Catalytic hydrogen generation from NaBH 4 /H 2 O system: effects of catalyst and promoters

Abstract

Abstract A hydrogen generation system based on NaBH4 hydrolysis is affected by the nature of the catalyst and catalyst promoter. Various catalyst promoters such as Al2O3 nanoparticles, Al2O3 particles, ZrO2 sand, SiO2, MMT clay, CNT and zeolite are compared with respect to hydrogen generation (HG) and hydrogen generation rate (HGR). The highest HG and HGR are observed with alumina nanoparticles as compared to other promoters. Cobalt chloride is found to be most efficient catalyst among the other cobalt based salts (CoCl2.6H2O, CoSO4.7H2O, (CH3COO)2Co.4H2O, Co(NO3)2.H2O), cadmium based salt (CdSO4) and copper based salt (CuSO4.5H2O). Maximum HGR obtained is 19.47 moles/L.sec for NaBH4 (1.26 moles/L)/Al2O3 nanoparticles (0.12 moles/L)/H2O and CoCl2.6H2O (0.02 moles/L) as catalyst at room temperature and atmospheric pressure. NaBH4 and alumina hydrolysis reactions, hydrophilic and amphoteric nature of alumina, affinity of Co+2 towards BH4 - ions and formation of aluminates are the factors that promote HGR, as illustrated in this work. Residue obtained from hydrolysis reaction is characterized for its elemental composition by the EDS technique, which confirmed a maximum percentage of boron in the residue. XRD and FTIR results concluded that adsorption of Na+ and Co+ ions occurred on the alumina surface and resulted in the formation of sodium aluminates and cobalt aluminates in the solution.