不同硅铝比Co／ZSM-5催化剂对费托合成汽油馏分烃选择性的调控

摘要

以ZSM-5分子筛为载体，通过等体积浸渍法制备了Co／ZSM-5系列催化剂，用于费托合成反应一步法制汽油馏分烃（C5～C11烷烃）。考察了不同硅铝比（SiO2／Al2O3＝25，38，50，80和200）的ZSM-5分子筛对Co／ZSM-5催化剂费托合成汽油馏分选择性的影响。采用氮气物理吸附-脱附、X射线衍射、氢气程序升温还原（H2-TPR）和氨气程序升温脱附（NH3-TPD）等手段对载体和催化剂进行了表征，并在高压固定床反应器上对催化剂的费托合成催化性能进行了测试。结果表明，对比Co／ZSM-5（SiO2／Al2O3＝25，38，50和80）催化剂，Co／ZSM-5（SiO2／Al2O3＝200）催化剂表现出最高的汽油馏分烃类选择性，高达52．8％，这主要归功于Co／ZSM-5（SiO2／Al2 O3＝200）催化剂上较小钴颗粒尺寸、较优的还原性能以及适量弱酸位的协同作用。分子筛的酸性为催化剂的加氢裂解转化提供活性位，促进重质烃产物发生裂解和异构等二次反应，较小的钴颗粒尺寸和较优的还原性能有利于提高C5＋烃选择性。%One-step gasoline synthesis from syngas via Fischer-Tropsch synthesis (FTS)reaction was in-vestigated on Co/ZSM-5 (SiO2/Al2O3 =25,38,50,80 and 200)catalysts.The Co/ZSM-5 catalysts were prepared by impregnation method using cobalt nitrate solution in ZSM-5 with varied SiO2/Al2 O3 ratio and characterized by BET,XRD,H2-TPR and NH3-TPD.The Fischer-Tropsch synthesis activity tests were car-ried out in a fixed-bed reactor.The results showed that the Co/ZSM-5 (SiO2/Al2 O3 =200)was found to be superior to the other Co/ZSM-5 catalysts in terms of better gasoline selectivity (C5 ~C11 fraction)due to the formation of small cobalt particles and the presence of larger number of weak acidic sites.It also ex-hibited the highest catalytic activity because of the higher reducibility and the smaller cobalt particle size.