> ## Content Index > Fetch the complete content index at: https://research-pop.com/llms.txt > Use this file to discover other available public pages before exploring further. # National University of Singapore-led team uses plasma to build nitrogen-rich carbon with dispersed platinum for ambient-pressure ammonia production - URL: https://research-pop.com/national-university-of-singapore-led-team-uses-plasma-to-build-nitrogen-rich-carbon-with-dispersed-platinum-for-ambient-pressure-ammonia-production/ - Published: 2026-09-11T13:27:39.000Z - Updated: 2026-09-11T13:28:08.000Z - Author: ResearchPOP - Tags: Energy ![](https://storage.ghost.io/c/7c/5e/7c5e0911-739b-4a35-94eb-3e810bf78ba7/content/images/2026/09/Screenshot-2026-09-11-at-14.48.01-1.png) Source: [https://www.nature.com/articles/s41467-026-77160-5](https://www.nature.com/articles/s41467-026-77160-5?ref=research-pop.com) ## **At a glance** Researchers from the National University of Singapore, Xi’an Jiaotong University, Shinshu University, the Institute of Wenzhou at Zhejiang University, CSIRO, the University of Nottingham Ningbo China, the University of Manchester, Princeton University, Tohoku University and the University of California, Davis have connected plasma-emission measurements, catalyst formation and ambient-pressure ammonia production in one study. The team aimed to combine three useful material properties: a high nitrogen content, an ordered graphitic structure and platinum dispersed as both isolated species and small clusters. Using pulsed plasma at a liquid–liquid interface, they produced a urea/cyclohexane-derived material containing 22.4 at.% nitrogen and approximately 7.5 wt.% platinum. Microscopy showed Pt clusters with average diameters of 1.5–1.8 nm alongside bright features assigned to isolated Pt atoms. In an ambient-pressure dielectric-barrier-discharge reactor, the material produced an NH₃ concentration of 2.13% with 1.13% N₂ conversion at 9 kV, 8 kHz, an N₂/H₂ ratio of 1:1 and a total flow rate of 20 mL (NTP) min⁻¹. Spectroscopy, isotope experiments and calculations support the authors’ proposed cooperative pathway: isolated Pt helps activate N₂, Pt clusters promote H₂ dissociation and nitrogen sites in the carbon material may also participate in NH₃ formation. Beyond the catalyst performance, the study explores whether the light emitted by plasma can provide useful clues for selecting molecular precursors and designing nitrogen-rich carbon materials. ## Background Nitrogen-doped graphitic carbon is widely studied as a catalyst support. Nitrogen sites can help anchor metal atoms and prevent them from moving and forming larger particles, while an ordered graphitic structure can support charge transfer and material stability. Producing these features together can be challenging. Conventional graphitization usually requires high temperatures, which can remove nitrogen from the carbon structure and encourage metal species to migrate and aggregate. Researchers therefore seek alternative routes that can retain nitrogen while producing an ordered carbon framework and highly dispersed metal sites. Nonthermal plasma provides a different chemical environment. Energetic electrons generate radicals, ions and excited molecules that can drive precursor decomposition, polymerization, carbonization and metal-ion reduction. This allows several steps in material formation to occur together within a highly reactive, non-equilibrium environment. The team also wanted to understand whether the chemical species produced in the plasma could be followed through optical emission. If particular light-emission signals are associated with specific material properties, they could help researchers choose suitable molecular precursors for future syntheses. The resulting Pt-containing carbon material was then tested in nonthermal plasma-assisted ammonia production. In this study, “ambient pressure” means that the reaction was conducted near atmospheric pressure, rather than under the high-pressure conditions commonly used in the Haber–Bosch process. ## Research question The study explored two connected questions. First, could CN, C₂, CH, H and atomic-C signals in plasma optical emission help predict which precursors would form nitrogen-rich, graphitically ordered carbon while platinum was reduced and stabilized? Second, could isolated Pt atoms, Pt clusters and nitrogen-doped carbon perform complementary roles during ambient-pressure plasma-assisted ammonia production? ## Inside the study Catalyst preparation took place in a 200 mL biphasic reactor. The lower aqueous phase contained approximately 100 mL of 0.1 mmol L⁻¹ H₂PtCl₆ solution. The upper organic phase contained approximately 100 mL of a urea/cyclohexane, pyridine/cyclohexane or aminopyridine/cyclohexane mixture. A copper-disc electrode was placed in the organic phase approximately 0.5 cm above the liquid–liquid interface, while a stainless-steel electrode contacted the grounded aqueous phase. Bipolar pulses with a peak voltage of 2 kV, a frequency of 30 kHz and a pulse width of 1 μs were applied for 45 min. During operation, transient microbubbles formed near the liquid–liquid interface, and plasma discharges developed inside them. The energetic electrons and reactive species promoted the formation of nitrogen-doped carbon while simultaneously reducing the platinum precursor and stabilizing the resulting Pt species within the carbon framework. ![](https://storage.ghost.io/c/7c/5e/7c5e0911-739b-4a35-94eb-3e810bf78ba7/content/images/2026/09/Screenshot-2026-09-11-at-15.03.40.png) **Fig. 1\. Double layer solution plasma synthesis and discharge characteristics.** Changing the precursor produced clear differences in material composition. The urea/cyclohexane-derived product contained 22.4 at.% nitrogen and approximately 7.5 wt.% Pt. The pyridine system produced a material containing 16.3 at.% nitrogen and approximately 5.2 wt.% Pt, while the aminopyridine system produced a material containing 9.4 at.% nitrogen and approximately 3.9 wt.% Pt. For the urea-derived material, analysis of the N 1s XPS spectrum assigned 52.5% of the fitted nitrogen signal to graphitic nitrogen, 32.8% to pyridinic nitrogen and 14.7% to pyrrolic nitrogen. These nitrogen environments can influence the electronic properties of the carbon framework and provide different coordination sites for platinum. ![](https://storage.ghost.io/c/7c/5e/7c5e0911-739b-4a35-94eb-3e810bf78ba7/content/images/2026/09/Screenshot-2026-09-11-at-15.04.09.png) **Fig. 2\. Structural characterization and platinum coordination environments of N doped graphitic carbon catalysts.** HAADF-STEM and HRTEM revealed Pt clusters with average diameters of approximately 1.5–1.8 nm. The images also contained individual bright features assigned to isolated Pt atoms, showing that platinum was present in both isolated and clustered forms. EXAFS provided additional information about the average coordination environment around Pt. A dominant light-atom coordination shell appeared near 1.6 Å before phase correction, together with a weaker Pt–Pt contribution near 2.7 Å. The fitted Pt–Pt coordination number was approximately 1.2, far below the value of 12 for bulk platinum. Together with XPS, microscopy and DFT calculations, these results support a structure containing highly dispersed Pt species associated with Pt–Nₓ-like environments and small Pt clusters. ![](https://storage.ghost.io/c/7c/5e/7c5e0911-739b-4a35-94eb-3e810bf78ba7/content/images/2026/09/Screenshot-2026-09-11-at-15.04.48.png) **Fig. 3\. Multi-dimensional correlation between plasma-emission characteristics and carbon structure.** To identify optical signals that could guide precursor selection, the team studied 53 neat cyclic organic compounds in a separate pin-to-pin plasma reactor. The molecules covered different ring sizes, degrees of unsaturation, nitrogen contents and functional groups. Optical emission between 200 and 1000 nm was summarized using 24 descriptors associated with H, C₂, CN, CH and atomic-C emission. The researchers then related these descriptors to the crystallinity, defect structure and nitrogen content of the resulting carbon materials. The analysis showed that C₂-rich plasma emission was generally associated with a more ordered graphitic structure. Strong CN emission was linked to greater nitrogen incorporation, while H-rich emission was associated with carbon containing more defects and smaller sp² domains. Machine-learning analysis offered another way to examine these relationships. Using 80% of the data for training and 20% for testing, the best-performing multilayer-perceptron model reached R² = 0.67\. Similar train–test divisions produced broadly consistent rankings of the most important descriptors. SHAP analysis identified CN and C₂ emission as positive descriptors for nitrogen incorporation, while Hβ showed a negative association. The results suggest that plasma optical emission could provide a practical way to connect precursor chemistry with the properties of the carbon materials that form. The team then tested the urea/cyclohexane-derived Pt/nitrogen-doped graphitic carbon catalyst for plasma-assisted ammonia production. A total of 100 mg of catalyst was mixed with 200 mg of inert quartz sand, formed into 30–40 mesh granules and placed inside a coaxial dielectric-barrier-discharge reactor. The feed contained N₂ and H₂ in a 1:1 ratio at a total flow rate of 20 mL (NTP) min⁻¹. The discharge frequency was fixed at 8 kHz, and the applied voltage was varied from 6 to 9 kV. Both the NH₃ concentration and N₂ conversion increased as the voltage rose. At 9 kV, the plasma-derived catalyst produced an NH₃ concentration of 2.13% and an N₂ conversion of 1.13%. Under the same plasma and flow conditions, plasma without a catalyst and commercial nitrogen-doped graphene each produced approximately 0.2% NH₃. Commercial Pt/XC72 containing approximately 10 wt.% Pt produced 0.48% NH₃ at 9 kV. These comparisons highlight the benefit of combining nitrogen-doped graphitic carbon, isolated Pt species and small Pt clusters within the same catalyst. The reported electrical energy yield was 3.97 g NH₃ kWh⁻¹ at a discharge power of 4.55 W and a specific energy input of 13.65 kJ L⁻¹. These values describe the electrical performance of the laboratory plasma reactor under the reported operating conditions. ![](https://storage.ghost.io/c/7c/5e/7c5e0911-739b-4a35-94eb-3e810bf78ba7/content/images/2026/09/Screenshot-2026-09-11-at-15.05.59.png) **Fig. 4\. Plasma-catalytic ammonia synthesis performance of Pt supported on N-doped graphitic carbon catalyst in a flow reactor.** To understand how the different sites might work together, the researchers combined in situ infrared spectroscopy, nitrogen-isotope experiments and DFT calculations. When the plasma was switched on, in situ DRIFTS detected bands assigned to adsorbed N₂ and NHₓ/NH₃ species. These signals are consistent with N₂ activation and the stepwise hydrogenation of nitrogen-containing intermediates on the catalyst surface. In an isotope-switching experiment, the researchers first introduced ¹⁵N₂ and then changed the feed to ¹⁴N₂. A temporary ¹⁵NH₃ signal was observed after the switch, supporting the presence of nitrogen-containing species that remained on the catalyst and continued to react. Experiments using Ar/H₂ also suggested that some nitrogen associated with the catalyst could enter the NH₃ product. DFT calculations helped clarify the possible roles of the different Pt structures. In the models used by the authors, isolated Pt sites were more favourable for N₂ activation, while Pt clusters promoted H₂ dissociation and supplied hydrogen species for subsequent reaction steps. The calculated limiting free-energy barrier was 1.92 eV on isolated Pt and 1.14 eV on a Pt cluster. When isolated Pt and a Pt cluster were combined in a coupled-site model, the barrier decreased to 1.05 eV. Based on these results, the authors proposed a cooperative mechanism. Isolated Pt sites help activate N₂, while Pt clusters dissociate H₂ and provide reactive hydrogen for the gradual formation of NH₃. Nitrogen associated with Pt–Nₓ–C sites may also participate through a Mars–van Krevelen-like pathway and subsequently be replenished by activated nitrogen species. The catalyst was operated continuously for 85 h at 8 kV. During this period, the NH₃ concentration remained near 1.6% and the N₂ conversion remained near 0.8%, demonstrating stable ammonia production throughout the test. After the reaction, the Pt clusters remained within the 1.5–1.8 nm size range, with no clear evidence of substantial Pt sintering. XPS continued to show the presence of both Pt⁰ and Pt^δ+ species. The total nitrogen content changed from 22.4 at.% before the reaction to approximately 17 at.% afterwards, consistent with changes in the nitrogen environments during prolonged plasma operation. ## Takeaways and outlook The study demonstrates how plasma can play two roles within one research strategy. A biphasic liquid–liquid plasma first creates nitrogen-rich graphitic carbon containing both isolated Pt species and small Pt clusters. The resulting material then supports ammonia production in an ambient-pressure nonthermal plasma reactor. By studying 53 cyclic organic precursors, the researchers also connected CN, C₂ and Hβ emission with nitrogen incorporation and graphitic ordering. This creates a possible route for using plasma light as a measurable guide when selecting precursors and designing carbon materials. The combination of isolated Pt, Pt clusters and nitrogen-containing carbon sites is another central part of the study. Spectroscopy, isotope experiments and DFT calculations together support a cooperative reaction picture in which different sites contribute to N₂ activation, H₂ dissociation and the gradual formation of NH₃. Future work can expand the precursor library, optimize the catalyst and plasma reactor, and explore the approach over longer operating periods and at larger scales. The relationships between plasma emission, material structure and catalytic performance could also support the development of other plasma-assisted materials and reactions. ## About the researchers Jiangqi Niu (National University of Singapore) is the first author of the study. Shan Ding (National University of Singapore), Xu Ma (National University of Singapore; Xi’an Jiaotong University), Zheng Lian (National University of Singapore), Chayanaphat Chokradjaroen (Shinshu University), Shijie Xian (Institute of Wenzhou, Zhejiang University), Sana Ullah (CSIRO Energy), Xiaohan Chen (National University of Singapore), Yunxia Yang (CSIRO Energy), Rusen Zhou (Xi’an Jiaotong University), Renwu Zhou (Xi’an Jiaotong University) and Anthony B. Murphy (CSIRO Technology) also contributed to the research. Xiaolei Fan (Institute of Wenzhou, Zhejiang University; University of Nottingham Ningbo China; University of Manchester), Yiguang Ju (Princeton University; Tohoku University), Bruce C. Gates (University of California, Davis) and Sibudjing Kawi (National University of Singapore) are the corresponding authors. ## Original research Jiangqi Niu; Shan Ding; Xu Ma; Zheng Lian; Chayanaphat Chokradjaroen; Shijie Xian; Sana Ullah; Xiaohan Chen; Yunxia Yang; Rusen Zhou; Renwu Zhou; Anthony B. Murphy; Xiaolei Fan; Yiguang Ju; Bruce C. Gates; Sibudjing Kawi. “Plasma radicals control synthesis of platinum supported on nitrogen-doped graphitic carbon for ambient-pressure ammonia synthesis.” Nature Communications (2026). DOI: 10.1038/s41467-026-77160-5\. Published online 10 September 2026\. Image credit: Niu et al., Nature Communications (2026). Open access under CC BY-NC-ND 4.0\. Images reproduced without modification. --- ## Research POP Notes This article reflects the independent interpretation of the Research POP team and does not represent the views of the authors, their institutions or the journal. 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