Carsten Kreyenschulte

Stable and Inert Cobalt Catalysts for Highly Selective and Practical Hydrogenation of C≡N and C═O Bonds

Novel heterogeneous cobalt-based catalysts have been prepared by pyrolysis of cobalt complexes with nitrogen ligands on different inorganic supports. The activity and selectivity of the resulting materials in the hydrogenation of nitriles and carbonyl compounds is strongly influenced by the modification of the support and the nitrogen-containing ligand. The optimal catalyst system ([Co(OAc)2/Phen@α-Al2O3]-800 = Cat. E) allows for efficient reduction of both aromatic and aliphatic nitriles including industrially relevant dinitriles to primary amines under mild conditions. The generality and practicability of this system is further demonstrated in the hydrogenation of diverse aliphatic, aromatic, and heterocyclic ketones as well as aldehydes, which are readily reduced to the corresponding alcohols.

Highly selective hydrogenation of arenes using nanostructured ruthenium catalysts modified with a carbon–nitrogen matrix

Selective hydrogenations of (hetero)arenes represent essential processes in the chemical industry, especially for the production of polymer intermediates and a multitude of fine chemicals. Herein, we describe a new type of well-dispersed Ru nanoparticles supported on a nitrogen-doped carbon material obtained from ruthenium chloride and dicyanamide in a facile and scalable method. These novel catalysts are stable and display both excellent activity and selectivity in the hydrogenation of aromatic ethers, phenols as well as other functionalized substrates to the corresponding alicyclic reaction products. Furthermore, reduction of the aromatic core is preferred over hydrogenolysis of the C–O bond in the case of ether substrates. The selective hydrogenation of biomass-derived arenes, such as lignin building blocks, plays a pivotal role in the exploitation of novel sustainable feedstocks for chemical production and represents a notoriously difficult transformation up to now.

Synthesis of Single Atom Based Heterogeneous Platinum Catalysts: High Selectivity and Activity for Hydrosilylation Reactions

Catalytic hydrosilylation represents a straightforward and atom-efficient methodology for the creation of C–Si bonds. In general, the application of homogeneous platinum complexes prevails in industry and academia. Herein, we describe the first heterogeneous single atom catalysts (SACs), which are conveniently prepared by decorating alumina nanorods with platinum atoms. The resulting stable material efficiently catalyzes hydrosilylation of industrially relevant olefins with high TON (≈105). A variety of substrates is selectively hydrosilylated including compounds with sensitive reducible and other functional groups (N, B, F, Cl). The single atom based catalyst shows significantly higher activity compared to related Pt nanoparticles.

Pd-Supported on N-doped carbon: improved heterogeneous catalyst for base-free alkoxycarbonylation of aryl iodides

Novel Pd-based heterogeneous catalysts were prepared through immobilization of Pd(OAc)2/phenanthroline on carbon and subsequent pyrolysis. The most active catalyst was characterized by TEM, XPS and XRD techniques and was successfully used for the base-free methoxycarbonylation of aryl iodides. Notably, no metal contamination (detection limit < 0.5 ppm) in the final products was observed.

H2 Generation with (Mixed) Plasmonic Cu/Au-TiO2 Photocatalysts: Structure–Reactivity Relationships Assessed by in situ Spectroscopy

Monometallic Cu and bimetallic Cu/Au‐TiO2 catalysts were prepared by impregnation (IM) and reductive precipitation (RP) methods in sequential (SP) and simultaneous mode (CP) and tested for photocatalytic H2 generation from H2O/methanol mixtures with visible (400–700 nm) and UV/Vis light (320–500 nm). Comprehensive studies by high‐resolution (HR)‐STEM, X‐ray photoelectron spectroscopy (XPS), and different in situ methods (X‐ray absorption near‐edge structure (XANES), UV/Vis, and EPR spectroscopy) revealed that IM leads to dispersed surface Cu species with no clear particle formation, which is poorly active under visible light, whereas plasmonic Cu0 nanoparticles formed by RP are about three times more active under the same conditions. In Cu/Au‐TiO2 catalysts prepared by RP‐SP, highly dispersed Cu surface species boost H2 production under UV/Vis light, owing to the effective separation within TiO2 and electron trapping by Cu, whereas small Cu0 and Au0 particles remain widely separated. When Cu/Au‐TiO2 catalysts are prepared by RP‐CP, mixed Cu/Au particles of uniform size (4–8 nm) provide the highest H2 evolution rates under visible light, owing to effective surface plasmon resonance absorption.

Probing the structural changes and redox behavior of mixed molybdate catalysts under ammoxidation conditions: an operando Raman spectroscopy study

Mixed model molybdate catalysts that contain CoMoO4, Bi2Mo3O12, and Fe2Mo3O12 were investigated in the ammoxidation reaction of propene to acrylonitrile to study the redox behavior of the iron molybdate component. The flexible changes of the oxidation state of the Fe component during ammoxidation were followed by examining the intensity changes of the characteristic bands of Fe2Mo3O12 and FeMoO4 in the Raman spectra and could be correlated with the catalyst performance examined by simultaneous MS analysis. Depending on the catalyst composition and the oxygen content in the feed, Fe2Mo3O12 is reduced to a different extent, and consequently, FeMoO4 is formed, which is accompanied by a restructuring of the catalyst and the formation of nanostructured MoOx species. In accordance with previous investigations, operando Raman studies revealed that CoMoO4 and Bi2Mo3O12 influence the redox behavior of Fe2Mo3O12 in different ways.

Synthesis of cobalt nanoparticles by pyrolysis of vitamin B12: a non-noble-metal catalyst for efficient hydrogenation of nitriles

A facile preparation of vitamin B12-derived carbonaceous cobalt particles supported on ceria is reported. The resulting composite material is obtained upon wet impregnation of ceria with natural cyanocobalamin and consecutive pyrolysis under inert conditions. The novel catalyst shows good to excellent performance in the industrially relevant heterogeneous hydrogenation of nitriles to the corresponding primary amines.

Hydrogenation of terminal and internal olefins using a biowaste-derived heterogeneous cobalt catalyst

An active and renewable catalyst for olefin hydrogenation was obtained by inclusion of cobalt in a carbon matrix derived from the pyrolysis of chitosan. Hydrogenation of olefins is achieved using biowaste-derived cobalt chitosan catalysts. Characterization of the optimal Co@Chitosan-700 by STEM (scanning transmission electron microscopy), EELS (electron energy loss spectroscopy), PXRD (powder x-ray diffraction), and elemental analysis revealed the formation of a distinctive magnetic composite material with high metallic Co content. The general performance of this catalyst is demonstrated in the hydrogenation of 50 olefins including terminal, internal, and functionalized derivatives, as well as renewables. Using this nonnoble metal composite, hydrogenation of terminal C==C double bonds occurs under very mild and benign conditions (water or methanol, 40° to 60°C). The utility of Co@Chitosan-700 is showcased for efficient hydrogenation of the industrially relevant examples diisobutene, fatty acids, and their triglycerides. Because of the magnetic behavior of this material and water as solvent, product separation and recycling of the catalyst are straightforward.