CO and CO₂ Methanation Over Ni/γ-Al₂O₃ Prepared by Deposition-Precipitation Method.

Various Ni catalysts supported on γ-Al₂O₃ were prepared by a wet impregnation (WI) method and deposition-precipitation (DP) method with different precipitants and applied to CO and CO₂ methanation. The prepared catalysts were characterized by various techniques including nitrogen physisorption, X-ray diffraction (XRD), temperature-programmed reduction with H₂ (H₂-TPR), H₂ chemisorption, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Irrespective of kinds of precipitant, the Ni/γ-Al₂O₃ catalysts prepared with a DP method showed a remarkable enhanced catalytic performance in CO and CO₂ methanation compared with the Ni/γ-Al₂O₃ catalyst prepared with a WI method owing to the higher catalytic active surface area (CASA). In the case of Ni/γ-Al₂O₃ catalysts prepared with a DP method, the high calcination temperatures are not favorable for the high catalytic activity due to the decreased reduction degree of Ni oxide species and CASA. The reduction degree of Ni oxide species can be increased with reduction temperature. However, the higher reduction temperature above 500 °C is not desirable to achieve the high catalytic activity because of the decreased CASA. The selective CO methanation was also accomplished at lower temperatures over the Ni/γ-Al₂O₃ catalyst prepared with a DP method than over the Ni/γ-Al₂O₃ catalyst prepared with a WI method.