Ni3GaC0.25 Catalyst for Dry Reforming of Methane

Seok Ki Kim, Korea Research Institute of Chemical Technology (KRICT), Daejeon, Kwangjin An, Jae Sung Lee, and colleagues, Ulsan National Institute of Science and Technology (UNIST), Republic of Korea, have synthesized a NiMgGa layered double hydroxide (NMG-LDH) as a catalyst precursor for the dry reforming of methane.

The team dissolved nickel(II) nitrate hexahydrate [Ni(NO₃)₂-6H₂O], magnesium(II) nitrate hexahydrate [Mg(NO₃)₂-6H₂O], and gallium(III) nitrate hydrate [Ga(NO₃)₃-xH₂O] in water. They added a solution containing sodium carbonate (Na₂CO₃) and sodium hydroxide (NaOH) in water. After stirring, the solution was sealed in an autoclave and kept at 120 °C for 24 hours. After cooling, a green precipitate was collected by filtration and dried in a vacuum oven. Samples of this NMG-LDH were reduced in 50 % H₂/Ar at various temperatures. The obtained catalysts consisted of crystalline Ni₃Ga nanoparticles (NPs) embedded in MgO nanosheets. Ni and Ga are uniformly distributed in the Ni₃Ga NPs on the MgO support.

The researchers performed the dry reforming of methane in a fixed-bed quartz reactor. During the reaction, the reversible phase transition between Ni₃Ga and Ni₃GaC_x activates both CO₂ and CH₄ (pictured). Interstitial carbon is an important reaction intermediate: Carbon atoms dissociated from CH₄ enter the interstices of the Ni₃Ga lattice during dry reforming of methane at 600 °C. By this, the Ni₃Ga catalyst is converted into a Ni₃GaC_0.25 phase. This intermetallic carbide readily reacts with CO₂ to form CO. This prevents the formation of coke on the catalyst surface and avoids deactivation of the catalyst by coking. The mechanism is unique in that the interstitial carbon becomes the reactive intermediate, whereas in most heterogeneous catalysts only surface intermediate species are involved.

The Ni₃Ga/MgO catalyst shows ∼48 % CH₄ and ∼52 % CO₂ conversion and excellent stability against coking during dry reforming of methane. According to the researchers, their results provide valuable insights for preparing intermetallic catalysts with a high stability against coking.