Fabrication of Nanohybrid Spinel@CuO Catalysts for Propane Oxidation: Modified Spinel and Enhanced Activity by Temperature-Dependent Acid Sites
Bin Wang, Guangpeng Yang, Qilei Yang, Bing Li, Dong Wang, Yue Peng, Junhua Li, Chunmei Lu, John C. Crittenden
Abstract
Modulating the catalyst electronic structure is a promising direction to enhance the catalytic oxidation performance. Herein, we report an innovative synthesis of the nanohybrid spinel@CuO catalyst with a broad biphasic interface for propane oxidation. The reaction rate of spinel@CuO catalyst was significantly increased compared to the physically mixed spinel+CuO catalyst. Lattice distortions and severe blurring of lattice fringes adjacent to the interface (between the spinel and CuO) comes with the spinel@CuO system, which enhanced interfacial interaction to form defect structures. The cobalt cations were selectively doped into the spinel lattice and occupied both the A and the B sites, while the CuO was not affected. At lower temperatures (∼200 °C), the enrichment of Brønsted acid sites increased the adsorption energy of propane. At higher temperatures (∼350 °C), the A and B sites cobalt weakened the Cu-O bond to make the oxygen vacancies form more readily, thereby enriching the Lewis acid sites. The substitution doping also resulted in lattice distortion in the spinel species, promoting the formation of a defect structure. The broad interface and temperature-dependent acid sites were conducive to propane oxidation.