Composite oxide supported Ni-based catalysts were prepared by a wet impregnation technique and applied to the methanation of carbon dioxide. The composite oxide supports were prepared by an impregnation−precipitation method using commercial γ-Al 2 O 3 powder as a host with variation of the percentage of loading of ZrO 2 , TiO 2 , and CeO 2 promoters from their respective salt precursors. NH 4 OH was used as the precipitating agent. The as-prepared catalysts were characterized by Brunauer−Emmet−Teller surface area analysis, atomic absorption spectroscopy, X-ray diffraction, temperature-programmed reduction by H 2 (H 2 -TPR), and CO chemisorption. Catalytic activity of the newly synthesized catalysts was investigated toward hydrogenation of CO 2 at atmospheric pressure by varying reaction temperature between 250 and 400 °C (with increasing step equal to 25 °C). Experimental results revealed that the composite oxide supported Ni-based catalysts showed performance superior to that of the γ-Al 2 O 3 only supported Ni-based catalyst (which was synthesized using the same procedure for comparison). Among the investigated catalysts, the Ni/C15 catalyst with composite oxide support (55% of γ-Al 2 O 3 loading and 15% equivalent loading of ZrO 2 , TiO 2 , and CeO 2 ) showed the best activity: 81.4% conversion of CO 2 to CH 4 at 300 °C. Better performance of the composite oxide supported Ni-based catalysts was achieved because of the improvements in the reducibility nature of the catalysts (investigated using H 2 -TPR).

Two nickel−aluminum hydrotalcite samples (HTLCs) were prepared by a coprecipitation method at different pH values and investigated as catalysts for the hydrogenation of carbon dioxide. The newly synthesized samples have been compared with a reference alumina supported nickel-based commercial catalyst, with equal nickel content. The as-prepared and commercial samples were characterized by BET analysis, atomic adsorption spectroscopy (AAS), X-ray diffraction (XRD), and temperatureprogrammed techniques (H 2 -TPR and CO-TPD). Catalytic activity of the analyzed samples was investigated toward hydrogenation of CO 2 at atmospheric pressure by varying reaction temperature between 250 and 400 °C. The maximum CO 2 -to-CH 4 conversion value achieved by hydrotalcyte was ≈86% at 300 °C. The superior performance of HTLCs has been put in relationship with the major catalysts reducibility nature and with the higher metal surface area and metal dispersion. The stability of the HTLCs was investigated through long-term tests, resulting in good stability in the reported reaction conditions.

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