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The rational modulation of metal catalysts with tailorable valence and redox properties is a promising strategy for further improving their catalytic performance. Herein, an environment-friendly grafting and thermal strategy was adopted to immobilize copper oxides nanoparticles on carbon nanofiber (CuO x /CF). Benefiting from the defect-rich surface and valence-mixed composition of the CuO x species, the optimized sample CuO x /CF-3 exhibits superb activity for the catalytic reduction of toxic nitrophenols. The complete conversion took only 1 min and an outstanding rate constant (k) of 112.7 × 10˗3 s˗1 was achieved under mild conditions (25 °C and 1 atm). Kinetic and recycle experiments demonstrated that the whole catalytic process obeys a pseudo-order kinetic, and the catalyst could maintain high conversion even after 13 successive recycles. These results demonstrate that CuO x /CF-3 is an alternative catalyst to noble metals, providing superb catalytic efficiency and stability in the reduction of toxic nitrophenols, and it can be expanded to develop other noble-metal-free catalysts for various applications. [Display omitted] • CuO x /CF-3 nanocatalyst was fabricated via a facile two-step strategy. • The uniform dispersion state and defect-rich surface endow the catalyst with unique redox properties. • DFT calculation indicates Cu(I) site is negatively charged by gaining electrons form surrounding O atoms. • Enhanced hydrogenation activity and reusability was achieved over CuO x /CF-3. [ABSTRACT FROM AUTHOR]

The temperature-controlled pyrolysis of inert Co-MOF at 400 °C resulted in the derived CoO x /CN-400 catalyst with inter-connected pore structure and co-dopant of Co 3 O 4 clusters and N-atoms, which greatly improved the redox property of the catalyst, thus achieving improved activity and kinetics and outstanding recyclability in the hydrogenation of nitroarenes under ambient conditions. [Display omitted] • CoO x /CN-400 with hierarchical structure was fabricated via a temperature-controlled pyrolysis strategy. • The co-dopant of CoO x nanoparticles and N-atoms was realized in CoO x /CN-400. • CoO x /CN-400 showed excellent activity and kinetics in the hydrogenation of nitrophenols. • The embedded CoO x nanoparticles endow CoO x /CN-400 with high efficiency for six successful reuses. Developing metal oxide catalysts with comparable activity to precious metals has become a hot but challenging area of research for wastewater purification. Herein, CoO x particles and nitrogen co-doped carbon with a hierarchical structure were designed and synthesized via a temperature-controlled pyrolysis strategy using inert Co-based metal–organic frameworks (Co-MOFs) as precursors. Unlike traditional methods, the exquisite pyrolysis of the Co-MOF at 400 °C enabling the CoO x particles with an average diameter of 6.8 nm to uniformly disperse, thus facilitating the formation of the optimized CoO x /CN-400 composite. Benefiting from the unique morphology and composition, CoO x /CN-400 exhibited improved redox property and exceptional activity for the reduction of nitrophenol to form the corresponding aminophenol compounds. The complete conversion of 4-nitrophenol over CoO x /CN-400 requires only 35 min with a rate constant of 0.12 min−1, which is significantly higher than that of most non-noble metal catalysts and approaching some of the noble metal-based catalysts. Furthermore, leveraging the embedded CoO x particles, CoO x /CN-400 maintains its high catalytic efficiency even after six successive cycles, demonstrates an outstanding long-term catalytic capability and reusability. Finally, the mechanisms of 4-NP reduction have been hypothesized based on the combination of characterization and DTF calculations. [ABSTRACT FROM AUTHOR]

A combined experimental and theoretical study shows that Cu 2 O microspheres with an anti-fluorite crystal phase possess unique capacity of hydrogen activation, therefore exhibited excellent catalytic activity, reaction kinetics and recyclability in a series of nitroarenes hydrogenation reaction under mild conditions. [Display omitted] • Microspheres of Cu, Cu 2 O and CuO were synthesized and structurally characterized. • Cu 2 O exhibited outstanding catalytic capability in nitroarenes reduction under ambient conditions. • Cu 2 O could be reused at least 25 times without significant loss of activity. • Theoretical study confirmed the key role of unique Cu+ sites in Cu 2 O during the reaction. Copper is a crucial element in the field of catalysis. However, Cu-based catalysts exhibit lower redox properties and surface energy under mild conditions, which limit their electron transfer capacities and catalytic performance. In this study, the relationship investigation between the hydrogenation behavior of Cu-based catalysts and crystal phases showed that spherical Cu 2 O exhibited enhanced capacity for hydrogen activation, excellent catalytic activity and outstanding reusability in the selective reduction of various nitroarenes. At even 25 °C and 1 atm, the complete reduction of 4-nitrophenol by NaBH 4 was achieved in 2.5 min over Cu 2 O, achieving a reaction rate constant (k) of 20.15 × 10−3 s−1, which was 4.8 and 15.2 times that of CuO and Cu catalysts. Detailed experimental and theoretical calculations revealed that the Cu+ sites in the antifluorite crystal phase of Cu 2 O are conducive to the adsorption of active H species, while the unique d–s orbital recombination provides more electrons to improve its hydrogenation performance. The results of this study can aid in the development of copper-based materials as advanced catalysts, thereby improving fine chemical production and pollution treatment processes. [ABSTRACT FROM AUTHOR]

The development of advanced catalysts is of vital importance for chemical production, and vacancy engineering represents an effective approach to improve the overall catalytical activities by modulating their structural characters. Herein, a series of oxygen-vacancy-functionalized copper oxides were effectively prepared through a hydrothermal-oxidative tandem process. The optimized CuO-S30 catalyst shows an exceptionally-improved catalytical performance for the selective hydrogenation of 4-nitrophenol (4-NP) with good reusability. With the assistance of theoretical simulation, the exceptional activity can be attributed to the electronic modulation induced by oxygen vacancies in CuO-S30, which could not only facilitate the trapping of the reactants on the positively charged Cu sites, but also promote the electron transfer during the hydrogenation process. This study offers a facile and environmentally friendly strategy for electronic property modulation in metal oxides by oxygen vacancies construction, which can be further extended to other advanced catalysts with outstanding catalytic properties. [Display omitted] • Copper oxides with oxygen vacancy are fabricated via an oxidative etching strategy. • The optimized CuO-S30 exhibited exceptional performance for 4-NP reduction. • Key role of O v towards hydrogen activation by contributing Cuδ+ sites. • Outstanding reusability and low activation energy was achieved over CuO-S30. [ABSTRACT FROM AUTHOR]

• MOF-120 catalyst featuring open metal sites is obtained under mild conditions. • Coordination environments determine geometric and electronic characteristics of MOFs. • Theoretical study reveals that Cu atom at open metal sites exhibits a special charge state. • Enhanced hydrogenation activity and reusability was achieved over MOF-120. Both experimental and theoretical studies demonstrate that metal-organic frameworks functioned with open metal sites boost the adsorption and electron transport from the donors to acceptors, exhibiting excellent catalytic activity and reusability during hydrogenation process. [Display omitted] In this study, a decompression-thermalization strategy was utilized for a Cu-containing metal-organic framework (MOF) to tune its redox and catalytic hydrogenation properties. Remarkably, at just 120 °C, open metal sites (OMSs) were successfully constructed by removing coordinated solvent molecules to generate the daughter MOF-120. The tailored redox property of MOF-120 is correlated with the presence of OMSs. Compared with the pristine MOF where copper cations were capped by DMF, MOF-120 exhibited improved kinetics, showed a reduction of activation energy and outstanding recyclability in the hydrogenation of 4-nitrophenol under mild conditions (25 °C, 1 atm). Both experimental studies and theoretical calculation results reveal that the generation of OMSs endows the Cu species with unique electronic properties, which assist the adsorption and electron transfer between substrate molecules and is responsible for the enhanced performance in the hydrogenation process. [ABSTRACT FROM AUTHOR]