Elena Rozhko

Azine‐Linked Covalent Organic Framework (COF)‐Based Mixed‐Matrix Membranes for CO2/CH4 Separation

Mixed-matrix membranes (MMMs) comprising Matrimid and a microporous azine-linked covalent organic frameworks (ACOF-1) were prepared and tested in the separation of CO2 from an equimolar CO2 /CH4 mixture. The COF-based MMMs show a more than doubling of the CO2 permeability upon 16 wt % ACOF-1 loading together with a slight increase in selectivity compared to the bare polymer. These results show the potential of COFs in the preparation of MMMs.

Shaping Covalent Triazine Frameworks for the Hydrogenation of Carbon Dioxide to Formic Acid

A facile one‐step method to shape covalent triazine frameworks (CTFs) for catalytic applications is reported. Phase inversion of the CTF powder by using a polyimide as a binder in a microfluidic device results in the formation of composite spheres with accessible CTF porosity and a high mechanical and thermal stability. The fabricated spheres can be used to host organometallic complexes. The obtained shaped catalysts, Ir@CTF spheres, are active and fully recyclable in the direct hydrogenation of carbon dioxide into formic acid under mild reaction conditions (20 bar and 50–90 °C) and in the dehydrogenation of formic acid.

Oxidation of 1,2-Cyclohexanediol to Adipic Acid with Oxygen: A Study Into Selectivity-Affecting Parameters

The aerobic oxidation of trans‐1,2‐cyclohexanediol in the synthesis of adipic acid was studied. Two classes of catalysts are compared, 1) alumina‐supported Ru(OH)3, and 2) Keggin type P/Mo/V polyoxometalates. These two classes are representative examples because they are active in alcohol oxidation under quite different reaction conditions. In the former case, basic conditions are needed in order to activate the substrate, whereas with polyoxometalates, acidic conditions are used. Their catalytic behavior showed remarkable differences; in basic conditions, the reaction network was very complex, and several side reactions led to a number of by‐products, with a low selectivity to adipic acid in the end. The supported Ru(OH)3 catalyst was very efficient in 1,2‐cyclohexanediol oxidative dehydrogenation to 1,2‐cyclohexanedione, but several undesired reactions occurred starting from this key intermediate under basic conditions: rearrangement into 6‐hydroxycaprolactone and 1‐hydroxycyclopentanecarboxylic acid, and formation of the product of aldol condensation. The former compound was also an intermediate for adipic acid formation, but this reaction gave only a minor contribution to the reactant conversion. Polyoxometalates were extremely selective in 1,2‐cyclohexanediol conversion into adipic acid, but under acidic conditions the product reacted with the unconverted reactant to yield the corresponding ester.

Metal–Organic Framework Mediated Cobalt/Nitrogen‐Doped Carbon Hybrids as Efficient and Chemoselective Catalysts for the Hydrogenation of Nitroarenes

A Co@N‐doped carbon (Co@NC) hybrid was synthesized by thermal decomposition of the metal–organic framework (MOF) ZIF‐67 under N2 atmosphere. These hybrid materials exhibit outstanding catalytic activity and chemoselectivity for the conversion of a wide range of substituted nitroarenes to their corresponding anilines under relatively mild reaction conditions. The high catalytic performance is attributed to the formation of cobalt nanoparticles and to the presence of atomically dispersed Co species in close interaction with nitrogen‐doped graphene. Both active species are formed in situ during the pyrolytic transformation of ZIF‐67. The catalysts could be reused in consecutive runs, exhibiting a slightly lower activity ascribed to blockage of the active sites by strongly adsorbed reaction species. These results open up a pathway for the design of noble‐metal‐free solid catalysts for industrial applications.

Dynamic Release–Immobilization of a Homogeneous Rhodium Hydroformylation Catalyst by a Polyoxometalate Metal–Organic Framework Composite

Thermal treatment of phosphotungstic acid (PTA)‐MIL‐101(Cr) composites in the presence of hydroformylation catalyst RhH(CO)(PPh3)3 leads to immobilization of the homogeneous Rh complex within the metal–organic framework (MOF) scaffold by coordination of PTA‐Rh. The Rh complex‐containing MOFs are tested in the hydroformylation of 1‐octene in which PTA competes with CO during ligand association. In the presence of the carbonyl ligand, the Rh complex is released from the MOF and behaves as a homogeneous catalyst. Therefore, the product spectra and selectivities of the Rh complex‐containing MOFs are similar to those of RhH(CO)(PPh3)3. Upon CO evacuation, Rh recoordinates to PTA, allowing for easy recycling of this new pseudo‐heterogeneous catalyst.

Revising the Role of a Dioxirane as an Intermediate in the Uncatalyzed Hydroperoxidation of Cyclohexanone in Water

The mechanism of the oxidation of cyclohexanone with an aqueous solution of hydrogen peroxide has been investigated. Experiments revealed the preliminary formation of an intermediate, identified as cyclohexylidene dioxirane, in equilibrium with the ketone, followed by formation of 1-hydroperoxycyclohexanol (Criegee adduct). Computational analysis with explicit inclusion of up to two water molecules rationalized the formation of the dioxirane intermediate via addition of the hydroperoxide anion to the ketone and revealed that this species is not involved in the formation of the Criegee adduct. The direct addition of hydrogen peroxide to the ketone is predicted to be favored over hydrolysis of the dioxirane, the latter in competition with ring opening to carbonyl oxide followed by hydration. However, dioxirane may account for the formation of the bis-hydroperoxide derivative.