Methane, the predominant constituent of natural and shale gas, is often flared for heating. Despite its significant potential as a carbon source for chemical synthesis, its inherent chemical inertness poses substantial hurdles for the efficient conversion. Traditional industrial processes for methane conversion are conducted via syngas at high temperature and pressure, being highly energy-intensive and leading to multi-products.

 The prospect of directing partial oxidization of methane to liquid oxygenates under relatively mild conditions has garnered huge attention in the recent past as it is a sustainable alternative to the current chemical industry. However, achieving a high conversion rate and high selectivity towards a specific target product has proven to be a formidable task. This challenge is further exacerbated when targeting more valuable products that necessitate carbon-carbon (C-C) coupling, which explains the predominance of C1 oxygenates, particularly methanol, in the reported selective partial methane oxidation processes to date.

 From a practical standpoint, the selective conversion of methane to a specific C₂₊ chemical, such as ethanol, holds considerable appeal. However, the requisite C-C coupling introduces a series of scientific challenges. The catalytic microenvironment must be capable of: i) providing sufficient charge separation and delocalization to drive a specific redox pathway; ii) coordinating the binding of methane molecules, co-reactants, and reaction intermediates in close proximity; and iii) facilitating the rapid desorption of the thermodynamically unstable product to prevent overoxidation.

 Based on these understandings, our group members from University College London and Tsinghua University effectively collaborate with scientists from Cardiff University, Hong Kong University and University of Science and Technology of China to develop a new concept of intramolecular junction for methane conversion to the C₂ oxygenate ethanol. With nearly 10 years’ hard work of four phd students and three postdoctoral researchers, a breakthrough of the methane conversion has been achieved. The key component of new findings is the design of unique junction architecture in a CTF-1 polymer molecule, which is composed of alternate benzene and triazine units. One benzene unit and the neighbor triazine unit form the intramolecular junction, with the former unit for electrons and the latter for holes accumulation. Such architecture can facilitate efficient and long-lived charges separation after their generation, while also enables preferential adsorption of O₂ and H₂O to the benzene and triazine units, respectively. This dual-site feature further effectively separates the C-C coupling sites from hydroxyl radicals formation sites, thereby mitigating the risk of overoxidation of the intermediate. When further enhanced with the addition of Pt, the intramolecular junction photocatalyst presents a good ethanol production rate with a high selectivity of ca. 80% and a methane conversion rate of 2.3% in a single run in a packed-bed flow reactor, leading to an apparent quantum efficiency of 9.4%.

 We anticipate that the further exploration of the new concept of "intramolecular junction" will lead to the development of even more efficient and selective catalysts for C-C coupling reactions. The applications of this concept are not limited to methane conversion but also hold potential for long chain alkane conversion, opening new avenues for sustainable chemical synthesis and the utilization of abundant organic carbon resources. In addition the technology also holds significant promise for the high-value conversion of distributed methane sources, such as oilfield byproduct gas and particularly being beneficial in rural locations where the capture and utilization of methane can lead to a reduction in greenhouse gas emissions and the production of valuable chemicals on-site.