Single-atom Ru coupled with AlCl₃ to promote asymmetric C-C coupling between CH₄ and CO₂.

Abstract

Direct synthesis of acetic acid from CH₄ and CO₂ offers a sustainable strategy to utilize these byproducts co-existed in many anthropogenic scenarios with 100% atom efficiency and mitigate greenhouse effect. But this reaction remains a grand challenge due to chemical inertness of two reactants and sluggish kinetics of C-C coupling. Herein, we propose a bifunctional catalyst design, consisted of metal and Lewis acid, to activate CH₄ and CO₂ via nucleophilic and electrophilic attacks, respectively, which generating two intermediates with opposite electron properties and promote asymmetric C-C coupling. To achieve this, a rational design with "six-step" screening predicts an efficient catalyst, i.e., Keggin-type phosphotungstic acid supporting equimolar single-atom ruthenium and aluminum chloride. Then we synthesize and demonstrate this catalyst with the activity with TOF of 19.3 h^-1 and acetic acid selectivity of 95.7%. In situ infrared spectroscopy and theoretical studies reveal a Langmuir-Hinshelwood mechanism for C-C coupling with a low barrier of 14.03 kcal mol^-1. Specifically, CO₂ activation by AlCl₃ via S_E2 process yields a positively charged state, which readily interacts with the negatively charged *CH₃ from CH₄ activation.