Promotional effect of Mn-doping on the catalytic performance of NiO sheets for the selective oxidation of styrene

Experimental and Theoretical Investigation of Interfacial Engineering in Fe2O3/NiFe2O4 Heterostructures toward the Cycloaddition of CO2 with Styrene Oxide

The chemical fixation of CO2 into epoxides for the synthesis of cyclic carbonates is an appealing solution to both reduce global CO2 emission and produce fine chemicals, but it is still a prime challenge to develop a low-cost, earth-abundant, yet efficient solid catalyst. Herein, Fe2O3/NiFe2O4 heterostructures are facilely constructed for the highly efficient cycloaddition of CO2 with styrene oxide (SO) to produce styrene carbonate (SC). Both experimental findings and density functional theory (DFT) calculations substantiate the prominent electron transfer and charge redistribution within the heterointerfaces between the biphasic components, which induce a unique interfacial microenvironment that can facilitate the adsorption and activation of SO. This endows the biphasic catalyst with a substantially higher reactivity than the individual components. This study sheds new insights into the establishment of heterostructured catalysts consisting of transitional metal oxides for the high-efficiency production of SC from the cycloaddition of CO2 with SO.

Tuning the interface of MIMII(OH)F@MIMII1-xS (MⅠ: Ni, Co; MⅡ: Co, Fe) by atomic replacement strategy toward high performance overall water splitting

Constructing heterostructure is considered as one of the most promising strategies to reveal high efficiency hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance. Nevertheless, it is highly challenging to obtain stable interfaces and sufficient active sites via conventional method. In addition, Ni, Co and Fe elements share the valence electron structures of 3d6-84s2, the appropriate integration of these metals to induce synergistic effect in multicomponent electrocatalysts can enhance electrochemical activity. Herein, in this work, the MIMII(OH)F@MIMII1-xS (NiFe(OH)F@NiFe1-xS, NiCo(OH)F@NiCo1-xS, CoFe(OH)F@CoFe1-xS) autogenous heterostructure on nickel foam are constructed. As a result, NiFe(OH)F@NiFe1-xS-0.05, NiCo(OH)F@NiCo1-xS-0.05, and CoFe(OH)F@CoFe1-xS-0.05 demonstrate outstanding overpotential for HER (70 mV, 90 mV, 81 mV at -10 mA cm-2) and OER (370 mV, 470 mV, 370 mV at 10 mA cm-2) in alkaline electrolyte, while the overpotential for HER is 176 mV, 189 mV, 167 mV at -10 mA cm-2 and corresponding OER is 290 mV, 390 mV, 300 mV at 10 mA cm-2 in simulated seawater, respectively. In addition, the NiFe, NiCo, CoFe-based electrolyzer acquire favorable overall water splitting activity in alkaline (1.72 V, 1.87 V, 1.66 V) and simulated seawater (1.73 V, 1.75 V, 1.69 V) at 10 mA cm-2. Overall, the above results authenticate the feasibility of developing autogenous heterostructure electrocatalysts for providing hydrogen and oxygen in alkaline and simulated seawater.

Nickel Hydroxide Nanosheets Prepared by a Direct Manual Grinding Strategy for High-Efficiency Catalytic Combustion of Methane

Nickel hydroxide nanosheets were prepared by a very simple direct manual grinding strategy and then calcined at 200, 300, 400, and 500°. The synthesized samples were tested in lean methane (1.0% CH₄, air balanced) catalytic combustion and subjected to a series of physical and chemical characterizations. The sample calcined at 200 °C (Ni(OH)₂-200) presented a typical nanosheet structure and the best methane catalytic activity in all the samples, which can completely catalyze methane at 400 °C. The crystal structure changed from β-Ni(OH)₂ to NiO at a calcination temperature of 300 °C. The β-Ni(OH)₂ nanosheets began to partially agglomerate into nanoparticles at 400 °C and almost transformed into nanoparticles at 500 °C. Interestingly, the original nanosheet samples Ni(OH)₂-200 and NiO-300 still maintained their morphology and structure although they all went through an activity test at 500 °C in a 1.0% CH₄ atmosphere, which proves that the calcination of nanosheets in a CH₄ atmosphere tended to maintain their nanosheet morphology compared with calcination in the air. Furthermore, through the activity test, X-ray photoelectron spectroscopy results, TPx, and in situ DRIFTS characterization, it was proved that the hydroxyl groups on the Ni(OH)₂-200 and NiO nanosheets were beneficial to the dissociation of methane on the catalyst surface, and the nanosheet structure was also prone to generating more active adsorbed oxygen, so the activation energy of methane was lowered. A methane catalytic mechanism on the Ni(OH)₂ nanosheets and NiO nanoparticles was proposed, which further proved the key role of hydroxyl groups in methane combustion.

High-Performance Styrene Epoxidation with Vacancy-Defect Cobalt Single-Atom Catalysts

Exploring highly active and cost-effective catalysts for styrene epoxidation is of great significance, but it remains challenging to simultaneously achieve excellent conversion and selectivity toward styrene oxide. In this work, the structures and performance of Co, Fe, and Cu single-atom catalysts (SACs) in styrene epoxidation with tert-butyl hydroperoxide (TBHP) are predicted using density functional theory (DFT) calculations. The results reveal that the Co-N structure prefers that of styrene oxide over Fe-N and Cu-N structures. This predicted result is verified via catalytic evaluations, where the Co SACs displayed significantly higher styrene oxide selectivity than Fe and Cu SACs. Moreover, the activity of Co SAC can be further improved by the construction of unsaturated vacancy-defect cobalt single sites. As a result, excellent performance with styrene conversion of 99.9% and styrene oxide selectivity of 71% is achieved after a reaction time of 8 h on the optimal Co SAC.

Pumpkin-derived N-doped porous carbon for enhanced liquid-phase reduction of 2-methyl-4-nitrophenol

Metal-free catalysts with environmental friendless, cost-competitiveness and less susceptibility to leaching and poisoning over metal-based catalysts, have revolutionized in the catalysis domain. In this respect, we herein report the first application of cheap and abundant pumpkin-derived N-doped porous carbon for the reduction of 2-methyl-4-nitrophenol assisted by NaBH₄. The obtained catalyst is cost-competitive, efficient and robust, with an attractive mass-normalized rate constant of 4.73 s^-1 g^-1 and good recycling performance. Systematical analyses demonstrate that the 2-methyl-4-nitrophenol reduction reaction catalyzed by the N-doped carbon proceeds through the Langmuir-Hinshelwood kinetics and the performance enhancement benefits from the strong adsorption and activation of the substrates induced by the electronic modulation in the carbon framework via N-doping. This study opens up new avenues for the high-value use of pumpkin as well as the development of metal-free strategy in more catalytic applications.

Experimental and theoretical investigation of the tuning of electronic structure in SnO2via Co doping for enhanced styrene epoxidation catalysis

Co doping is an effective strategy for the tuning of electronic structure in SnO2, which leads to a huge boost in the styrene epoxidation reaction performance.

Hydroxyl-terminated carbon dots for efficient conversion of cyclohexane to adipic acid

Adipic acid (HOOC(CH₂)₄COOH, AA) is a crucial chemical in industrial manufactures and mainly produced by the oxidation of cyclohexane with air and nitric acid via a homogeneous two step path in industry. However, the conventional industrial method inevitably results in the generation of nitrous oxide (N₂O, etc.), which is the main cause of the greenhouse effect and ozone depletion. Herein, we engineered five kinds of carbon dots (CDs) with different oxygen-containing functional groups on their surfaces, which were directly used as catalysts over the selective catalytic oxidation of cyclohexane. Among the five CDs, the hydroxyl-terminated CDs show the best catalytic activity with the conversion of cyclohexane ~ 29.43% and selectivity to AA ~ 95.89% under 130 °C, 20 atm with oxygen as oxidant. With the CDs directly as catalyst, the one-step efficient catalytic oxidation reaction for cyclohexane to AA was realized to replace the two-step routes. In addition, the density functional theory (DFT) computational results were performed to further prove that the more quantity of hydroxyl on CDs and the higher O₂ pressure can boost the higher catalytic activity of CDs over oxidation of cyclohexane.