Hematite nanoparticles in aquathermolysis: A desulfurization study of thiophene

• Hematite nanoparticles displayed good performance in decomposing thiophene.
• The catalytic performance increases with temperature and catalyst concentration.
• The use of hydrogen donor could reduce the catalytic activity.
• A cyclic phase transformation of hematite to magnetite was observed.

The potential usage of hematite nanoparticles as heterogeneous catalysts in aquathermolysis was investigated in this work. The desulfurization of thiophene was studied to investigate the catalytic activity of hematite in the aquathermolysis of heavy oil. It was found that reaction conditions, e.g., reaction time and temperature, ratio between thiophene and water, hematite nanoparticle size, catalyst concentration, and the presence of hydrogen donors, influenced the ability of hematite nanoparticles to decompose thiophene. Experimental results showed that thiophene conversion was increased with reaction time, temperature and catalyst concentration but decreased with thiophene/water ratio and particle size. Further analysis showed that the activity of the hematite nanocatalyst was also reduced in the presence of hydrogen donors. This is because hydrogen donors occupy the catalyst surface and block the catalytic sites. Furthermore, FTIR and XRD analyses revealed that thiophene underwent oxidative desulfurization to produce maleic acid, SO2 and CO2, whereas some areas of the hematite surface were transformed into magnetite. However, this magnetite was re-oxidized back into hematite in the presence of water as the source of active oxygen.