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Keywords:

  • dehydrogenation;
  • formic acid;
  • homogeneous catalysis;
  • ionic liquid;
  • ruthenium

Abstract

The dehydrogenation of formic acid is effectively catalyzed by the Ru complex [{RuCl2(p-cymene)}2] dissolved in the ionic liquid (IL) 1-(2-(diethylamino)ethyl)-3-methylimidazolium chloride at 80 °C without additional bases. This catalytic system gives TOF values of up to 1540 h−1. Preliminary kinetic insights show formal reaction orders of 0.70(±0.15), 0.78(±0.03) and 2.00(±0.17) for the Ru catalyst, IL 1, and formic acid, respectively. The apparent activation energy of this process is estimated to be (69.1±7.6) kJ mol−1. In addition, dimeric Ru hydride ionic species involved in the reaction, such as [{Ru(p-cymene)}2{(H)μ-(H)-μ-(HCO2)}]+ and [{Ru(p-cymene)}2{(H)μ-(Cl)μ-(HCO2)}]+, are identified by mass spectrometry. The presence of water in large amounts inhibits higher conversions. Finally, a remarkable catalytic activity is observed during recycles, indicating this system’s potential for hydrogen gas production.