Efficient Hydrogen Production by Combined Reforming of Methane over Perovskite-Derived Promoted Ni Catalysts

Efficient production of H₂ by combined (steam/CO₂; steam/O₂) reforming of CH₄ was comparatively studied over perovskite-derived promoted Ni catalysts. The process performance was improved by regulating the redox and structural properties of the LaNi_0.99M_0.01O₃ catalysts through promotion (M = Pt, Pd, Re, Mo, Sn). The catalysts were synthesized using the citrate sol–gel method, tested in combined reforming of methane and studied by X-ray fluorescence analysis, thermal analysis, N₂ adsorption, X-ray diffraction, electron microscopy, temperature-programed hydrogen reduction to elucidate the impact of catalyst properties on their activity and resistance to re-oxidation and formation of carbon deposits under reaction conditions. It was shown that LaNi_0.99M_0.01O₃ catalysts after calcination at 850 °C in air have a perovskite structure that was destroyed after reductive activation with formation of metal Ni^o particles with an average size of ~ 25 nm on the surface of lanthanum oxide/hydroxide. The resistance to re-oxidation of Ni^o particles depends on the type of promoter and is maximum in the case of M = Re. It was established that the type of promoter affects the conversion of reagents (CH₄, CO₂) and the H₂ yield, which at 700 °C increases in the series of promoters Sn < Mo < Pt < Pd < Re in the case of steam/CO₂ reforming and Pt < Sn < Mo < Pd < Re with steam/O₂ reforming. The optimal composition of catalyst was identified: among the studied samples, LaNi_0.99Re_0.01O₃ is characterized by a higher specific surface area, average reduction ability and high resistance to re-oxidation and coking. At 850 °C it provides the H₂ yield of 95 and 50% at complete CH₄ conversion in steam/CO₂ and steam/O₂ reforming, respectively.