Fabrication of Nanohybrid Spinel@CuO Catalysts for Propane Oxidation: Modified Spinel and Enhanced Activity by Temperature-Dependent Acid Sites

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.

Construction of Hollow Cobalt Tetroxide Nanocages through the Metal Salt Bifunctional Etching Strategy for Catalytic Oxidation of Propane at Ultrahigh Space Velocity

“…On the surface of spinel Co 3 O 4 , more Co 2+ was conducive to the generation of more surface oxygen vacancies, which can promote the adsorption of gaseous oxygen, forming more surface-adsorbed oxygen and further improve the catalytic activity. 43,44 The sample Co 3 O 4 −30 exposed more surface Co 2+ and adsorbed oxygen and thus obtained the highest catalytic activity among the samples. Besides, there was a slight increase in the surface hydroxyl groups when the etching concentration reached 20 g/L and above.…”

“…According to the Mars-van Krevelen mechanism, the surface-adsorbed oxygen and the oxygen vacancies are crucial to the activity during the catalytic oxidation of propane. On the surface of spinel Co 3 O 4 , more Co 2+ was conducive to the generation of more surface oxygen vacancies, which can promote the adsorption of gaseous oxygen, forming more surface-adsorbed oxygen and further improve the catalytic activity. , The sample Co 3 O 4 –30 exposed more surface Co 2+ and adsorbed oxygen and thus obtained the highest catalytic activity among the samples.…”

Surface/Lattice Oxygen Synergism of Durable CuO Catalysts for Tandem Dehydrogenation–Oxidation of Glycerol to Carboxylic Acids in Oxygen-Free Medium

“…Different from the previous literature, we did not find it true that for dehydrogenation of GLY in the absence of molecular O 2 , lattice oxygen plays a positive role in formulating key products such as LA and GLYA. It is very interesting to find that the role of surface oxygen has been unclear in most previous reports, as main attention has been paid to understand the activation of Cu–O bond breaking for surface catalytic oxidation chemistry. − In this part, the calcined catalyst samples, despite showing a decreased O a content compared with the as-precipitated samples (Figure ), exhibit high dependency on the amount of O a for both primary and secondary oxidation reactions. This is because before thermal annealing, most surface oxygen species actually exist in water and −OH (hydroxide) forms, which restrain surface coordination with C–H and O–H bonds in GLY and intermediate molecules.…”

Probing the Actual Role and Activity of Oxygen Vacancies in Toluene Catalytic Oxidation: Evidence from In Situ XPS/NEXAFS and DFT +UCalculation

“…Because we need to consider the apparent reaction rate under the conditions of high conversion, the instant reaction rate (r = −dc/dt) cannot be approximated as the average reaction rate (r = −Δc/t); the definite integral form of the rate equation was applied to this pseudo-first-order reaction. 30,31 Toluene catalytic oxidation performance was also tested under near-ambient pressure conditions. The details are summarized in the Supporting Information.…”