Researchers are paving the way for greener energy conversions with their latest development—a highly efficient catalyst for directly transforming methane (CH4) to acetic acid (CH3COOH). By employing MoS2-confined Rh-Zn atomic pairs integrated with TiO2, this novel photo-driven carbonylation process achieves remarkable selectivity and productivity, marking significant advancements in sustainable energy practices.
The ability to convert methane, one of the most abundant hydrocarbons, to valuable chemicals like acetic acid is of immense practical importance. Methane is primarily used as fuel; utilizing it as a feedstock for chemicals offers possibilities for reducing emissions and increasing value from natural gas sources. This recent study has demonstrated how the new catalyst can directly convert methane, carbon monoxide (CO), and oxygen (O2) under mild conditions without requiring additional energy input, unlike traditional methods.
The team’s research shows impressive metrics, achieving CH3COOH productivity of 152.0 µmol gcat−1 h−1, and turnover frequency (TOF) of 62.0 h−1, with selectivity reaching 96.5%, outperforming earlier photocatalytic approaches. This success can largely be attributed to the unique design of the Rh-Zn pairs confined within the MoS2 lattice, which enhances the catalytic synergy.
Historically, converting methane to multi-carbon oxygenates has posed challenges due to the high stability of methane's C–H bonds and the need for selective chemical pathways. This new process simplifies the reaction steps significantly, relying on direct carbonylation to convert methane to acetic acid. The introduction of carbon monoxide allows for the bypass of previously required intermediate stages, which often resulted in unwanted side reactions and lower yields.
The catalyst operates through several key steps, beginning with the activation and dissociation of O2 to generate reactive oxygen species. Following this, CH4 is dissociated to form CH3 species on the Zn site, which then couples with CO adsorbed on the adjacent Rh site to form the key CH3CO intermediate. This innovative mechanism, confirmed by systematic experimental and computational investigations, clearly highlights how the confined dual-site nature of Rh-Zn enhances performance.
The photo-excited electrons from TiO2 play a fundamental role, promoting oxygen reduction and facilitating CH4 activation by generating highly reactive OH species. This discovery not only breaks the trade-off between activity and selectivity observed with previous methodologies but sets the stage for future explorations of such dual-site catalysts.
The researchers conducted its tests using advanced spectroscopic techniques, proving the importance of the specific atomic configurations within the catalyst. By carefully examining the respective roles of each component, they were able to ascertain the impact of dual co-catalysts—and how they operate at the molecular level, guiding improvements for sustainable chemical production.
With the catalyst exhibiting good stability over successive cycles without significant deactivation, it could be viable for industrial applications. The methodology demonstrates promise not just for methane conversion, but also sets precedents for leveraging similar strategies across other chemical transformations.
Overall, this work stands as a substantial contribution to catalysis science, aligning with global efforts to transition toward sustainable energy sources through innovative chemical processes. The advancements achieved by such catalysts could lead to significant environmental benefits, promoting cleaner and more efficient production methods for valuable chemical resources.