Chitosan -NH2 derived efficient Co3O4 catalyst for styrene catalytic oxidation: Simultaneously regulating particle size and Co valence.

In this study, a Co3O4 catalyst is synthesised using the chitosan-assisted sol-gel method, which simultaneously regulates the grain size, Co valence and surface acidity of the catalyst through a chitosan functional group. The complexation of the free -NH2 complex inhibits particle agglomeration; thus, the average particle size of the catalyst decreases from 82 to 31 nm. Concurrently, Raman spectroscopy, hydrogen temperature-programmed reduction, electron paramagnetic resonance spectroscopy and X-ray photoelectron spectroscopy experiments demonstrate that doping with chitosan N sources effectively modulates Co2+ to promote the formation of oxygen vacancies. In addition, water washing after catalyst preparation can considerably improve the low-temperature (below 250 °C) activity of the catalyst and eliminate the side effects of alkali metal on catalyst activity. Moreover, the presence of Brønsted and Lewis acid sites promotes the adsorption of C8H8. Consequently, CS/Co3O4-W presents the highest catalytic oxidation activity for C8H8 at low temperatures (R250 °C = 8.33 µmol g-1 s-1, WHSV = 120,000 mL hr-1∙g-1). In situ DRIFTS and 18O2 isotope experiments demonstrate that the oxidation of the C8H8 reaction is primarily dominated by the Mars-van Krevelen mechanism. Furthermore, CS/Co3O4-W exhibits superior water resistance (1- and 2- vol% H2O), which has the potential to be implemented in industrial applications.

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.

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.

Controllable P Doping of the LaCoO3 Catalyst for Efficient Propane Oxidation: Optimized Surface Co Distribution and Enhanced Oxygen Vacancies.

The properties of LaCoO3 are modified by a controllable P doping strategy via a simple sol-gel route. It is demonstrated that appropriate P doping is beneficial for forming a relatively pure perovskite phase and hinders the growth of perovskite nanoparticles. The combined results of density functional theory (DFT), extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge structure (XANES), temperature-programmed reduction of hydrogen (H2-TPR), X-ray photoelectron spectroscopy (XPS), and temperature-programmed desorption of ammonia (NH3-TPD) reveal that appropriate P doping gives rise to more oxygen vacancies, optimized distribution of Co ions, and improved surface acidity, which are beneficial for the adsorption of active oxygen species and the activation of propane molecules, resulting in an excellent catalytic oxidation performance. Especially, LaCo0.97P0.03O3 exhibits more surface-active oxygen species, higher bulk Co3+ proportion, increased surface Co2+ species, and increased acidity, resulting in its superior propane oxidation performance, which is dominated by the Langmuir-Hinshelwood mechanism. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) confirms that the presence of P will accelerate oxygen mobility, which in turn promotes the oxidation rate. Moreover, the obtained LaCo0.97P0.03O3 catalyst displays excellent thermal stability during the 60 h durability test at 400 °C and strong resistance against 5 vol % H2O and/or 5 vol % CO2 for prolonged 150 h.