CO methanation over Ni/γ-Al₂O₃ catalysts with different morphologies

 NiO with different morphologies were prepared by precipitation method and then the NiO/γ-Al₂O₃ catalysts were prepared from NiO and γ-Al₂O₃ by grind-mixing method. These catalysts were characterized by means of TEM, XRD and H₂-TPR techniques. TEM images show that the morphologies of three NiO phases (a-NiO, b-NiO and c-NiO) obtained are in the shape of rod, granule and sheet, respectively. H₂-TPR profiles show that the oxidabilities of these catalysts are in the order of b-NiO/γ-Al₂O₃ < a-NiO/γ-Al₂O₃ < c-NiO/γ-Al₂O₃. XRD patterns show that the crystalline sizes of Ni in these catalysts after reduction are in the order of b-Ni > a-Ni > c-Ni. CO methanation was carried out over the Ni/γ-Al₂O₃ catalysts in a continuous flow fixed-bed reactor and the effects of mixing method and morphology of active species on the catalysts performance were investigated. It is found that the catalyst prepared from grind-mixing exhibits higher activity and stability than that obtained from simple-mixing. The catalytic activities of these catalysts with different morphologies for CO methanation follow the order of c-Ni/γ-Al₂O₃ > a-Ni/γ-Al₂O₃ > b-Ni/γ-Al₂O₃. Over the c-Ni/γ-Al₂O₃ catalyst (w_Ni = 15%) under the conditions of atmospheric pressure, 593K and a space velocity of 2500h^-1, the conversion of CO and the selectivity to CH₄ reach 99.63% and 90.80%, respectively.