The effect of doping rare-earth chloride dopant on the dehydrogenation properties of NaAlH_4 and its catalytic mechanism

摘要

A series of rare-earth chlorides has been adopted to catalyze dehydrogenation reaction of NaAlH_4. X-ray diffraction analysis and isothermal dehydrogenation measurement have proved that these chlorides enhance the dehydrogenation kinetics and lower the decomposition temperature of NaAlH_4. The catalytic effect from high to low is in following order: SmCl_3>CeCl_3>TiCl_3>NdCl_3>GdCl_3>LaCl_3>ErCl_3. In order to reveal the catalytic mechanism of the rare-earth chlorides on dehydrogenation reactions, systems doped with LaCl_3 were investigated under different milling and dehydrogenation conditions. It has been proposed that the La cation reacts with hydrogen, which was released from NaAlH_4, and then forms some sort of La-Al alloys. This process improves the performance of NaAlH_4 dehydrogenation at a relatively low temperature. In the present research, the catalytic effect of La_2O_3 has also been investigated. Results show that La_2O_3 also have a catalytic effect on the dehydrogenation of NaAlH_4, but the effect is less obvious than that of the rare-earth chlorides.