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>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.