Formation of Ni-rich Ni-Ga alloy clusters on the (221) surface of Ni₅Ga₃ intermetallic compounds during CO₂ hydrogenation: An in-situ TEM study

Ni-Ga alloys are the most promising bimetallic alloy catalysts for CO₂ hydrogenation due to their high activity and selectivity. This study used in-situ transmission electron microscopy (TEM) to clarify the structural changes in the Ni₅Ga₃ intermetallic compound catalysts during the CO₂ oxidation and CO₂ hydrogenation processes. The results showed that as the temperature increased from 50 °C to 300 °C under CO₂ conditions, crystalline Ga oxides, primarily the β-Ga₂O₃ phase, formed on the Ni₅Ga₃(211) surface, resulting in the formation of parallel moiré fringes. At the same time, Ni-rich Ni-Ga alloy nanoclusters appeared due to the excess Ni on the surface. Under H₂/CO₂ conditions, Ni-rich Ni-Ga alloy nanoclusters were also observed, but the formation of Ga oxide was limited. Electron energy loss spectroscopy (EELS) analysis also revealed the presence of Ga oxide but not Ni oxide phase.