Ability of hydrogen storage CeNi_5-xGa_x and Mg₂Ni alloys to hydrogenate acetylene

Abstract

Hydrogen storage properties and reactivity for hydrogenation of acetylene in a series of CeNi 5-x Ga x (x = 0, 0.5, 0.75, 1, 1.25, 1.5) alloys and Mg 2 Ni were determined and compared. The structure of CeNi 5 (CaCu 5 type) was maintained up to CeNi 3.5 Ga 1.5 when Ni was replaced by Ga. The replacement facilitated hydrogenation absorption by creating larger interstitial spaces through expansion of the lattice, allowing CeNi 4.25 Ga 0.75 to absorb the greatest proportion of hydrogen atoms among the alloys under the same conditions. The results showed that the absorbed hydrogen in CeNi 3.75 Ga 1.25 improved reactivity. In contrast, Mg 2 Ni formed a hydride upon hydrogenation of acetylene and thus possessed much lower activity. The difference of the activity of absorbed hydrogen between CeNi 5-x Ga x and Mg 2 Ni was confirmed from transient response tests under reaction gases alternately containing He and H 2 .

High Catalytic Activities of RENi5–xAlx (RE = La, Er) and Low Activity of Mg2Ni Following Hydrogen Uptake: The Role of Absorbed Hydrogen

“…Specifically, H-abs reacts only weakly with alkynes. Soga et al examined the hydrogenation of ethylene (C 2 H 4 ) over LaNi 5 H n and reported that the catalytic activity increased with increases in the amount of hydrogen storage, in agreement with our previous reports. − However, Soga’s work also showed that H-abs reacted with C 2 H 4 to form ethane (C 2 H 6 ) without the involvement of gas-phase hydrogen . Therefore, the role of H-abs in the catalytic reaction remains uncertain.…”

“…In fact, some hydrogen storage alloys have been applied as catalysts, such as in the hydrogenation of carbon dioxide. 8−10 Our group has also reported the hydrogenation of alkynes [acetylene (C 2 H 2 ) and propyne (C 3 H 4 )] over RENi 5 (RE = rare earth)-type hydrogen storage alloys (specifically, CeNi 5−x Al x , 11 CeNi 5−x Ga x , 12 and Er-Ni 5−x Al x 13 ) and has shown that hydrogen absorption by these materials further promotes alkyne hydrogenation. 11−13 This prior work demonstrated that H-abs activates the adsorbed alkyne and adsorbed hydrogen (H-ad) on the surface since the rate of hydrogen desorption from the bulk alloy is slower than the catalytic hydrogenation of alkynes on the hydride surface.…”

“…12,15 Mg 2 Ni is a wellknown hydrogen storage alloy that exhibits decreased reactivity toward the hydrogenation of C 2 H 2 after forming its hydride, Mg 2 NiH 4 . 12 Hodge and Goldberger reported that BaGa 2 H 2 shows lower reactivity during the hydrogenation of phenylacetylene compared with Zintl-phase BaGa 2 . 15 Hydrogen absorption has also been considered as a means of enhancing the hydrogenation of hydrocarbons in RENi 5 -type hydrogen storage alloys 11−14 or Pd catalysts.…”

High catalytic performance of Al–Pd–(Ru, Fe) icosahedral approximants for acetylene semi-hydrogenation

“…Intermetallic compounds (IMCs) exhibit a wide range of attractive functions and characteristics that are not attainable in ordinary elemental metals, such as a shape memory effect, 1 superconductivity. 2 and hydrogen absorption 3 They also possess excellent properties for hydrogenation catalysis, such as those demonstrated in Heusler alloys, 4,5 Zintl phases, 6 and hydrogen absorbing alloys. 3,7,8 Quasicrystals 9 are complex IMCs with aperiodic structures that often exhibit five-fold symmetry.…”

“… 2 and hydrogen absorption 3 They also possess excellent properties for hydrogenation catalysis, such as those demonstrated in Heusler alloys, 4,5 Zintl phases, 6 and hydrogen absorbing alloys. 3,7,8 Quasicrystals 9 are complex IMCs with aperiodic structures that often exhibit five-fold symmetry. Crystalline approximants, on the other hand, are periodic crystals having a similar chemical composition and atomic 10,11 and electronic structures 12 closely related to quasicrystals.…”