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Layered AᴵᴵᴵBᵛᴵ chalcogenides represent an interesting class semiconductors, where most of adopting 2D structures. Unlike the typical sandwiched structure of transition metal dichalcogenides (TMDs), layered AᴵᴵᴵBᵛᴵ chalcogenides like InSe and GaSe are composed of X−M−M−X motif where M is gallium/indium and X is sulfur/selenium/tellurium. The exception is InS, which adopt an orthorhombic 3D structure. Herein, we studied and compared the inherent electrochemical properties as well as the electrocatalytic performances towards hydrogen evolution (HER), oxygen evolution (OER) and oxygen reduction reaction (ORR) of indium monochalcogenides (InS, InSe and InTe). Inherent electrochemistry studies in phosphate buffered saline electrolyte showed that InS did not exhibit any inherent electrochemical signals when compared to bare glassy carbon electrode. However, InSe showed a reduction peak at −1.6 V while InTe had an oxidation peak at 0.2 V. The heterogeneous electron transfer (HET) rates of indium monochalcogenides were measured with [Fe(CN)₆]³⁻⁄ ⁴⁻ redox probe using cyclic voltammetry (vs. Ag/AgCl) at the scan rate of 100 mV s⁻¹. It was found that InTe exhibited the best electrochemical performance with the fastest HET rate with highest k 0 obs obtained (3.7×10⁻³cm s⁻¹). InS showed the best electrocatalytic performance for HER with the lowest overpotential value of 0.92 V at current density of −10 mA cm⁻². However, the performances of indium monochalcogenides were almost comparable to that of bare glassy carbon electrode and do not exhibit any improvements in electrocatalytic capabilities. This study provides insights into the electrochemical properties and electrocatalytic performances of layered AᴵᴵᴵBᵛᴵ indium monochalcogenides which would influence potential applications. M.P. acknowledges the financial support of Grant Agency of the Czech Republic (EXPRO: 19-26896X). K.S. was supported by Specific University Research (MSMT No. 20-SVV/2019). Z.S. was supported by Neuron Foundation for scientific support.

Homogeneous catalytic oxidations of cyclohexene by transition metal substituted phosphotungstates [PW₁₁M(L)O₃₉]m- (PW₁₁M, M = Co(II), Cu(II), Fe(III), Ni(II), Mn(II), L = H₂O or absence) with hydrogen peroxide in acetonitrile were experimentally studied. The catalytic activities of allylic oxidation were found to strongly depend on the transition metals, and PW₁₁Co showed the highest activity. The product distribution and the catalyst stability were dominated by mole ratio of hydrogen peroxide to PW₁₁M, whose low or high led to stable structure of PW₁₁M and predominant formation of allylic oxidation products or decomposition of PW₁₁M. Different from the activation of allylic C-H bond by radicals, the oxidation of C=C double bond was based on tungsten-peroxo species. A reaction mechanism composed of radical and non-radical processes was proposed from nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR) and kinetic data, to describe the reaction pathways of cyclohexene oxidation.

Two kinds of typical mineral-derived Cu/ZnO catalysts consisting of aurichalcite and zincian malachite were introduced for furfural hydrogenation to furfuryl alcohol (FOL) and 2-methylfuran (2-MF) in a fixed-bed reactor. Under proper reaction conditions, high yields of FOL (above 99 %) and 2-MF (94.5 %) could be obtained over the aurichalcite Cu/ZnO catalyst (AC-CZ), whereas the best yield of 2-MF was only 76.9 % (0.5 h−1) over the zincian malachite Cu/ZnO catalyst (ZM-CZ). The normalized productivity of 2-MF was 43.5 mol kgCu−1 h−1 and 17.4 mol kgCu−1 h−1 for AC-CZ and ZM-CZ, respectively (LHSV=1.5 h−1). The catalysts were characterized by XRD analysis, Raman spectra, CO IR spectroscopy, H2 temperature-programmed reduction, N2O titration, NH3 temperature-programmed desorption, and X-ray photoelectron spectroscopy. The far better performance of AC-CZ in furfural hydrogenation was ascribed to its higher dispersion of copper species, superior copper surface area, better surface acidity distribution, and stronger Cu0–ZnO synergy. In addition, the surface acidity of the catalysts seemed to have a higher influence on 2-MF production than the Cu surface area, but the optimal balance of both factors still needs to be investigated systematically.

A study of the promotional effect of potassium on the carburization behavior of a series of spray-dried precipitated Fe2O3 catalysts (100 Fe, 100 Fe/0.52 K, 100 Fe/1.54 K, and 100 Fe/2.4 K) has been performed by using in situ XRD. The average crystallite size evolution for species such as α-Fe2O3, Fe3O4, χ-Fe5C2, and θ-Fe3C were followed. The potassium promoter clearly inhibits the reduction of α-Fe2O3 to Fe3O4, where the decreasing binding energy in the Fe 2p3/2, O 1s and K 2p3/2 spectra from X-ray photoelectron spectroscopy (XPS) suggests an electron density increase in Fe and O upon potassium promotion, leading to the enhanced covalency in the Fe−O bond. In terms of crystallite size during carburization, an optimum potassium loading exists in catalyst 100 Fe/0.52 K, which shows the fastest reduction to Fe3O4 with minimum crystallite sizes of around 7 to 15 nm. Potassium has no clear effect in determining the final crystallite size of χ-Fe5C2. An arch-shaped curve in the evolution of crystallite size of the Fe3O4 intermediate was observed, which can be explained by the activation energy difference between the bidirectional steps of the outward oxygen diffusion and the inward carbon diffusion.

One peculiar type of aza-hetero-imidazolidinyl spirooxindole derivatives was efficiently constructed by the three-component [2+2+1] cascade reaction of 1,4-oxazepines with diazo-oxindoles. Iron(II) trifluoromethanesulfonate [Fe(OTf)2] or p-toluenesulfonic acid monohydrate (p-TsOH⋅H2O) proved to be optimal catalysts for this transformation, providing the desired products in high yields (up to 94 %) with excellent diastereoselectivity (up to 99:1 dr). Experimental studies showed that the reaction rate of Bronsted acid catalysis was faster than that of Lewis acids. Furthermore, the mechanism was theoretically investigated for Bronsted acid as the catalyst and a reaction pathway was proposed. DFT calculations suggested that the diazo-oxindole can act as a 1,3-dipole to add to a C=N double bond of 1,4-oxazepine, which forms a 4,5-dihydro-1H-1,2,3-triazole intermediate. Subsequently, the releasing of N2 is the rate-limiting step of the whole catalytic cycle.

The involvement of oxygen vacancies in the electronic and structural properties and photocatalytic activity of hydrogenated TiO2 (H-TiO2) for water splitting are currently under debate. Herein, the process for the formation of oxygen vacancies in H-TiO2 is illustrated for the first time to verify the role of these vacancies on the surface and in the bulk of H-TiO2 by using surface-sensitive soft X-ray techniques and bulk-information-included hard X-ray techniques for the O K-edges and Ti K-edges, respectively. We find that oxygen vacancies on the surface and in the bulk contribute differently to tailing of the conduction band of H-TiO2. By controlling the degree of hydrogenation to restrict tailing of the conduction band to just above the H+/H2 redox potential, the most favorable disordered structure for photocatalytic H2 evolution is developed. This work promotes a better understanding of the possible negative consequence of hydrogenated semiconductors in H2 evolution apart from the positive effect on visible-light response.

The structural diversity of ionic liquids can control the properties and structures of carbon materials at the molecular level. A nitrogen and boron codoped and highly crystalline metal porous carbon material was synthesized through cothermal condensation of the [Bmim][BF4] (Bmim=1-butyl-3-methylimidazolium) ionic liquid and cobalt(II) 5,10,15,20-tetraphenylporphyrin. In this approach, the ionic liquid acted as both a soft template and a heteroatom precursor. The resulting B-doped Co-N-C nanomaterial showed significantly enhanced catalytic performance toward the selective oxidation of ethylbenzene, in that the conversion of ethylbenzene was approximately four times higher than that of the catalyst without the introduced B atoms. Moreover, the CoNCB-2 catalyst was successfully recycled several times without any significant loss in activity. Such a boron, nitrogen, and metal ternary codoped porous carbon shows promise as a catalyst for chemocatalysis.

The tedious and costly route of the general nanocasting method hinders the commercial application of mesoporous non-precious metal catalysts based on transition metal-coordinating nitrogen-doped carbons (MN/C). Here, a simple, economic and sustainable hydrothermal carbonization (HTC)/soft templating method is demonstrated for the direct preparation of mesoporous FeN/C materials (FeN/MC). By this method, FeN/MC materials with high specific surface area, hierarchically mesoporous structure, and appropriate iron and nitrogen contents are prepared. The optimized FeN/MC materials exhibit superior catalytic performance in the oxygen reduction reaction (ORR) to commercial Pt/C in 0.1 M KOH. This confirms that the materials are one of the most efficient non-precious metal catalysts for the ORR in alkaline electrolyte. In addition, considerable durability and ORR activity are demonstrated by the FeN/MC materials in 0.1 M HClO4. Thus, this HTC/soft templating method has great promise for the practical application of this kind of non-precious metal catalysts in the ORR.

Carbon-supported cobalt nanoparticles with different particle sizes were synthesized and characterized by complementary characterization techniques such as X-ray diffraction, N-2 sorption, acetone temperature-programmed desorption, transmission electron microscopy, and CO chemisorption. Using acetone steam reforming reaction as a probe reaction, we revealed a volcano-shape curve of the intrinsic activity (turnover frequency of acetone) and the CO2 selectivity as a function of the cobalt particle size with the highest activity and selectivity observed at a particle size of approximately 12.8nm. Our results indicate that the overall performance of acetone steam reforming is related to a combination of particle-size-dependent acetone decomposition, water dissociation, and the oxidation state of the cobalt nanoparticles.

Fundamental understanding and control of chemical transformations are essential to the development of technically feasible and economically viable catalytic processes for efficient conversion of biomass to fuels and chemicals. Using an integrated experimental and theoretical approach, we report high hydrogen selectivity and catalyst durability of acetone steam reforming (ASR) on inert carbon supported Co nanoparticles. The observed catalytic performance is further elucidated on the basis of comprehensive first-principles calculations. Instead of being considered as an undesired intermediate prone for catalyst deactivation during bioethanol steam reforming (ESR), acetone is suggested as a key and desired intermediate in proposed two-stage ESR process that leads to high hydrogen selectivity and low methane formation on Co-based catalysts. The significance of the present work also sheds a light on controlling the chemical transformations of key intermediates in biomass conversion such as ketones. We gratefully acknowledge the financial support from U. S. Department of Energy (DOE), Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences, and the Laboratory directed research and development (LDRD) project of Pacific Northwest National Laboratory (PNNL). Computing time was granted by the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL). The EMSL is a U.S. DOE national scientific usermore » facility located at PNNL, and sponsored by the U.S. DOE’s Office of Biological and Environmental Research.« less

Oxidized sulfur and nitrogen co-doped graphitic carbon (SN-G) was one-step synthesized simply by annealing a solid mixture of D-glucosamine hydrochloride, melamine, and trithiocyanuric acid. By tailoring the additive dosage and the pyrolysis temperature, correlations between the structure, composition, and electrochemical performance of SN-G were systematically elucidated. To our excitement, the SN3-G sample pyrolyzed at 900 °C with a dominant oxidized sulfur content exhibited striking electrocatalytic activity in alkaline medium, which was free from the crossover effect, and its long-term durability was superior to that of commercial Pt/C (20 wt %). Furthermore, oxidized sulfur that was reported to be chemically inactive for the ORR was proven to be active, which was supported by both experimental results and density functional theory calculations.