ACTIVITY OF Ni-Fe CATALYSTS IN THE REACTION OF CO2 HYDROGENATION

Abstract

Under the same condition, a series of the catalysts of Ni-Fe system with different metal ratio (100–65 mass. % of Ni — 0–35 mass. % of Fe) were prepared by coprecipitation method with NH₄OH as a precipitation agent. All samples were reduced by He+H₂ mixture from oxide form to the metal state and then they were used in methane production from CO₂ and H₂. The optimal temperature (300°C) of Ni-Fe oxides reduction to metal condition was determined by TGA method. Based on the experimental data on loss of mass, activation energy (E_a) of samples' reduction for Ni₈₀Fe₂₀ and Ni₇₅Fe₂₅ was estimated. The explanation of such a significant difference in activation energy rates is the formation of intermetall FeNi₃ in the range of 72–77 mass % of Ni, as well as that the reduction activation energy of a particular substance is lower then in solid solution of γ+FeNi₃ within the concentration range of 60–70 mass. % and 80–100 mass. % of Ni.

Investigation of catalytic activity of Ni-Fe systems in the reaction of CO₂ hydrogenation was performed. Among the tested samples, Ni₈₀Fe₂₀ catalyst with the most specific surface area showed the best performance at 300–500°С, and the methane yield amounted to 62%. Ni₇₅Fe₂₅ sample with smallest specific surface area showed the worst catalytic performance in term of conversion of CO₂ and yield for CH₄. The correlation between samples' phase composition and their catalytic activity was estimated.