in terms of the Stokes polarization parameters of the pump and probe beams.
Palladium‐Catalyzed Regioselective C‐H Oxidative Arylation of 7‐Azaindazole N‐Oxide at the C6 Position
A new strategy is reported for the C-H/C-H functionalization of 7-azaindazoles at the C6 position via a regioselective oxidative arylation using N-oxide activation. This methodology allowed selective and original access to C6-arylated 7-azaindazoles with different substituted arenes and heteroarenes.
Photolysis of Phosphaketenyltetrylenes with a Carbazolyl Substituent
Carbazolyl-stabilised phosphaketenyltetrylenes were prepared and photolytically decarbonylated. The germylene and stannylene derivatives afforded diphosphene-type dimers, while the plumbylene displayed an unexpected isomerisation reaction and incomplete decarbonylation.
Abstract
Phosphaketenes of divalent group 14 compounds can potentially serve as precursors for the synthesis of heavy multiple-bond systems. We have employed the dtbpCbz substituent (dtbpCbz=1,8-bis(3,5-ditertbutylphenyl)-3,6-ditertbutylcarbazolyl) to prepare such phosphaketenyltetrylenes [(dtbpCbz)EPCO] (E=Ge, Sn, Pb). While the phosphaketenyltetrylenes are stable at ambient conditions, they can be readily decarbonylated photolytically. For the germylene and stannylene derivatives, dimeric diphosphene-type products [(dtbpCbz)EP]2 (E=Ge, Sn) were obtained. In contrast, photolysis of the phosphaketenylplumbylene, via isomerisation of the [(dtbpCbz)PbP] intermediate to [(dtbpCbz)PPb], afforded an unsymmetric and incompletely decarbonylated product [(dtbpCbz)2Pb2P2CO] formally comprising a [(dtbpCbz)PPb] and a [(dtbpCbz)PbPCO] moiety.
Impact of Electrolyte Composition on Bulk Electrolysis of Furfural over Platinum Electrodes
Partial oxidation of furanic biomass derivatives such as furfural is of interest for the sustainable production of chemicals including furoic acid, maleic acid, and 2,5-furandicarboxylic acid (FDCA). The oxidative bulk electrolysis of furfural is here investigated on platinum electrodes in acidic media. The effects of potential, concentration, pH, and supporting anion are studied, and selectivity trends are coupled with attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) to illuminate adsorbate structures that influence the catalysis. Increasing potential is found to shift selectivity from primarily C5 products to C4 products, coincident with oxidation of the Pt surface. Selectivity changes are also observed moving from pH 1 to pH 4, with an increase in C5 products at higher pH. Changing from the weakly adsorbing perchlorate anion to the specifically-adsorbing phosphate anion results in a number of changes that manifest differently depending on potential and pH. Selectivity to furoic acid is found to be highest above the pKa of phosphoric acid due to the strongly adsorbed phosphate ions suppressing flat-lying configurations of furfural that lead to C-C cleavage. These results point toward opportunities to use electrolyte engineering to tune selectivity and optimize surface conditions to disfavor binding of inhibitory products.
Platinum‐DNA Origami Hybrid Structures in Concentrated Hydrogen Peroxide
DNA origami nanostructures are surprisingly stable in up to 5 % hydrogen peroxide over the course of three days and can thus be rendered catalytically active through efficient and reliable coupling to platinum nanoparticles.
Abstract
The DNA origami technique allows fast and large-scale production of DNA nanostructures that stand out with an accurate addressability of their anchor points. This enables the precise organization of guest molecules on the surfaces and results in diverse functionalities. However, the compatibility of DNA origami structures with catalytically active matter, a promising pathway to realize autonomous DNA machines, has so far been tested only in the context of bio-enzymatic activity, but not in chemically harsh reaction conditions. The latter are often required for catalytic processes involving high-energy fuels. Here, we provide proof-of-concept data showing that DNA origami structures are stable in 5 % hydrogen peroxide solutions over the course of at least three days. We report a protocol to couple these to platinum nanoparticles and show catalytic activity of the hybrid structures. We suggest that the presented hybrid structures are suitable to realize catalytic nanomachines combined with precisely engineered DNA nanostructures.
Dynamic Structural Evolution of CeO2 in CuO−CeO2 Catalyst Revealed by In Situ Spectroscopy
The structural evolution of CeO2 in CeO2−CuO catalyst was captured by in situ technique. Under reductive conditions, CeO2 was exposed to the catalyst surface to form an inverse CeOx/Cu interface with a high WGS activity. After the removing of the reductive condition, CeO2 in the catalyst will undergo a surface reconstruction, which is manifested as oxygen migration and oxidation of Cu.
Abstract
The oxides and active metals at the interface synergistically activate reactants and thus promote the reaction, but the interface structure often changes dynamically during the reaction. In the conventional supported catalysts, the metals at the interface have been extensively studied, while the structural evolution of oxides is often overlooked due to the interference of the bulk phase signal. In this work, CeO2−CuO inverse catalysts are designed to reveal the dynamic structure evolution of CeO2 in the CeO2−CuO system during the water gas shift (WGS) reaction by in situ Raman, in situ XRD, quasi in situ XPS, and near ambient pressure XPS (NAP-XPS). CeO2 is partially concealed in the CuO phase in the un-pretreated catalyst and gradually exposed to the surface, forming an inverse CeO x /Cu structure during the reducing process. This structure exhibits a high catalytic activity in the WGS reaction and remains durable under the reductive conditions. When the inverse CeO x /Cu structure is exposed to the non-redox conditions, the reconfiguration of the reduced oxide is observed which is caused by the oxygen migration of CeO2. This work explores the structure evolution of CeO2 in CeO2−CuO inverse catalyst under different conditions by in situ characterization technique and provides a reference for monitoring the dynamic changes of oxide structure.
Preparation and Characterization of Hollow CeO2 Nanoparticles for the Efficient Conversion of CO2 into Dimethyl Carbonate
Hollow CeO2 nanoparticles mesoporous defects were prepared by a solid template method, and showed good catalytic performance for the conversion of CO2 into DMC owing to its abundant mesoporous defects and high oxygen vacancy concentration.
Abstract
The hollow CeO2 (H-CeO2) nanoparticles with mesoporous defects structure were prepared by a solid template method under ambient pressure and applied to catalyze the conversion of CO2 into dimethyl carbonate (DMC). The textural properties of H-CeO2 were investigated by various characterization techniques. The results showed that H-CeO2 have higher surface area, more mesoporous defects and higher surface oxygen vacancies concentration than those of conventional CeO2 with block morphology (C-CeO2). Therefore, H-CeO2 exhibited better catalytic performance for the conversion of CO2 into DMC. Additionally, the Ce(NO3)3 ⋅ 6H2O amount in preparation procedure was important for the formation of hollow structure and mesoporous defects. The DMC yield could reach 4.96 % on H-CeO2-1.2 (Ce(NO3)3 ⋅ 6H2O amount: 1.2 g) catalyst when the reaction was performed at 140 °C and 4.5 MPa for 4 h. This work proposed a facile strategy for designing CeO2 catalysts for the CO2 conversion by creating mesoporous defective structure.