Long-term thermal stability of selected ionic liquids in nitrogen and hydrogen atmosphere

• The [NTf2] anion is the most stable anion among those investigated.
• Among the monocationic ILs, [N1114][NTf2] and [PMPip][NTf2] are long-term stable up to 300 °C.
• In particular, dicationic ILs show a good thermal stability at 300 °C during isothermal experiments.
• A hydrogen containing atmosphere drastically reduces the thermal stability of ILs.
• The presence of a nickel/Al2O3 catalyst reduces thermal stability.

Approximately 30 ionic liquids with different cations and anions were manufactured and tested for their thermal stability. In addition to common cations (e.g., imidazolium and ammonium), novel cations such as several dications, a bicyclic amine, a benzimimidazolium, and an inorganic cation were applied.All liquids were heated to the desired temperature by applying a constant heating rate of 3 K/min. After the heating period, the temperature was held for at least 6 h in a nitrogen-atmosphere. Some ionic liquids based on the [NTf2]-anion tend to be stable up to 250 °C or even 300 °C in N2 atmosphere. In particular, imidazolium and pyrrolidinium dicationic ionic liquids show a high thermal stability. The salt [Li][NTf2], which provides an inorganic cation, decomposes at temperatures between 250 and 300 °C.Additionally and with respect to technical application, the effect of hydrogen and nickel on the thermal stability of ILs was studied. Both nickel and hydrogen reduce the thermal stability, whereas the effect of hydrogen on the thermal stability of ILs is drastic.