Synthesis of acetic acid from CO2, CH3I and H2 using a water-soluble electron storage catalyst

Storing electrons from H2 for transfer to CO2, all at room temperature

We present an Ir complex that extracts electrons from H2 at room temperature and stores them as a H2-derived energy carrier (H2EC) at room temperature. Furthermore, we demonstrate that this complex reduces CO2 to a metal-CO22- species at room temperature, and present the first electrospray ionisation mass spectrum for this compound.

Aqueous phase conversion of CO2 into acetic acid over thermally transformed MIL-88B catalyst

Sustainable production of acetic acid is a high priority due to its high global manufacturing capacity and numerous applications. Currently, it is predominantly synthesized via carbonylation of methanol, in which both the reactants are fossil-derived. Carbon dioxide transformation into acetic acid is highly desirable to achieve net zero carbon emissions, but significant challenges remain to achieve this efficiently. Herein, we report a heterogeneous catalyst, thermally transformed MIL-88B with Fe⁰ and Fe₃O₄ dual active sites, for highly selective acetic acid formation via methanol hydrocarboxylation. ReaxFF molecular simulation, and X-ray characterisation results show a thermally transformed MIL-88B catalyst consisting of highly dispersed Fe⁰/Fe(II)-oxide nanoparticles in a carbonaceous matrix. This efficient catalyst showed a high acetic acid yield (590.1 mmol/g_cat.L) with 81.7% selectivity at 150 °C in the aqueous phase using LiI as a co-catalyst. Here we present a plausible reaction pathway for acetic acid formation reaction via a formic acid intermediate. No significant difference in acetic acid yield and selectivity were noticed during the catalyst recycling study up to five cycles. This work is scalable and industrially relevant for carbon dioxide utilisation to reduce carbon emissions, especially when green methanol and green hydrogen are readily available in future.

Safe, One-Pot, Homogeneous Direct Synthesis of H2O2

Hydrogen peroxide is an environmentally friendly oxidizing agent but current synthetic methods are wasteful. This is a result of the high flammability of H₂/O₂ mixtures and/or the requirement for cocatalysts. In this paper, we report the synthesis of H₂O₂ by means of a homogeneous catalyst, which allows a safe, one-pot synthesis in water, using only H₂ and O₂. This catalyst is capable of removing electrons from H₂, storing them for the reduction of O₂, and then permitting the protonation of the reduced oxygen to H₂O₂. The turnover number (TON) is 910 under an H₂/O₂ (95/5) atmosphere (1.9 MPa) for 12 h at 23 °C, which is the highest of any homogeneous catalyst. Furthermore, we propose a reaction mechanism based on two crystal structures.

Reductive C(sp3)-C(sp3) homo-coupling of benzyl or allyl halides with H2 using a water-soluble electron storage catalyst

This paper reports the first example of a reductive C(sp3)-C(sp3) homo-coupling of benzyl/allyl halides in aqueous solution by using H2 as an electron source {turnover numbers (TONs) = 0.5-2.3 for 12 h}. This homo-coupling reaction, promoted by visible light, is catalysed by a water-soluble electron storage catalyst (ESC). The reaction mechanism, and four requirements to make it possible, are also described.

C-H Arylation of Benzene with Aryl Halides using H2 and a Water-Soluble Rh-Based Electron Storage Catalyst

This paper reports the first example of C-H arylation of benzene under mild conditions, using H₂ as an electron source {turnover numbers (TONs)=0.7-2.0 for 24 h}. The reaction depends on a Rh-based electron storage catalyst, and proceeds at room temperature and in aqueous solution. Furthermore, the H₂ is inactive during the radical transfer step, greatly reducing unwanted side reactions.