Preparation of cobalt-copper-aluminum spinel mixed oxides from layered double hydroxides for total oxidation of benzene

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.

Catalytic activity and stability of a Cr modified Co–Fe LDO catalyst in the simultaneous catalytic reduction of NOx and oxidation of o-DCB

In this paper, a Co–Fe LDO catalyst was prepared by combining K2Cr2O7 and Cr(NO3)3 to modify the LDH precursor.

Enhanced catalytic performance for VOCs oxidation on the CoAlO oxides by KMnO4 doped on facile synthesis

The MnO_x was immobilized on the CoAl mixed oxides (CoAlO) derived from hydrotalcites with various anions (CO₃^2-, Cl^-, NO₃^- and SO₄^2-) using the hydration and impregnation methods. The CoAlO oxides modified by KMnO₄ were calcined in air at 300 °C to obtain stable oxides, which could be used as catalysts for VOCs (acetone and ethyl acetate) oxidation. CoAlO with CO₃^2- and 30 h of hydration time (CoAlO-C-Mn-30) exhibited a promising catalytic activity (T₉₀ = 173 °C for acetone oxidation; T₉₀ = 175 °C for ethyl acetate), highly superior to CoAlO without KMnO₄ modification. The improvement in acetone and ethyl acetate catalytic oxidation was ascribed to the Co³⁺ and surface adsorbed oxygen species. The increase of Co³⁺ in the CoAlO-C-Mn-30 oxide thanked to the self-decomposition of KMnO₄ and reducibility of Co²⁺ in the CoAlO oxide during the hydration process. This was also confirmed by XRD and XPS characterization, which showed that Mn cations were enriched on the catalyst surface in the valences of +3 and +4. The catalytic activity of the catalyst remained unchanged in four cycles in the presence of 5.5 vol.% water vapor, which indicated a great potential for industrial application.

Oxidation of acetone over Co-based catalysts derived from hierarchical layer hydrotalcite: Influence of Co/Al molar ratios and calcination temperatures

In order to enhance catalytic performance for acetone, Co-based catalysts prepared under different Co/Al molar ratios and calcination temperatures have been studied in this work. The results indicated that the catalytic activities of the catalysts firstly increased and then decreased with the increase of the Co/Al molar ratio and decreased with the increase of the calcination temperature. Based on the catalytic activities, TG/DTA, XRD, TPR and XPS characterization results, it can be found that catalytic activities of the catalysts with various Co/Al molar ratios were effected by the good crystallization structure of catalyst precursor, surface Co³⁺/Co²⁺ molar ratio, low temperature reducibility, and O_ads/O_latt molar ratio of the catalysts. Meanwhile, the catalytic activities of the catalysts with different calcination temperatures depended on the low temperature reducibility, surface Co³⁺/Co²⁺ molar ratio, porous structure and crystallization structure of the catalyst. Among different synthetic composition, 5:1 CoAlO-300 catalyst (T_90% = 225 °C) and 5:1 CoAlO-200 catalyst (T_90% = 222 °C) exhibited the efficient acetone oxidation.