Studies on metal oxide nanoparticles catalyzed sodium aluminum hydride

This paper reports the catalytic activity of several metal oxide nanoparticles such as TiO2, CeO2, La2O3, Pr2O3, Nd2O3, Sm2O3, Eu2O3 and Gd2O3 for NaAlH4. TiO2 was found to be the most effective catalyst. In order to find the size dependence of TiO2 nanoparticles on the catalytic activity, TiO2 nanoparticles of different sizes such as 5 nm, 25 nm, 150 nm and 200 nm have been used. TiO2 nanoparticles lower the desorption temperature of sodium alanate (NaAlH4) from ∼ 473 K to ∼373 K. Using 5 nm and 25 nm TiO2 catalysts ∼3 wt% hydrogen could be released within 5-7 min at 423 K. TiO2 (25 nm) catalyst lowers the activation energy of NaAlH4 to 67 kJ/mol H2, as compared to 119 kJ/mol H2 for the pristine material. This is better than Ti nanoparticles catalyst of similar size which lowers the activation energy up to 77 kJ/mol H2. The long-term reversible characteristics of 25 nm TiO2 admixed NaAlH4 up to 35 cycles and the phase structural features of the cycled samples are discussed.