First Author: Xie Jiajia
Corresponding Authors: Huang Weixin, Guo Zhengxiao, C. Richard A. Catlow, Tang Junwang
Affiliations: University College London, University of Science and Technology of China, Cardiff University, University of Hong Kong, Tsinghua University
Paper DOI: 10.1038/s41586-025-08630-x
The team led by Academician Tang Junwang from Tsinghua University, in collaboration with Professor Huang Weixin's team from the University of Science and Technology of China, Academician C. Richard A. Catlow's team from Cardiff University, and Professor Guo Zhengxiao's team from the University of Hong Kong, has proposed the concept of intramolecular junction for the first time. They confirmed that the CTF-1 material with the intramolecular junction effect can promote the spatial separation of photogenerated electron-hole pairs. The sites enriched with photogenerated holes facilitate the activation of methane molecules, while the activated methyl species migrate to the regions enriched with photogenerated electrons, thereby spatially separating methane activation, methyl coupling, and oxygen reduction, which inhibits the excessive oxidation of methyl and enhances the selectivity of C-C coupling products.
Figure 1 Schematic Diagram of Photocatalytic Oxidation of Methane using CTF-1
In the global energy landscape, with the continuous rise in demand for clean energy and high-value chemicals, the efficient conversion of methane has become a key research topic in the field of chemistry. Methane, as the main component of natural gas and shale gas, is abundant as a carbon source with great potential in chemical synthesis. However, the high stability of methane molecules presents significant challenges during conversion. Traditional conversion methods often struggle to achieve both high conversion rates and high selectivity for target products under mild conditions, especially when generating high-value products like ethanol that require C-C coupling, which poses even greater challenges.
Although traditional thermocatalytic technologies play an important role in chemical production, they have inherent limitations in the selective conversion of methane. The high temperature and high pressure reaction conditions lead to excessive molecular thermal motion, resulting in complex and diverse reaction pathways with a large number of by-products, severely affecting the selectivity and yield of target products. For example, in the traditional thermocatalytic process of oxidizing methane to produce methanol or other products, various hydrocarbons and oxygen-containing compounds are often generated, making it difficult to achieve efficient synthesis of a single high-value product.
In stark contrast, photocatalytic technology can effectively regulate the catalyst's absorption and conversion efficiency of specific wavelength light by adjusting its elemental composition, crystal structure, and surface morphology, thereby controlling the generation and separation of photogenerated charge carriers. This allows reactant molecules to be activated under relatively mild conditions, avoiding the excessive activation issues caused by high temperature and pressure in traditional thermocatalysis, thus providing significant advantages in the activation and selective conversion of highly stable molecules.
Over the past 10 years, Academician Tang's research group has selectively converted methane into methanol (Nat Catal 1, 889–896, 2018, Nat Commun 13, 2930, 2022), formaldehyde (Nat Sustain 7, 1171–1181, 2024, Nat Commun 14, 2690, 2023), and ethane (Nat Energy 8, 1013–1022, 2023, Nat Commun 14, 6343, 2023, Nat Commun 15, 7535, 2024, Angew. Chem. Int. Ed., 59, 19702–19707, 2020) using photocatalytic technology. This has laid the foundation for further exploration of the efficient and highly selective conversion of methane into higher value-added products driven by photocatalysis.
1. Innovative catalyst design: The concept of intramolecular junction is proposed for the first time, applying the CTF-1 catalyst with alternating phenyl and triazine units. This unique structure effectively separates photogenerated electron-hole pairs, providing a favorable microenvironment for C-C coupling.
2. High selectivity and conversion rate: Under appropriate conditions, the selectivity of CTF-1 for converting methane to ethanol can reach approximately 80%, with a high conversion rate. After loading with Pt, the apparent quantum efficiency increases to 9.4%.
3. In-depth exploration of reaction mechanisms: A combination of advanced characterization techniques, theoretical calculations, and isotope labeling experiments was used to detail the reaction pathway for the conversion of methane to ethanol, including the roles of oxygen, especially water, the formation and transformation of intermediates, and the explanation of product selectivity mechanisms.
4. Good stability performance: CTF-1 shows good stability over long reaction times (50 h), maintaining its structure and activity.
CTF-1 is a covalent triazine-based framework material characterized by an intramolecular junction composed of alternating triazine and phenyl units. Theoretical calculations reveal that the triazine units in CTF-1 can accumulate photogenerated holes, which can directly or indirectly activate the C-H bonds of methane to form methyl radicals; meanwhile, the phenyl units not only facilitate the efficient separation and accumulation of photogenerated electrons but also provide the most favorable adsorption sites for methyl radicals, promoting their coupling on the phenyl ring. This intramolecular junction theoretically creates favorable conditions for C-C coupling, allowing newly formed methyl species to migrate to the phenyl units for coupling, thus avoiding further oxidation by photogenerated holes on the triazine units. Concurrently, oxygen is reduced on the phenyl ring, further reacting with ethane to produce ethanol.
In a packed bed photocatalytic reactor, methane activation experiments using CTF-1 revealed that the presence of both water and oxygen significantly increased ethanol production, highlighting the critical role of water and oxygen in the reaction. Compared to typical inorganic photocatalysts TiO2 and polymeric catalyst g-C3N4, CTF-1 demonstrated significant advantages in both activity and selectivity. Under the same conditions on TiO2, only CO2 is produced, while g-C3N4 can convert methane to ethanol but with lower yield and selectivity. The amount of ethanol produced by CTF-1 is five times that of g-C3N4, achieving a selectivity of 79%. To further enhance activity, CTF-1 was modified with Pt, and results indicated that the introduction of 3wt% PtOx increased ethanol yield by nearly 50%, while maintaining about 80% selectivity.
To clarify the reaction mechanism and the carbon source in the products, isotope labeling experiments were conducted. When using 13CH4, the mass spectrum peaks of ethanol products showed corresponding shifts, and no fragments related to 12C ethanol were detected, providing strong evidence that the carbon source of ethanol comes from methane rather than the catalyst. Experiments using 18O-labeled water indicated that the oxygen atoms in ethanol come from O2, while the oxygen source for CO2 primarily comes from the OH radicals generated by the reaction of water with methane, with a small portion coming from O2. Gas adsorption analysis showed that water does not compete with methane for adsorption, and the amount of water adsorbed is greater. DFT calculations indicate that water can react with photogenerated holes to hydroxylate the catalyst surface, lowering the activation energy for methyl radical formation, thus promoting methane activation. Further studies revealed that on CTF-1, methane first converts to ethane intermediates, which then further converts to ethanol on the phenyl ring in the presence of O2. The differences in adsorption energy of CTF-1 for ethanol and methanol, along with the tendency of methanol to undergo excessive oxidation, collectively contribute to the high selectivity of CTF-1 for ethanol.
NEXAFS studies show that CTF-1 effectively separates photogenerated electrons and holes under illumination, accumulating in the phenyl and triazine units respectively. This corresponds with the lower photoluminescence (PL) intensity, indicating a low charge recombination rate, which is beneficial for improving methane conversion rates. DRIFTS spectra reveal that the adsorption of water on CTF-1 differs from TiO2 and g-C3N4, primarily consisting of free water molecules, while DFT calculations further determine the adsorption sites and modes of water on CTF-1. EPR confirms that CTF-1's ability to activate water to generate ・OH radicals is superior to that of g-C3N4, thus exhibiting higher catalytic activity. CH4 adsorption simulations and DRIFTS analyses show that CTF-1 has strong adsorption for methane, and dissociated water can promote the formation of methyl radicals. O2・- capture EPR indicates that the concentration of active O2 species on CTF-1 is low, inhibiting the excessive oxidation of methane and providing favorable conditions for C-C coupling to generate C2 products.
With the in-depth study of the "intramolecular junction," it is expected that by optimizing the catalyst composition, structure, and reaction conditions, the efficiency and selectivity of C-C coupling reactions can be further enhanced under very mild conditions, providing a foundation for low-carbon chemical engineering. On a broader application level, this technology breaks through the limitations of single utilization of methane, providing a new technical blueprint for the production of C2+ chemical family. From the perspective of the chemical industry, this technology will enrich the sources of raw materials, change the traditional pattern of petroleum-based chemical raw materials, and promote the transformation of the chemical industry towards a green and sustainable direction, utilizing abundant methane resources to build a new chemical synthesis industry chain. Particularly in the high-value conversion of distributed methane sources such as associated gas from oil fields, there is vast potential to expand the capture and utilization of methane waste gases in remote areas, reducing greenhouse gas emissions and converting them into valuable chemicals. This research achievement provides important references for developing efficient and stable C-C coupling photocatalysts and is expected to advance the application of photocatalytic technology in methane conversion and C2+ chemical synthesis, significantly contributing to the sustainable development of the energy and chemical industries.
Paper link: https://www.nature.com/articles/s41586-025-08630-x
Postdoctoral Recruitment Notice for Ammonia Synthesis in the Research Group of Academician Tang Junwang at Tsinghua University's Industrial Catalysis Center
Academic Leader: Tang Junwang
Tang Junwang (唐军旺) Professor, Academician of the Academia of Europaea, Senior Research Fellow of the Royal Academy of Engineering in the UK, Academician of the European Academy of Sciences in Belgium, Fellow of the Royal Society of Chemistry in the UK, Fellow of the International Association of Materials and Minerals, and Honorary Fellow of the Chinese Chemical Society. He has served as the Director of the Materials Center at University College London, Chair Professor of Material Chemistry and Material Engineering in the Department of Chemical Engineering, Changjiang Chair Professor of the Ministry of Education, and Vice President of the Association of Chinese Professors in the UK. Currently, he is the Director of the Industrial Catalysis Center in the Department of Chemical Engineering at Tsinghua University, the first Chair Professor of Carbon Neutrality at Tsinghua University, and also serves as a visiting professor at University College London and one of the 15 overseas directors of the Overseas-educated Scholars Association. Professor Tang has pioneered the coupling of photocatalysis and thermocatalysis to activate small molecules (H2O, N2, CH4, CO2) for the conversion and storage of renewable energy into hydrogen energy, green ammonia, and green alcohol, as well as microwave catalysis for recycling solid waste plastics. He is also committed to studying the mechanisms of light and heat coupling catalysis using time-resolved spectroscopy. He serves as an editor or associate editor for five international journals, including Applied Catalysis B, Chin J. Catal., and EES Solar. He has received multiple international awards and is currently recruiting several postdoctoral researchers.
The above research has received funding support from national foundation team projects and key projects from state-owned enterprises such as Sinopec, and excellent postdoctoral candidates are being recruited for these projects.
Recruitment Criteria:
(1) Postdoctoral candidates should generally be under 32 years of age; visiting scholars should be under 40 years old.
(2) A Ph.D. degree in the field of heterogeneous catalysis is required.
(3) Candidates should have rich experience in material preparation, characterization, and catalytic activity evaluation.
(4) Candidates should have published at least 3 high-level research papers as the first author in mainstream international journals in their field and be able to conduct independent research.
(5) Solid professional knowledge and rich practical experience are required.
(6) Strong English writing and international conference communication skills are essential.
(7) Good laboratory safety management skills are required.
Application Materials:
(1) Personal resume: including education, research direction and achievements (with three representative published papers attached), contact information of referees, and personal contact information;
(2) A one-page summary of the expected work direction and plan during the postdoctoral/visiting period.
Please consolidate the above application materials into a single PDF file and send it to Wang Laoshi at qywang@tsinghua.edu.cn with the email subject "Postdoctoral/Visiting Scholar Application - Name."
Outstanding candidates are recommended to apply for Tsinghua's Shuimu Scholars and funding for collaboration with international prestigious universities.
