Ce_1−xCr_xO_2−δ Nanocrystals as Efficient Catalysts for the Selective Oxidation of Cyclohexane to KA Oil at Low Temperature under Ambient Pressure

Abstract

The selective oxidation of C−H bonds in saturated hydrocarbons at low temperature with noble‐metal‐free heterogeneous catalysts is a profound challenge for the catalysis community. Here we report the facile synthesis of Ce1−xCrxO2−δ (x=0, 0.1, 0.2, 0.3, and 0.4) nanocrystals through a low‐temperature hydrothermal method. The catalytic activity of the as‐prepared catalysts was evaluated in the selective oxidation of cyclohexane to cyclohexanone/cyclohexanol using H2O2 as an oxidant at room temperature and 45 °C. The activity results were correlated with their phase structure, composition, surface areas, and surface element states with the help of X‐ray diffraction, N2 adsorption, transmission electron microscopy, X‐ray photoelectron spectroscopy, and UV/Vis spectroscopy. It was found that these Ce0.7Cr0.3O2−δ nanocrystals are highly active for the selective oxidation of cyclohexane to cyclohexanone/cyclohexanol using H2O2 as an oxidant at low temperature. In the presence of H2O2 at 45 °C for 5 h using Ce0.7Cr0.3O2−δ as a catalyst, the conversion of cyclohexane reaches 50.3 % and the total selectivity of cyclohexanol/cyclohexanone is 94.4 % with relative good reversibility for at least four cycles. Mechanistic investigation results show that the high activity can be attributed to the high Cr6+ content in the Ce1−xCrxO2−δ solid solutions and the formation of highly oxidative intermediates with H2O2.

Rationally Designed CeO2 Nanosheets over Co9S8 Nanoparticles form S‐Scheme Heterojunction for Efficient Hydrogen Production

“…The characteristic peaks appearing at binding energies of 917.02, 907.69, 903.38, and 901.14 eV could be attributed to the Ce 3+ unit in Ce 3d 3/2 . [ 35,36 ] Peaks corresponding to Ce 3d 9 4f 0 L n , 3d 9 4f 1 L n‐1 , Ce 3d 9 4f 1 L n , and Ce 3d 9 4f 2 L n‐1 appear at binding energies of 898.49, 889.05, 884.64, and 882.50 eV, respectively. [ 37,38 ] The binding energy value of the peak corresponding to Ce 3d in CCS‐3 was not the same as the binding energy value of the peak of the same unit in CeO 2 , indicating that there exists a coupling effect between CeO 2 and Co 9 S 8 .…”

Eutectoid decompositions in Ce‐containing ABO3 perovskites: Part II, the case of divorced growth in CeCrO3

“…Smaller size species, like Nb in CeO 2 , provide a reference and have reported bulk solubility limits of 0.6 mol%. 21 Therefore, Cr enrichment of near-surface regions observed in the STEM-EELS measurements may be driven by strain energy minimization, where the free surface can better accommodate the size mismatch than the bulk region (CeO 2 nanomaterials have been reportedly doped with Cr at concentrations of a few mole percent to values greater than 10 mol% [22][23][24][25][26][27][28] ). With increased annealing times or temperatures there would be a reduction in CeO 2 surface area driven by coarsening of CeO 2 grains, as well as the redistribution of any kinetically trapped Cr solute in the CeO 2 .…”

A one-step method for preparing Cr-doped SiO2: An efficient catalyst for the direct oxidation of cyclohexane to ketone-alcohol oil

“…However, the oxidation process often requires a high temperature and raised air/O 2 pressure. 6,7 Moreover, although porphyrin and other metallic complexes can be used for the selective oxidation of cyclohexane at moderate temperatures and pressures, they require complicated preparation procedures and are difficult to be industrialized. 8–10 Besides, these homogeneous catalyst systems inevitably encounter the problems of catalyst recovery and product separation.…”