Deactivation and regeneration of Raney-Ni catalyst during multiphase dehydrogenation of cyclohexane

Hydrogen production via dehydrogenation of cyclohexane is regarded as one of the most promising on-board hydrogen supplier system for hydrogen vehicles. In this study, the deactivation mechanism of Raney-Ni catalyst under “wet-dry” multiphase reaction conditions was studied by means of characterizations. The fresh and deactivated Raney-Ni catalyst was characterized by scanning electron microscope (SEM), thermogravimetry analysis (TGA), X-ray spectroscopy (XRD), Brunauer-Emmett-Teller (BET), mercury porosimetry and granularity analysis. It was found that the deposition of the filamentous carbon, which came from the side reactions of cyclohexane, on the outer layers of Raney-Ni particles was the main reason for the catalyst deactivation. Due to the strong external diffusion resistance during the multiphase reaction process, the carbon was concentrated in the orifices, and the amount of carbon was about 3.25 wt.% of the catalyst. The decay of Raney-Ni was a typical orifice coking deactivation. The experimental study also showed that the deactivated Raney-Ni catalyst could be regenerated by coke elimination with water and recovered its activity. In addition, a regeneration mechanism of the deactivated catalyst by coke elimination was proposed.

Graphical abstractDeactivation and Regeneration of Raney-Ni Catalyst during Multiphase Dehydrogenation of CyclohexaneFigure optionsDownload full-size imageDownload as PowerPoint slide