Unraveling Thermal Stability of Carbon Active Sites Chemisorbing Hydrogen on Oxygen-Containing Activated Carbons

• Published in: Journal of physical chemistry. C 2024-06, Vol.128 (24), p.9981-9992
• Main Authors: Baba, Takanori, Gabe, Atsushi, Hirahara, Takuma, Mikami, Takahiro, Oda, Naohiro, Kawata, Kazunori, Otake, Yoshinobu
• Format: Article
• Language: English
• Subjects: C: Chemical and Catalytic Reactivity at Interfaces
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.4c02056

Understanding surface chemistry on carbon edge sites is crucial to improving the performance of carbon materials, and carbon active sites are key topics in the reactivity of relevant reactions. In this study, the thermal stability of carbon active sites chemisorbing hydrogen present on carbon edge sites is studied by use of temperature-programmed desorption (TPD) and temperature-programmed reaction (TPR) techniques. The activated carbons oxidized in HNO3 (HNO3 CAL) are heat-treated under an argon atmosphere at various temperatures for 1 h in order to progressively remove the oxygen-containing functional groups followed by forming carbon active sites on the carbon edge sites. Afterward, TPR is performed in a flowing low-concentrated H2 on the HNO3 CAL and heat-treated HNO3 CALs up to 1273 K. The results indicate that atmospheric hydrogen is consumed for the evolution of H2O and CH4 and is chemisorbed on the carbon active sites which are newly generated as a result of the thermal decomposition of CO-yielding functional groups during the TPR. Then, by correlating the preheat treatment temperature in argon and the amount of hydrogen chemisorbed on the carbon surfaces, it is elucidated that the carbon active sites which chemisorbs hydrogen are deactivated in argon atmosphere especially when the preheat treatment temperature is higher than 950 K. Finally, this study shows the clear relationship between the preheat treatment temperature in argon and the amount of created carbon active sites chemisorbing hydrogen which are unraveling the thermal stability of carbon active sites on carbon edge sites.