Effects of oxygen functionalities on hydrous hydrazine decomposition over carbonaceous materials

Abstract

Metal-free heterogeneous catalysis is promising in the context of H₂ generation. Therefore, establishing structure–activity relationships is a crucial issue to improve the development of more efficient catalysts. Herein, to evaluate the reactivity of the oxygen functionalities in carbonaceous materials, commercial functionalized pyrolytically stripped carbon nanofibers (CNFs) were used as catalysts in the liquid-phase hydrous hydrazine decomposition process and its activity was compared to that of a pristine CNF material. Different oxygenated groups were inserted by treating CNFs with hydrogen peroxide for 1 h (O1-H₂O₂) and HNO₃ for 1 h (O1-HNO₃) and 6 h (O6-HNO₃). An increase in activity was observed as a function of the oxidizing agent strength (HNO₃ > H₂O₂) and the functionalization time (6 h > 1 h). A thorough characterization of the catalysts demonstrated that the activity could be directly correlated with the oxygen content (O6-HNO₃ > O1-HNO₃ > O1-H₂O₂ > CNFs) and pointed out the active sites for the reaction at carbon–oxygen double bond groups (CO and COOH). Systematic DFT calculations supported rationalization of the experimental kinetic trends with respect to each oxygen group (CO, C–O–C, C–OH and COOH).