不同形貌Ni/γ-Al2O3催化剂催化CO甲烷化反应的研究

采用沉淀法分别以乙二醇、水、乙二醇-聚乙二醇600为修饰剂，制备了形貌分别为棒状（a-NiO）、粒状（b-NiO）和片状（c-NiO）结构的NiO催化剂，然后和γ-Al₂O₃通过研混法制得NiO/γ-Al₂O₃催化剂。采用XRD、TEM及H₂-TPR等技术手段对催化剂进行了表征。TEM观察NiO的形貌分别为棒状、粒状和片状。H₂-TPR结果表明,NiO/γ-Al₂O₃催化剂的氧化中心数量顺序为b-NiO/γ-Al₂O₃＜a-NiO/γ-Al₂O₃＜c-NiO/γ-Al₂O₃。XRD结果表明，NiO/γ-Al₂O₃催化剂还原后的Ni晶粒尺寸大小为b-Ni＞a-Ni＞c-Ni。在连续流动固定床反应装置上考察了Ni/γ-Al₂O₃对CO甲烷化反应的催化活性，研究了混合方法和形貌对CO甲烷化反应的影响。结果表明，研混法制得催化剂的活性及稳定性较好。催化剂形貌对CO甲烷化反应的催化活性顺序为c-Ni/γ-Al₂O₃＞a-Ni/γ-Al₂O₃＞b-Ni/γ-Al₂O₃，常压、593K和2500h^-1反应条件下，w_Ni为15% c-Ni/γ-Al₂O₃催化CO合成CH₄选择性及CO转化率分别达90.80%和99.63%。

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.