| The key to the efficient hydrolysis of sodium borohydride for hydrogen production depends on catalysts.Precious metal catalysts are not suitable for large-scale industrial applications because of their high price.The non-noble metal Co-B has been extensively investigated due to its high activity and low preparation cost.However,the exothermic reduction reaction of cobalt leads to the defects of Co-B alloy such as elevated surface energy,poor thermal stability,inhomogeneous particles and easy aggregation,which limit its application in efficient hydrogen production by hydrolysis.Mo-doped Co-B catalyst can enhance the surface activity of Co-B and reduce the activation of the reaction,but it still has the disadvantages of easy agglomeration and lack of stability.In this paper,Co-Mo-B/r-GO,Co-Mo-B/ZIF-67 and Co-Mo-B/ZIF-67@GO catalysts were prepared by chemical reduction method to improve the activity and stability of Co-Mo-B catalysts.The hydrolysis kinetics of the catalyst catalyzed by the hydrolysis of sodium borohydride for hydrogen production under the optimal loading amount was also studied.The main studies are as follows:（1）Co-Mo-B catalyst was prepared by chemical reduction method.In this chapter,the effects of different Mo/Co doping ratio and hydrolysis conditions on the catalytic performance of the catalyst were studied.At the same time,excessive Mo doping resulted in the increase of oxides in Co-Mo-B.When Mo/Co was 0.05,the Co-Mo-B-1 catalyst maintained the amorphous structure and it had specific surface area of 53.2 m2/g.Co-Mo-B-1 exhibited the best activity of 3095.4 mL · min-1·g-1.The optimal hydrolysis conditions of sodium borohydride catalyzed by Co-Mo-B-1 were 1.0 mol/L NaBH4 and 1.0 mol/L NaOH.After five cycles,the activity of the catalyst remained at 58.93%of the initial activity.（2）Graphene oxide supported Co-Mo-B catalyst was prepared by chemical reduction method.The results show that the dispersion and particle size of Co-Mo-B alloy can be effectively improved with the introduction of graphene oxide.The amorphous structure of CoMo-B in the catalyst had not been changed.At the same time,graphene oxide（GO）was reduced to reduced graphene oxide（r-GO）during the preparation.r-GO can contribute to the movement of electrons between metal active sites and reactions.When the addition of GO was 0.015 g,the specific surface area of Co-Mo-B/r-GO-3 catalyst increased obviously to 87.6 m2/g.At this time,the catalyst showed the highest activity of 4689.5 mL·min-1· g-1,which was 1.5 times that of unsupported Co-Mo-B.The optimal hydrolysis conditions of sodium borohydride catalyzed by Co-Mo-B/r-GO-3 were 1.0 mol/L NaBH4 and 2.0 mol/L NaOH.Compared with Co-Mo-B,the catalyst not only had lower activation energy（35.06 kJ/mol）but also higher stability.The catalyst retained 70.25%of the initial activity after five cycles.（3）ZIF-67 supported Co-Mo-B catalyst was synthesized by chemical reduction method.After the introduction of ZIF-67,the dispersion of Co-Mo-B alloy was significantly improved.Meanwhile,the addition of ZIF-67,the did not change the amorphous structure of Co-Mo-B alloy.The rhombohedral dodecahedral structure of ZIF-67 can provide high density active sites for hydrolysis and significantly increase the specific surface area of the catalyst.When the addition of ZIF-67 was 0.100 g,the specific surface area of Co-Mo-B/ZIF-67-4 catalyst（165.3 m2/g）and the catalytic activity of 8072.8 mL · min-1·g-1were the highest among the three supported Co-Mo-B catalysts.The optimal hydrolysis conditions of sodium borohydride catalyzed by Co-Mo-B/r-GO-3 were 2.0 mol/L NaBH4 and 3.0 mol/L NaOH.Compared with Co-Mo-B/r-GO-3,the catalyst not only had lower activation energy（23.34kJ/mol）,but also had higher stability.It retained 82.36%of the initial activity after five cycles.（4）ZIF-67@GO supported Co-Mo-B catalyst was synthesized by chemical reduction method.ZIF-67@GO was synthesized by in situ growth of ZIF-67 crystals on both surfaces of graphene oxide（GO）.The introduction of ZIF-67@GO did not change the amorphous structure of Co-Mo-B alloy in the catalyst.ZIF-67@GO can improve the dispersion of CoMo-B and provide an anchoring platform for it.When the addition of ZIF-67@GO was 0.060 g,the specific surface area of Co-Mo-B/ZIF-67@GO-3 was 63.7 m2/g.The catalyst exhibited highest catalytic activity of 6598.6 mL · min-1 · g-2,which was 2.2 times that of unsupported Co-Mo-B.The optimal hydrolysis conditions of sodium borohydride catalyzed by Co-MoB/ZIF-67@GO-3 were 1.5 mol/L NaBH4 and 2.0 mol/L NaOH.Compared with Co-MoB/ZIF-67-4,the activation energy of the catalyst had a higher activation energy of 27.92 kJ/mol.Its stability was lower than that of Co-Mo-B/r-GO-3 and Co-Mo-B/ZIF-67-4 catalysts.After five cycles,the activity of the catalyst reained at 68.92%of the initial activity. |
