Facile fabrication of Ce-decorated composition-tunable Ce@ZnCo2O4 core-shell microspheres for enhanced catalytic propane combustion

Engineering Oxygen Vacancies of Co-Mn-Ni-Fe-Al High-Entropy Spinel Oxides by Adjusting Co Content for Enhanced Catalytic Combustion of Propane

Transition metal-based oxides with similar oxidation activities for catalytic hydrocarbon combustion have attracted much attention. In this study, a new class of metal high-entropy oxides (CoxMnNiFeAl)3O4 (x = 1, 2, 3, 4, 5) with a porous structure was fabricated through a simple and inexpensive NaCl template-assisted sol-gel approach, which was employed for the catalytic oxidation of propane. The results indicated that the content of cobalt has a great impact on its activity, and the (Co4MnNiFeAl)3O4 catalyst exhibited the best catalytic activity. At the high space velocity of 60 000 mL·g-1·h-1, the optimized one with high-temperature treatment can still achieve 90% propane conversion at 309 °C, which is 68 and 178 °C lower than those of the (CoMnNiFeAl)3O4 catalyst and pure cobalt oxide, respectively. Meanwhile, it has the lowest apparent activation energy (46.6 KJ·mol-1) and the fastest reaction rate (26.976 × 10-6 mol·gcat-1·s-1 at 290 °C). The improved performance of the (Co4MnNiFeAl)3O4 catalyst could be attributed to the enhancement of low-temperature reducibility, the increased number of reactive surface oxygen species, and the cocktail effect of the high-entropy oxides. This work provides new insights into the preparation of efficient light alkane degradation catalysts and a realistic approach for the large-scale application of high-entropy oxides in the field of oxidation catalysts.

Redox-induced controllable engineering of MnO2-MnxCo3-xO4 interface to boost catalytic oxidation of ethane

Multicomponent oxides are intriguing materials in heterogeneous catalysis, and the interface between various components often plays an essential role in oxidations. However, the underlying principles of how the hetero-interface affects the catalytic process remain largely unexplored. Here we report a unique structure design of MnCoOx catalysts by chemical reduction, specifically for ethane oxidation. Part of the Mn ions incorporates with Co oxides to form spinel MnxCo3-xO4, while the rests stay as MnO2 domains to create the MnO2-MnxCo3-xO4 interface. MnCoOx with Mn/Co ratio of 0.5 exhibits an excellent activity and stability up to 1000 h under humid conditions. The synergistic effects between MnO2 and MnxCo3-xO4 are elucidated, in which the C2H6 tends to be adsorbed on the interfacial Co sites and subsequently break the C-H bonds on the reactive lattice O of MnO2 layer. Findings from this study provide valuable insights for the rational design of efficient catalysts for alkane combustion.

Beneficial Synergistic Intermetallic Effect in ZnCo2O4 for Enhancing the Limonene Oxidation Catalysis

Utilization of naturally occurring limonene from renewable biomass as a key starting material for the synthesis of valuable chemicals is a promising avenue to reduce both the dependence on nonrenewable fossil fuels and global CO2 emission. Herein, we report a highly active tremella-like ZnCo2O4 catalyst for the selective oxidation of limonene with molecular oxygen under mild reaction conditions. The developed ZnCo2O4 catalyst exhibits an appealing reaction performance with a limonene conversion of 93.5% (reaction rate of 0.0823 mmol gcat-1 h-1) and selectivity of 75.8% for 1,2-limonene oxide (LO), far outperforming the monometallic oxides of ZnO and Co3O4. Detained experimental characterizations and analyses manifest that the substitution of Zn into the Co3O4 framework can facilitate the formation of more unsaturated coordination sites and oxygen vacancies due to the modified chemical environment of Co atoms, inducing a beneficial synergistic intermetallic effect for the limonene oxidation catalysis.

N-doped CoAl oxides from hydrotalcites with enhanced oxygen vacancies for excellent low-temperature propane oxidation

A series of nitrogen-doped CoAlO (N-CoAlO) were constructed by a hydrothermal route combined with a controllable NH₃ treatment strategy. The effects of NH₃ treatment on the physico-chemical properties and oxidation activities of N-CoAlO catalysts were investigated. In comparison to CoAlO, a smallest content decrease in surface Co³⁺ (serving as active sites) while a largest increased amount of surface Co²⁺ (contributing to oxygen species) are obtained over N-CoAlO/4h among the N-CoAlO catalysts. Meanwhile, a maximum N doping is found over N-CoAlO/4h. As a result, N-CoAlO/4h (under NH₃ treatment at 400°C for 4 hr) with rich oxygen vacancies shows optimal catalytic activity, with a T₉₀ (the temperature required to reach a 90% conversion of propane) at 266°C. The more oxygen vacancies are caused by the co-operative effects of N doping and suitable reduction of Co³⁺ for N-CoAlO/4h, leading to an enhanced oxygen mobility, which in turn promotes C₃H₈ total oxidation activity dominated by Langmuir-Hinshelwood mechanism. Moreover, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs) analysis shows that N doping facilities the decomposition of intermediate species (propylene and formate) into CO₂ over the catalyst surface of N-CoAlO/4h more easily. Our reported design in this work will provide a promising way to develop abundant oxygen vacancies of Co-based catalysts derived from hydrotalcites by a simple NH₃ treatment.

A CeCoOx Core/Nb2 O5 @TiO2 Double-Shell Nanocage Catalyst Demonstrates High Activity and Water Resistance for Catalytic Combustion of o-Dichlorobenzene

A series of catalysts with different core-shell structures has been successfully prepared by a hydrothermal method. They consisted of CeCoO_x @TiO₂ (single shell), CeCoO_x @Nb₂ O₅ (single shell) and CeCoO_x @Nb₂ O₅ @TiO₂ (double shell) core-shell nanocages and CeCoO_x nanocages, in which CeCoO_x was the core and TiO₂ and Nb₂ O₅ were shells. The influence of the core-shell structure on the catalytic performance of o-dichlorobenzene was investigated by activity, water-resistance, and thermal stability tests as well as catalyst characterization. The temperatures corresponding to 90 % conversion of o-dichlorobenzene (T₉₀ ) of CeCoO_x , CeCoO_x @TiO₂ , CeCoO_x @Nb₂ O₅ , and CeCoO_x @Nb₂ O₅ @TiO₂ catalysts were 415, 383, 362 and 367 °C, respectively. CeCoO_x @Nb₂ O₅ exhibited excellent catalytic activity, mainly owing to the special core-shell structure, large specific surface area, abundant activity of Co³⁺ , Ce³⁺ , Nb⁵⁺ , strong reducibility, and more active oxygen vacancies. It can be seen that the Nb₂ O₅ coating can greatly improve the catalytic activity of the catalyst. In addition, due to the protective effect of the TiO₂ shell on CeCoO_x , CeCoO_x @Nb₂ O₅ @TiO₂ catalysts exhibited outstanding thermal and hydrothermal stability for 20 hours. The T₉₀ of CeCoO_x @Nb₂ O₅ @TiO₂ was slightly lower than that of CeCoO_x @Nb₂ O₅ , but it had higher stability and hydrothermal stability. Furthermore, possible reaction pathways involving the Mars-van-Krevelen (MvK) and Langmuir-Hinshelwood (L-H) models were deduced based on studies of the temperature-programmed desorption of O₂ (O₂ -TPD), X-ray photoelectron spectroscopy (XPS), and in situ diffuse reflectance FTIR spectroscopy (DRIFTS) characterization.

Boosting total oxidation of propane over CeO2@Co3O4 nanofiber catalysts prepared by multifluidic coaxial electrospinning with continuous grain boundary and fast lattice oxygen mobility

A one-dimensional (1D) core-shell of Co-Ce oxide has been prepared by multifluidic coaxial electrospinning method and evaluated for the total oxidation of propane (C₃H₈). Activity and morphological characterizations show that the CeO₂@Co₃O₄ nanofiber catalyst, of which the core is CeO₂ and the shell is Co₃O₄, exhibits excellent oxidation activity. The exposed Co₃O₄ grown on the outside of the fibers can rapidly react with C₃H₈ while CeO₂ with high oxygen storage capacity in the inside is conductive to the enhanced oxidation rate. Besides, the continuous grain boundary provides a fast mass transfer channel for lattice oxygen, and rich oxygen vacancies favor the mobility of active oxygen species. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs) confirms that the CeO₂@Co₃O₄ catalyst have a faster rate of C₃H₈ adsorption and better oxidation activity with respect to the counterpart using a single-needle electrospinning method. Moreover, the CeO₂@Co₃O₄ catalyst displays excellent thermal stability, and strong resistance against 5 vol% H₂O and 5 vol% CO₂ at both 300 and 400 °C. Our strategy can give some new insights into morphological engineering to promote active oxygen mobility via the construction of one-dimensional core-shell of metal oxides for catalytic oxidation of VOCs.

A review of confined-structure catalysts in the catalytic oxidation of VOCs: synthesis, characterization, and applications

This picture depicts the process of the catalytic oxidation of VOCs on confined-structure catalysts, which possess excellent activity and can effectively protect the active phase from aggregation and poisoning.

A facile route to prepare mixed transition metal oxide yolk-shell microspheres for enhanced lithium storage

A coordination co-precipitation route followed by a calcination process was developed to prepare mixed transition metal oxide microspheres with a yolk-shell structure. ZnCo2O4, NiCo2O4, MnCo2O4, ZnMn2O4 and CoMn2O4 have been successfully fabricated, which demonstrates the universality of this route. As a promising anode for lithium-ion batteries (LIBs), ZnCo2O4 was investigated as a typical example, which showed a remarkable reversible capacity of 1063 mA h g-1 after 50 cycles at a current density of 200 mA g-1 and a good rate capability of 839 mA h g-1 after 200 cycles at a large current density of 900 mA g-1. This work shows the extensive potential of a general route for the synthesis of yolk-shell microspheres for next-generation energy conversion and storage devices.

Highly improved acetone oxidation activity over mesoporous hollow nanospherical MnxCo3−xO4 solid solutions

Mesoporous hollow nanospherical Mn_xCo_3−xO₄ solid solutions synthesized by a facile solvothermal alcoholysis have been developed to catalyze acetone oxidation for the first time.