CO 2 hydrogenation into CH 4 over Ni–Fe catalysts Reza Meshkini Far, Olena V. Ischenko, Alla G. Dyachenko, Oleksandr Bieda, Snezhana V. Gaidai and Vladyslav V. Lisnyak * Chemical Faculty, Taras Shevchenko National University of Kyiv, Kyiv 01601, Ukraine * lisnyak@univ.kiev.ua Received 21 February 2018; Accepted 18 April 2018; Published Here, we report, for the first time, on the catalytic hydrogenation of CO 2 to methane at atmospheric pressure. For the preparation of hydrogenation catalysts based on Ni and Fe metals, a convenient method is developed. According to this method, low-temperature reduction of the co-precipitated Ni and Fe oxides with hydrogen gives the effective and selective bimetallic Ni 70 Fe 30 , Ni 80 Fe 20 and Ni 90 Fe 10 catalysts. At the temperature range of 300–400 ○ C, they exhibit a high efficiency of CH 4 production with respect to monometallic Ni and Fe catalysts. The results imply a synergistic effect between Ni and Fe which caused the superior activity of the Ni 80 Fe 20 catalyst conversing  67% of CO 2 into CH 4 at 350 ○ C. To adapt the Ni–Fe catalysts in the industry, the effect of two different carriers on the efficiency of the alumina-supported Ni 80 Fe 20 catalyst was investigated. It is found that the Ni 80 Fe 20 /α-Al 2 O 3 catalyst effectively conversed CO 2 giving 100% methane yield already at 275 ○ C. Keywords : Hydrogenation of CO 2 ; Ni–Fe catalysts; atmospheric pressure methanation; Ni–Fe/Al 2 O 3 . Carbon dioxide is a gaseous pollutant broadly presented in the atmosphere. From the economic and environmental reasons, catalytic hydrogenation of CO 2 to CH 4 has a great challenge among scaled-up methods of reducing air pollution. 1 Consequently, the development of a metal catalyst that has advanced activity and selectivity to CH 4 is important. For fairly high CH 4 yields, the CO 2 hydrogenation has been studied over numerous supported metal catalysts. 2–5 But the efficient Ni metal catalysts fulfill the recent requirements for the most. 5,6 In contrast to the Ni metal catalyst, the supported Fe metal is a weak catalyst that failed to generate a comparable amount of CH 4 . 7,8 However, the recent computational screening 9 has indicated that Ni–Fe catalysts could be more efficient than the pure Ni metal catalyst. Therefore, the Ni–Fe catalysts have a significant potential to be used in the safe environmental process. 10 However, as far as we know, there is no report about preparing advanced methanation catalyst except Ni 3 Fe/Al 2 O 3 . 11 In this study, we prepared mixed Ni–Fe catalysts by co- precipitation and further reduction of metal oxide precursors by hydrogen (50 vol.% H 2 in He, GHSV ¼ 100 ml/min) at 300 ○ C for 4 h. The resulting Ni–Fe catalysts were applied to the CH 4 production starting from CO 2 and H 2 , see details of preparation and characterization in Supplementary Information. Table 1 summarizes the specific surface (S sp ) and CH 4 /CO yields over the Ni–Fe catalysts against tem- perature. The activity of catalysts is found to be at the high stability level. Apart from CH 4 , CO is that reaction product which is usually observed in the composition of the outlet gas mixture. The formation of CO and CH 4 are interdependent. The higher yield of CH 4 caused the lower yield of CO and vice-versa. High CO 2 conversion (a sum of CH 4 /CO yields) and CH 4 selectivity (the ratio of CH 4 /CO yields) are noted at the temperature range from 300 ○ C to 400 ○ C. All catalysts are deactivated at and above 500 ○ C. Clearly, the highest yield of CH 4 (66.5%) gave the Ni 80 Fe 20 catalyst at 350 ○ C. In con- trast, pure Fe catalyst exhibits the highest selectivity to CO producing CH 4 only at and above 400 ○ C. The Ni metal and selected Ni–Fe catalysts always give rise to higher selectivity to CH 4 than to CO. Surprisingly, only Ni 75 Fe 25 catalyst provides an alternative reaction pathway to the reaction product CO, which is preferable over the methanation reac- tion below 500 ○ C. In this background, the production of CH 4 over Ni 90 Fe 10 and Ni 80 Fe 20 catalysts is comparably high. From the equilibrium Fe–Ni phase diagram, 12 the conversion should depend on the phase composition of a certain catalyst. The composition of the Ni 75 Fe 25 catalyst corresponds to a solid solution of Ni 3 Fe, 72–77 mass% Ni. At below 72 and above 77 mass% Ni, the biphasic Ni 3 Fe/γ-Ni region 12 can * Corresponding author. Functional Materials Letters Vol. 11, No. 3 (2018) 1850057 (4 pages) © World Scientific Publishing Company DOI: 10.1142/S1793604718500571 1850057-1