Design and Controlled Synthesis of Cobalt-Loaded Multi-Walled Carbon Nanotube-Magnetite Nanocomposite as Catalysts for Hydrogen Generation Via Hydrolysis of NABH4 Under Microwave Heating

Microwave (MW) irradiation is an attractive option for process intensification and has been proved effective in many catalytic processes. In this work, the (CNTs-Fe3O4)-Co nanocomposites were carefully design and successfully fabricated under a controlled manner. It was found that for the (CNTs-Fe3O4)(1:4)-Co (10 wt%) catalyst, in the temperature range of 40 to 60℃, MW heating led to the hydrogen generation rate (HGR) being improved by 75 to 95.4% as compared with conventional heating. The synergistic effect of cobalt and Fe3O4 sites of the (CNTs-Fe3O4)(1:4)-Co (10 wt%) catalyst was also verified by the evaluation of the catalytic performance of the (CNTs-Fe3O4) catalysts with different Co loading and DFT calculations. Moreover, the pre-exponential factor (A) of the NaBH4 hydrolysis catalyzed by the (CNTs-Fe3O4)(1:4)-Co (10 wt%) catalyst under MW heating was approximately 15 times higher than that of conventional heating, indicating that the effective collision frequency of the atoms at the reaction interface of the catalyst under MW heating was much higher than that of conventional heating because of the higher active sites on the surface of (CNTs-Fe3O4)(1:4)-Co (10 wt%) catalyst under MW irradiation. Furthermore, the designed continuous experiment with microwave intermittent off-on (5 min as a reaction cycle) was carried out at 26±0.3℃ controlled by a continuous thermostatic water bath, and the results proved that both thermal and non-thermal effects of MW heating contributed to the enhancement of HGR under MW heating.