Résumé
Methanolysis of sodium borohydride (NaBH(4)) is a way of recovering the hydrogen stored in the hydride. Though the reaction is spontaneous, it can be accelerated by virtue of Co-TiO(2) or Ru-TiO(2) catalysts. Under our experimental conditions, Co-TiO(2) shows high catalytic performances, higher than those of Ru-TiO(2). Hydrogen generation rates of 144 to 644 L(H(2)) min(-1) g(-1)(Co) were measured as the Co content was decreased. The kinetic parameters of the catalyzed reaction were determined. The Co-TiO(2)- catalyzed methanolysis follows a power law, i.e. r(20) k center dot[NaBH(4)](1.3)center dot[CH(3)OH](0.9) with k = 1.8 x 10(-2) s(-1). The Langmuir-Hinshelwood bimolecular mechanism accounts for the kinetics. The apparent activation energy was found to be 20.4 kJ mol(-1) whereas that of the catalyzed hydrolysis was 49.4 kJ mol(-1). Indeed, the catalyzed methanolysis was compared to the catalyzed hydrolysis as well as the catalyzed ethanolysis. For instance, it was remarked that water in methanol has a detrimental effect on the H(2) release kinetics. In parallel, the gravimetric hydrogen density of the system NaBH(4)-CH(3)OH has been optimized. Under our experimental conditions, it was found that the highest capacity that can be achieved is 3.4 wt%.