The effect of doping rare-earth chloride dopant on the dehydrogenation properties of NaAlH4 and its catalytic mechanism

A series of rare-earth chlorides has been adopted to catalyze dehydrogenation reaction of NaAlH4. X-ray diffraction analysis and isothermal dehydrogenation measurement have proved that these chlorides enhance the dehydrogenation kinetics and lower the decomposition temperature of NaAlH4. The catalytic effect from high to low is in following order: SmCl3>CeCl3>TiCl3>NdCl3>GdCl3>LaCl3>ErCl3SmCl3>CeCl3>TiCl3>NdCl3>GdCl3>LaCl3>ErCl3. In order to reveal the catalytic mechanism of the rare-earth chlorides on dehydrogenation reactions, systems doped with LaCl3 were investigated under different milling and dehydrogenation conditions. It has been proposed that the La cation reacts with hydrogen, which was released from NaAlH4, and then forms some sort of La–Al alloys. This process improves the performance of NaAlH4 dehydrogenation at a relatively low temperature. In the present research, the catalytic effect of La2O3 has also been investigated. Results show that La2O3 also have a catalytic effect on the dehydrogenation of NaAlH4, but the effect is less obvious than that of the rare-earth chlorides.