Ce1−xCrxO2−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 Ce 1− x Cr x O 2− 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 H 2 O 2 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, N 2 adsorption, transmission electron microscopy, X‐ray photoelectron spectroscopy, and UV/Vis spectroscopy. It was found that these Ce 0.7 Cr 0.3 O 2− δ nanocrystals are highly active for the selective oxidation of cyclohexane to cyclohexanone/cyclohexanol using H 2 O 2 as an oxidant at low temperature. In the presence of H 2 O 2 at 45 °C for 5 h using Ce 0.7 Cr 0.3 O 2− 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 Cr 6+ content in the Ce 1− x Cr x O 2− δ solid solutions and the formation of highly oxidative intermediates with H 2 O 2 .