摘要
改进甲烷水蒸汽转化催化剂的抗析炭性能,降低生产中所用的水碳比,可以大量节约能耗。这是近年来国内外重视的研究课题。 热力学分析指出,在甲烷水蒸汽眨应中存在CH_4裂解、CO歧化和CO的氢还原三个析炭反应。但在工业上现用的较高水碳比下(3.0～4.0),析炭以CH_4裂解为主,而其余两个反应表现为逆反应为主,即脱炭反应。动力学研究表明。
The effect of the addition and the sequence of addition of RE2O3 (heavier rare earth oxides) on the properties of adsorbed H2O, activities for CH4 cracking and reaction of deposited carbon with steam of CH4-H2O reforming catalysts was studied by temperature programmed desorption of the adsorbed H2O. temperature programmed cracking of methane, temperature programmed surface reaction of deposited carbon with steam and X-ray diffraction. As compared with NiO/ Al2O3, the dispersion of both NiO and Ni for NiO-RE2O3/Al2O3 (prepared by the addition of RE2O3 prior to NiO)was increased. The total amount of adsorbed H2O and the maximum reaction rate of deposited carbon with steam at 240℃ enhanced 35% and 192% respectively, and the maximum cracking rate of CH4 increased 14% at 530℃. As compared with NiO/Al2O3, the maximum cracking rate of CH4 for RE2O3-NiO/Al2O3 (prepared by the addition of NiO prior to RE2O3) obviously dropped by 39% at 517℃. The maximum reaction rate of deposited carbon with steam enhanced 82% at 255℃, but only a little change in the dispersion of both NiO and Ni and in the amount of adsorbed H2O was observed. The resistance to carbon deposition of NiO catalyst is improved in either case, but their mechanism is different. The mechanism of NiO-RE2O3/Al2O3 is mainly due to the increase of the amount of adsorbed H2O, and that of RE2O3 -NiO/Al2O3 is due to the decrease of CH4 cracking rate.
