Effects of support composition on the performance of nickel catalysts in CO2 methanation reaction

The CO2 methanation reaction was studied over catalysts containing different amounts of nickel (10-40 wt.%), prepared by the impregnation of alumina, zirconia and ceria supports with aqueous solutions of nickel nitrate and citric acid. It was found that the nickel content did not have a strong influence on the porosity and specific surface area of the respective catalysts. The reducibility of the catalysts decreased in order Ni-CeO2 > Ni-ZrO2 > Ni-Al2O3. High activation temperature was required for alumina supported catalysts. The active surface area of alumina supported catalysts increased with an increase of nickel loading. In contrary, the decrease of the active surface area with an increase of nickel content was observed for zirconia supported catalysts. Hydrogen temperature-programmed desorption studies indicated that the nature of nickel surface sites was influenced by the metal-support interactions. An increase in reduction temperature of CeO2 supported catalysts led to a pronounced increase of mean nickel crystallite size and a decrease of the active surface area. Alumina supported catalysts revealed high resistance against sintering. The catalysts showed high activity and selectivity to methane at low reaction temperatures (200-300 degrees C). Gradual increase in CO2 conversion with an increase of Ni loading was observed for alumina supported catalysts. Such effect was less evident for ceria and zirconia supported catalysts. Ceria supported catalysts, in spite of lower active surface area showed higher activity than alumina supported catalysts. In-situ Diffuse Reflectance Fourier Transform Infrared spectroscopy studies underlined the influence of the support composition on the course of surface reactions in CO2 methanation.