The sustainable utilization of methane is a major challenge for both science and industry. Methane is abundant in natural gas and biogas, yet its strong C–H bond and the high reactivity of methanol make selective conversion extremely difficult. Current industrial routes rely on multi-step processes, involving high-temperature methane reforming followed by high-pressure synthesis of methanol from syngas, resulting in a significant carbon footprint. Developing a direct and mild reaction pathway therefore strongly aligns with EU priorities such as the European Green Deal, REPowerEU, and the transition towards sustainable chemical production.
Originally, the project planned to explore praseodymium oxide and its mixed oxides for the direct conversion of methane to methanol (DCMM). Preliminary experiments, however, showed that praseodymium-based materials predominantly yield CO2 as the main product. This behaviour can be attributed to the intrinsically high oxygen reactivity of praseodymium oxides, which is difficult to modulate. Even the introduction of water is insufficient to suppress overly reactive surface oxygen species. These findings motivated a strategic shift towards ceria-based systems.
The oxygen species on ceria-based materials exhibit moderate activity, being neither overly reactive nor inert, which makes them well suited for selective oxidation reactions. Beyond pure ceria, mixed oxides such as Ce–ZrOₓ and Ce–LaOₓ offer opportunities to tune oxygen vacancy structures and surface oxygen species, enabling systematic exploration of structure–performance relationships for the direct conversion of methane to methanol. Previous studies have largely focused on ultra-high-vacuum model systems, leaving significant “pressure” and “materials” gaps relative to realistic catalytic environments.
This project aimed to bridge these gaps by integrating continuous-flow catalysis, advanced in situ and operando spectroscopy, and density functional theory (DFT). In addition to establishing ceria as a model oxide for partial methane oxidation, the project investigated Ce–ZrOₓ and Ce–LaOₓ mixed oxides to understand how compositional modification influences methane activation and methanol selectivity. The overall objectives were:
1.To determine the mechanisms of methane activation on ceria and ceria-based mixed oxide surfaces, and to clarify the roles of water and oxygen species under realistic reaction conditions.
2.To derive mechanistic principles linking surface composition, the nature and abundance of oxygen species and oxygen vacancies, thereby guiding the design of more active and selective oxide catalysts for the direct conversion of methane to methanol.
3.To develop transferable scientific insights that underpin the rational design and optimization of oxide catalysts for methane conversion under realistic operating conditions.
