Crystalline Co 3 O 4 nanoparticles with a uniform size of 9 nm as shown by Xray diffraction (XRD) and transmission electron microscopy (TEM) were synthesized by thermal decomposition of cobalt acetylacetonate in oleyl amine and applied in the oxidation of 2-propanol after calcination. The catalytic properties were derived under continuous flow conditions as function of temperature up to 573 K in a fixed-bed reactor at atmospheric pressure. Temperature-programmed oxidation, desorption (TPD), surface reaction (TPSR) and 2-propanol decomposition experiments were performed to study the interaction of 2-propanol and O 2 with the exposed spinel surfaces. Co 3 O 4 selectively catalyzes the oxidative dehydrogenation of 2-propanol yielding acetone and H 2 O and only to a minor extent the total oxidation to CO 2 and H 2 O at higher temperatures. The high catalytic activity of Co 3 O 4 reaching nearly full conversion with 100% selectivity to acetone at 440 K is attributed to the high amount of active Co 3+ species at the catalyst surface as well as surface-bound reactive oxygen species observed in the O 2 TPD, 2-propanol TPD, TPSR, and 2-propanol decomposition experiments. Density functional theory calculations with a Hubbard U term support the identification of fivefold coordinated octahedral surface as the active site, Co 3 + 5c and oxidative dehydrogenation involving adsorbed atomic oxygen was found to be the energetically most favored pathway. The consumption of surface oxygen and reduction of

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Monocrystalline, yet porous mosaic platelets of cobalt ferrite, CoFe O , can be synthesized from a layered double hydroxide (LDH) precursor by thermal decomposition. Using an equimolar mixture of Fe , Co , and Fe during co-precipitation, a mixture of LDH, (Fe Co ) Fe (OH) (CO ) ⋅m H O, and the target spinel CoFe O can be obtained in the precursor. During calcination, the remaining Fe fraction of the LDH is oxidized to Fe leading to an overall Co :Fe ratio of 1:2 as required for spinel crystallization. This pre-adjustment of the spinel composition in the LDH precursor suggests a topotactic crystallization of cobalt ferrite and yields phase pure spinel in unusual anisotropic platelet morphology. The preferred topotactic relationship in most particles is [111] ∥[001] . Due to the anion decomposition, holes are formed throughout the quasi monocrystalline platelets. This synthesis approach can be used for different ferrites and the unique microstructure leads to unusual chemical properties as shown by the application of the ex-LDH cobalt ferrite as catalyst in the selective oxidation of 2-propanol. Compared to commercial cobalt ferrite, which mainly catalyzes the oxidative dehydrogenation to acetone, the main reaction over the novel ex-LDH cobalt is dehydration to propene. Moreover, the oxygen evolution reaction (OER) activity of the ex-LDH catalyst was markedly higher compared to the commercial material.

Co3O4 nanospheres with a mean diameter of 19 nm were applied in the selective oxidation of 2-propanol to acetone in the gas phase. Compared with 9 nm spheres, the 19...

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The purpose of this study is to find a direct and quantitative correlation of the structure of Co 3−x Fe x O 4 nanoparticles with catalytic performance in 2-propanol oxidation. Eight nanocrystalline samples with varying iron contents are synthesized, and quantitative information regarding their structure is obtained from nitrogen physisorption, X-ray diffraction (XRD), X-ray absorption near-edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) analyzed by reverse Monte Carlo simulations. The catalytic performance is tested in 2-propanol oxidation in the gas phase. Overall, catalytic conversion data as a function of temperature are deconvoluted to obtain conversion and half-conversion temperatures as quantitative parameters for the different catalytic reaction channels. The crystal structure is described by a spinel structure with interstitial cation defects. These defects result in a reduced electronic state of the nanoparticles. The defect density depends on the cationic composition. We also observe a complex cationic distribution on tetrahedral and octahedral sites, which is strongly influenced by the overall cationic composition. In the catalytic tests, the samples exhibit a low-temperature pathway, which is deactivated in subsequent runs but can be recovered by an oxidative treatment of the catalyst. We find that the frequency of cation pairs Co O −Co O and Co O −Co T of the individual samples correlates directly to their catalytic activity and selectivity.

Holey hexagonal platelets of cobalt ferrite, CoFe2O4, can be obtained by co‐precipitation and thermal decomposition of a layered double hydroxide (LDH) precursor. These particles are single crystalline and porous at the same time and show a topotactic relationship with the precursor. They are active as catalyst in alcohol oxidation and as electrocatalyst in the oxygen evolution reaction showing a clearly different behavior than commercial powder likely due to their unique microstructure. For more details, see the Communcation by T. Lunkenbein, M. Behrens et al. on page 12443 ff.