Reactivity of 2-hydroxyethylhydrazinium nitrate (HEHN) with atomic iridium on graphite

Abstract

In order to develop chemical kinetics models for the ignition and combustion of ionic liquid-based fuels, identification of the elementary steps in the thermal and catalytic decomposition of components such as 2-hydroxyethylhydrazinium nitrate (HEHN) is needed but is currently not well understood. The first decomposition step in protic ionic liquids such as HEHN is typically the proton transfer from the cation to the anion, resulting in the formation of 2-hydroxyethylhydrazine (HEH) and HNO₃. In this investigation, temperature-programmed desorption mass spectrometry (TPD-MS) and x-ray photoelectron spectroscopy (XPS) are used to investigate the heterogeneous catalytic decomposition of HEHN with iridium. HEHN is introduced onto a highly-oriented pyrolytic graphite (HOPG) substrate (approx. 100 monolayers (ML)) and mass-selected iridium atoms (0–10 % ML) are deposited on the HOPG surface. The products can be identified by their masses, and product distributions are monitored as a function of surface temperature and Ir coverage. Formation of product species on the bare HOPG versus on the HOPG with increasing Ir coverage (5, 10 % Ir) indicates that the presence of iridium enhances various reactions. XPS confirms the presence of iridium on the surface and indicates the possible chemical bonding states involved. The products and their possible elementary reaction mechanisms are discussed.