Novel nanostructured catalysts with highly dispersed cobalt have been synthesized by the pyrolysis of metal phenanthroline complexes. Materials with significantly different properties were obtained ...by simply tuning the metal/ligand ratio. The catalytic potential of this class of compounds is shown by the first example of the dehydrogenation of formic acid under the catalysis of atomically dispersed cobalt. From TEM, XPS, and XRD characterization, KSCN poisoning, and acid leaching, the formation of CoNx species as the active site seems key to the success of this reaction. Excellent stability and recyclability make this new catalyst also attractive for other applications.
More efficient on their own: Atomically dispersed cobalt catalysts with excellent recyclability were developed for the dehydrogenation of formic acid (see picture). By tuning the metal/ligand ratio of the catalyst precursor, the structure of the heterogeneous material could be changed from nanoparticles to highly dispersed metal centers. Experimental results show the presence of CoNx species as the active sites.
The development of base metal catalysts for the synthesis of pharmaceutically relevant compounds remains an important goal of chemical research. Here, we report that cobalt nanoparticles encapsulated ...by a graphitic shell are broadly effective reductive amination catalysts. Their convenient and practical preparation entailed template assembly of cobalt-diamine-dicarboxylic acid metal organic frameworks on carbon and subsequent pyrolysis under inert atmosphere. The resulting stable and reusable catalysts were active for synthesis of primary, secondary, tertiary, and N-methylamines (more than 140 examples).The reaction couples easily accessible carbonyl compounds (aldehydes and ketones) with ammonia, amines, or nitro compounds, and molecular hydrogen under industrially viable and scalable conditions, offering cost-effective access to numerous amines, amino acid derivatives, and more complex drug targets.
Production of anilines—key intermediates for the fine chemical, agrochemical, and pharmaceutical industries—relies on precious metal catalysts that selectively hydrogenate aryl nitro groups in the ...presence of other easily reducible functionalities. Herein, we report convenient and stable iron oxide (Fe₂O₃)-based catalysts as a more earth-abundant alternative for this transformation. Pyrolysis of iron-phenanthroline complexes on carbon furnishes a unique structure in which the active Fe₂O₃ particles are surrounded by a nitrogen-doped carbon layer. Highly selective hydrogénation of numerous structurally diverse nitroarenes (more than 80 examples) proceeded in good to excellent yield under industrially viable conditions.
Hydrodehalogenation is a straightforward approach for detoxifications of harmful anthropogenic organohalide‐based pollutants, as well as removal of halide protecting groups used in multistep ...syntheses. A novel sustainable catalytic material was prepared from biowaste (chitosan) in combination with an earth‐abundant cobalt salt. The heterogeneous catalyst was fully characterized by transmission electron microscope, X‐ray diffraction, and X‐ray photoelectron spectroscopy measurements, and successfully applied to hydrodehalogenation of alkyl and (hetero)aryl halides with broad scope (>40 examples) and excellent chemoselectivity using molecular hydrogen as a reductant. The general usefulness of this method is demonstrated by successful detoxification of non‐degradable pesticides and fire retardants. Moreover, the potential of the catalyst as a deprotection tool is demonstrated in a multistep synthesis of (±)‐peronatin B (alkaloid).
One man's trash is another man's treasure: A sustainable heterogeneous catalyst was prepared from chitosan biomass and earth‐abundant cobalt salt. Using molecular hydrogen, the catalyst achieved hydrodehalogenation of a broad variety of organic halides (>40 examples) with excellent chemoselectivity; including harmful pesticides and a fire retardant.
Earth-abundant transition metal (Fe, Co, or Ni) and nitrogen-doped porous carbon electrocatalysts (M-N-C, where M denotes the metal) were synthesized from cheap precursors via silica-templated ...pyrolysis. The effect of the material composition and structure (i.e., porosity, nitrogen doping, metal identity, and oxygen functionalization) on the activity for the electrochemical CO2 reduction reaction (CO2RR) was investigated. The metal-free N-C exhibits a high selectivity but low activity for CO2RR. Incorporation of the Fe and Ni, but not Co, sites in the N-C material is able to significantly enhance the activity. The general selectivity order for CO2-to-CO conversion in water is found to be Ni > Fe ≫ Co with respect to the metal in M-N-C, while the activity follows Ni, Fe ≫ Co. Notably, the Ni-doped carbon exhibits a high selectivity with a faradaic efficiency of 93% for CO production. Tafel analysis shows a change of the rate-determining step as the metal overtakes the role of the nitrogen as the most active site. Recording the X-ray photoelectron spectra and extended X-ray absorption fine structure demonstrates that the metals are atomically dispersed in the carbon matrix, most likely coordinated to four nitrogen atoms and with carbon atoms serving as a second coordination shell. Presumably, the carbon atoms in the second coordination shell of the metal sites in M-N-C significantly affect the CO2RR activity because the opposite reactivity order is found for carbon supported metal meso-tetraphenylporphyrin complexes. From a better understanding of the relationship between the CO2RR activity and the material structure, it becomes possible to rationally design high-performance porous carbon electrocatalysts involving earth-abundant metals for CO2 valorization.
A general epoxidation of aromatic and aliphatic olefins has been developed under mild conditions using heterogeneous CoxOy–N/C (x=1,3; y=1,4) catalysts and tert‐butyl hydroperoxide as the terminal ...oxidant. Various stilbenes and aliphatic alkenes, including renewable olefins, and vitamin and cholesterol derivatives, were successfully transformed into the corresponding epoxides with high selectivity and often good yields. The cobalt oxide catalyst can be recycled up to five times without significant loss of activity or change in structure. Characterization of the catalyst by XRD, TEM, XPS, and EPR analysis revealed the formation of cobalt oxide nanoparticles with varying size (Co3O4 with some CoO) and very few large particles with a metallic Co core and an oxidic shell. During the pyrolysis process the nitrogen ligand forms graphene‐type layers, in which selected carbon atoms are substituted by nitrogen.
A general epoxidation of aromatic and aliphatic olefins under mild conditions using recyclable heterogeneous CoxOy–N/C (x=1,3; y=1,4) catalysts and tert‐butyl hydroperoxide as the terminal oxidant has been developed. Various stilbenes and aliphatic alkenes were successfully transformed into the corresponding epoxides with high selectivity and good yields.
Abstract
Due to the complexity of heterogeneous catalysts, identification of active sites and the ways for their experimental design are not inherently straightforward but important for tailored ...catalyst preparation. The present study reveals the active sites for efficient C–H bond activation in C
1
–C
4
alkanes over ZrO
2
free of any metals or metal oxides usually catalysing this reaction. Quantum chemical calculations suggest that two Zr cations located at an oxygen vacancy are responsible for the homolytic C–H bond dissociation. This pathway differs from that reported for other metal oxides used for alkane activation, where metal cation and neighbouring lattice oxygen form the active site. The concentration of anion vacancies in ZrO
2
can be controlled through adjusting the crystallite size. Accordingly designed ZrO
2
shows industrially relevant activity and durability in non-oxidative propane dehydrogenation and performs superior to state-of-the-art catalysts possessing Pt, CrO
x
, GaO
x
or VO
x
species.
Molecularly well-defined homogeneous catalysts are known for a wide variety of chemical transformations. The effect of small changes in molecular structure can be studied in detail and used to ...optimize many processes. However, many industrial processes require heterogeneous catalysts because of their stability, ease of separation and recyclability, but these are more difficult to control on a molecular level. Here, we describe the conversion of homogeneous cobalt complexes into heterogeneous cobalt oxide catalysts via immobilization and pyrolysis on activated carbon. The catalysts thus produced are useful for the industrially important reduction of nitroarenes to anilines. The ligand indirectly controls the selectivity and activity of the recyclable catalyst and catalyst optimization can be performed at the level of the solution-phase precursor before conversion into the active heterogeneous catalyst.
Amines represent important intermediates in chemical and biological processes. Herein, we describe the use of a nanostructured iron‐based catalyst for the tandem reductive amination between ...nitroarenes and aldehydes using hydrogen as reductant. The nanostructured iron‐catalyst is prepared by immobilization of an iron–phenanthroline complex onto a commercially available carbon support. In the reaction sequence a primary amine is formed in situ from the corresponding nitro compound. Reversible condensation with aldehydes forms the respective imines, which are finally reduced to the desired secondary amine. This synthesis of secondary amines is atom‐economical and environmentally attractive using cheap and readily available organic compounds as starting materials.
A well‐defined carbon‐supported iron‐based catalyst is investigated for a one‐pot multistep synthesis of secondary amines. The reductive amination of aldehydes includes the industrially relevant hydrogenation of nitroarenes to functionalized anilines as well as the conclusive reduction of the formed Schiff base. The catalytic activity of this cheap, promising catalyst is caused by a core–shell‐structured iron oxide nanocomposite, which is encapsulated by individually nitrogen‐enriched graphene‐type layers.
The development of efficient and selective nanostructured catalysts for industrially relevant hydrogenation reactions continues to be an actual goal of chemical research. In particular, the ...hydrogenation of nitriles and nitroarenes is of importance for the production of primary amines, which constitute essential feedstocks and key intermediates for advanced chemicals, life science molecules and materials. Herein, we report the preparation of graphene shell encapsulated Co
O
- and Co-nanoparticles supported on carbon by the template synthesis of cobalt-terephthalic acid MOF on carbon and subsequent pyrolysis. The resulting nanoparticles create stable and reusable catalysts for selective hydrogenation of functionalized and structurally diverse aromatic, heterocyclic and aliphatic nitriles, and as well as nitro compounds to primary amines (>65 examples). The synthetic and practical utility of this novel non-noble metal-based hydrogenation protocol is demonstrated by upscaling several reactions to multigram-scale and recycling of the catalyst.
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