CO methanation over Ni/γ-Al_2O_3 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(wNi = 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.