Hydrogenation of acetylene and propyne over hydrogen storage ErNi_5-xAl_x alloys and the role of absorbed hydrogen

The hydrogen storage properties of ErNi_5-xAl_x (x = 0, 0.5, 0.75, 1, 1.25, and 1.5) alloys were investigated by pressure-composition isotherms and in situ X-ray diffraction measurements under a hydrogen atmosphere. Catalytic reactivities toward the hydrogenation of alkynes (acetylene and propyne) over ErNi_5-xAl_x (x = 0, 1, and 1.5) alloys were also studied and the contribution of absorbed hydrogen to hydrogenation is discussed. All ErNi_5-xAl_x alloys possess a hexagonal structure (CaCu₅-type) with the space group P6/mmm. The substitution of Al for Ni facilitated hydrogen absorption at lower hydrogen pressures by the formation of larger interstitial spaces. ErNi_3.5Al_1.5H_n with absorbed hydrogen showed higher reactivities for the catalytic hydrogenation of acetylene and propyne than ErNi₅ and ErNi₄Al without absorbed hydrogen. The reason for this was concluded to be that absorbed hydrogen activates adsorbates (acetylene and hydrogen) that are supplied from the gas phase.