天然气-二氧化碳-水蒸气-氧转化制合成气的研究——稀土助剂的作用

Study on Reforming Natural Gas-Carbon Dioxide-Steam-Oxygen to Syngas: The Role of Rare Earth Additives

研究了稀土氧化物 (CeO2 和La2 O3)改性的镍基催化剂中助剂的作用 ,并考察了催化剂对天然气 二氧化碳 水蒸气 氧转化制合成气反应的活性 .结果表明 ,La2 O3 改性的镍基催化剂具有较高的CH4 转化率和H2 选择性 ;经CeO2 改性的镍基催化剂具有较高的CO选择性 .量子化学计算和XRD研究结果表明 ,La2 O3 助剂的加入 ,可使还原后催化剂表面Ni(111)晶面衍射峰的强度减小 ,较好地符合吸附活化CH4 分子的“尺寸效应”和能量要求 .添加CeO2 助剂的催化剂 ,其Ni(111)晶面衍射峰强度较大 ,而Ni(110 )晶面含量最小 ,不利于CH4 的离解 .同时 ,助剂RE2 O3(尤其是CeO2 )和MgO提高了Ni的d电子密度 ,因而一定程度上加强了Nid电子向CO2 空反键π轨道的迁移 ,促进CO2 分子的活化 。

The role of rare earth additives (CeO2 and La2O3) in Ni-based catalysts has been investigated, and the activity and selectivity of the catalysts in reforming CH4-CO2-H2O-O-2 to syngas have been studied. The results show that the La2O3-promoted catalysts increase the conversion of CH4 and the selectivity for H-2. The results of quantum chemistry calculation and XRD demonstrate that the La2O3 additive can decrease the intensity of diffraction peak of Ni(111) crystal face of the reduced catalyst which makes its structure suitable for CH4 activation. The triodification of Ni-based catalysts by RE2O3 (CeO2) and MgO can increase d electron density of Ni and impel d electron to pi* orbit, thus CO2 is activated and its ability for carbon elimination is improved. The selectivity of the catalyst modified by CeO2 for CO is higher than that by La2O3.