非金属元素改性ZSM-5分子筛催化甲醇制烯烃性能研究

Catalytic performance of nonmetallic ions modified ZSM-5 zeolites for methanol to light olefins

采用等体积浸渍法制备非金属元素改性催化剂P-ZSM-5、F-ZSM-5、B-ZSM-5,利用XRD、NH_(3-)TPD和N_2吸附/脱附分析催化剂的表面酸性和孔结构,测定各催化剂催化甲醇制低碳烯烃产物的选择性,并考察磷酸浓度对P-ZSM-5催化活性的影响。结果表明,ZSM-5分子筛经磷、氟改性后,催化剂的孔容和比表面积增大,表面强酸消失,烯烃选择性增大;经硼改性后,催化剂比表面积、孔体积显著减小,烯烃选择性降低。其中磷改性催化剂P-ZSM-5具有较大的孔容、比表面积和弱酸量,烯烃选择性最佳,在磷负载质量分数为6%时,乙烯+丙烯的选择性达85.09%,与ZSM-5相比,提高了22.7%。

P, F or B element modified ZSM-5 zeolites were prepared by incipient impregnation method, and characterized by XRD, N2-adsorption/desorption and NH3-TPD. Catalytic performances of the modified zeolites in the reaction of methanol to light olefins were tested, and the effect of （NH4）2HPO4 concentration on the catalytic activity of P-ZSM-5 zeolite was investigated. Results shows that modifying by P or F, the ZSM-5 zeolite improved its selectivity to light olefins that was due to the disappearing of surface stronger acid and the increase of pore volume and surface area of the ZSM-5 zeolite. However, the selectivity of light olefins de-creased when the ZSM-5 zeolite was modified by B that was due to the sharp decrease of pore volume. P-ZSM-5 exhibited larger pore volume, surface area and weaker acid sites, which made it had the best catalytic performance in methanol to light olefins reac-tion. The P-ZSM-5 （6%） had a ethylene＋propylene selectivity of 88.04%, increasing by 22.7%compared to the unmodified ZSM-5 zeolite.