Direct Formation of C₃ Oxygenates through Photocatalytic CH₄-CO Coupling

Multicarbon (C_n, where n ≥ 2) oxygenates are important industrial precursors that can be synthesized from the coupling of simple and abundant C₁ feedstock such as CH₄. While C₂ products from this route have been reported, those involving the direct coupling of more than two C₁ precursors are rare. As a proof of concept, here we report the synthesis of acetone (CH₃COCH₃) through the direct coupling of two CH₄ and one CO using a combined photothermocatalytic approach. With TiO₂ as a light absorber and Pd nanoparticle as a cocatalyst, CH₄ activation and subsequent coupling with CO were achieved at 10 bar and 150 °C. A high selectivity of acetone formation among all liquid products (>80%) was measured. Experiments with isotope-labeled precursors confirmed that the product was a result of the direct coupling of CH₄ and CO. The other major liquid product was acetic acid (CH₃COOH), which was a result of a single coupling between CH₄ and CO. The suitable binding strength between Pd and the reactive intermediates was proposed as a key reason for the high selectivity toward C₃ products.