Heterogenisation of a Carbonylation Catalyst on Dispersible Microporous Polymer Nanoparticles

The methanol carbonylation catalyst, cis-[Rh(CO)2I2]–, has been heterogenised within a dispersible microporous polymer support bearing cationic functionality. The microporous polymer has a core-shell structure in which the porous and insoluble...

Unprecedented Use of NHC Gold (I) Complexes as Catalysts for the Selective Oxidation of Ethane to Acetic Acid

The highly efficient eco-friendly synthesis of acetic acid (40% yield) directly from ethane is achieved by the unprecedented use of N-heterocyclic carbene (NHC) and N-heterocyclic oxo-carbene (NHOC) gold(I) catalysts in mild conditions. This is a selective and promising protocol to generate directly acetic acid from ethane, in comparison with the two most used methods: (i) the three-step, capital- and energy-intensive process based on the high-temperature conversion of methane to acetic acid; (ii) the current industrial methanol carbonylation processes, based in iridium and expensive rhodium catalysts. Green metrics determinations highlight the environmental advantages of the new ethane oxidation procedure. Comparison with previous reported published catalysts is performed to highlight the features of this remarkable protocol.

Sulfur Poisoning on Rh Nanoparticles but Sulfur Promotion on Its Single-Site Catalyst for Carbonylation

Sulfur poisoning is a challenge for most nanoparticle metal catalysts. A trace amount of sulfur contaminants could result in dramatic catalytic activity reduction or even irreversible deactivation1-5. Therefore, new approaches to enhance the catalyst sulfur-resistance have continuously attracted attention from academia and industry. Herein, a role reversal of sulfur from poison to promotor is presented for an Rh-based heterogeneous catalyst from supported Rh nanoparticles (NPs) to its single-site catalysts (Rh1/AC, AC: activated carbon) in methanol carbonylation, ethylene and acetylene hydrocarboxylic reaction with a feed containing 1000 ppm H2S (S-feed). In situ free-electron laser/time of flight mass spectrometry (In situ FEL/TOF MS) indicated that H2S could be quickly transformed into catalyst-friendly CH3SCH3 and/or CH3SH on the Rh1/AC, which coordinated with the Rh ions and promoted its methanol carbonylation reaction, possessing a lower energy barrier based on DFT calculations. On the contrary, strong adsorption of H2S on the surface of Rh NPs inhibited the reaction of reactants.

Heterogenisation of a Carbonylation Catalyst on Dispersible Microporous Polymer Nanoparticles

<div>The methanol carbonylation catalyst, <i>cis</i>-[Rh(CO)₂I₂]^–, has been heterogenised within a dispersible microporous polymer support bearing cationic functionality. The microporous polymer has a core-shell structure in which the porous and insoluble core (a co-polymer of divinylbenzene and 4-vinylpyridine) is suspended in solution by long hydrophilic poly(ethylene glycol) chains, allowing a stable suspension of the nanoparticles to form. Incorporation of 4-vinylpyridine as a co-monomer allows post-synthetic modification to generate <i>N</i>-methylpyridinium sites for electrostatic attachment of the anionic rhodium(I) complex. The dispersibility of the polymer-supported catalyst material facilitates the use of <i>in</i> <i>situ</i> transmission IR spectroscopy to obtain kinetic data for the oxidative addition of iodomethane to immobilised <i>cis</i>-[Rh(CO)₂I₂]^– (the rate-limiting step of the carbonylation cycle). Remarkably, the oxidative addition proceeds faster than for the homogeneous system (Bu₄N⁺ counter-ion, CH₂Cl₂, 25 °C). The polymer-supported catalyst was found to be active for methanol carbonylation, with a turnover frequency similar to that of the homogeneous analogue under the same conditions (10 bar CO, MeI/MeOH/CHCl₃, 120 °C). The supported catalyst is easily recovered and is shown to maintain comparable activity upon recycling.</div>

Heterogenisation of a Carbonylation Catalyst on Dispersible Microporous Polymer Nanoparticles

<div>The methanol carbonylation catalyst, <i>cis</i>-[Rh(CO)₂I₂]^–, has been heterogenised within a dispersible microporous polymer support bearing cationic functionality. The microporous polymer has a core-shell structure in which the porous and insoluble core (a co-polymer of divinylbenzene and 4-vinylpyridine) is suspended in solution by long hydrophilic poly(ethylene glycol) chains, allowing a stable suspension of the nanoparticles to form. Incorporation of 4-vinylpyridine as a co-monomer allows post-synthetic modification to generate <i>N</i>-methylpyridinium sites for electrostatic attachment of the anionic rhodium(I) complex. The dispersibility of the polymer-supported catalyst material facilitates the use of <i>in</i> <i>situ</i> transmission IR spectroscopy to obtain kinetic data for the oxidative addition of iodomethane to immobilised <i>cis</i>-[Rh(CO)₂I₂]^– (the rate-limiting step of the carbonylation cycle). Remarkably, the oxidative addition proceeds faster than for the homogeneous system (Bu₄N⁺ counter-ion, CH₂Cl₂, 25 °C). The polymer-supported catalyst was found to be active for methanol carbonylation, with a turnover frequency similar to that of the homogeneous analogue under the same conditions (10 bar CO, MeI/MeOH/CHCl₃, 120 °C). The supported catalyst is easily recovered and is shown to maintain comparable activity upon recycling.</div>