杂原子ZSM-5分子筛的合成、表征及其甲醇转化制烃类(MTH)催化性能

Synthesis and characterization of heteroatom ZSM-5 molecular sieves and their catalytic performance in methanol to hydrocarbon(MTH) reaction

配制相同比例凝胶,通过水热合成法制得三种杂原子ZSM-5分子筛(GaZSM-5、BZSM-5和ZnZSM-5)和一种AlZSM-5分子筛,经酸交换后压片成型制得催化剂。采用XRD、ICP、SEM、FT-IR、低温氮气吸脱附、NH3-TPD和Py-IR技术对其进行表征,并在连续流动固定床反应器上进行甲醇转化制烃类(MTH)反应性能评价。表征和评价结果表明,三种杂原子ZSM-5分子筛与AlZSM-5相比,催化剂酸强度降低、酸量减少和B酸与L酸比例得到不同调变,并对孔结构产生一定影响。GaZSM-5的酸量和酸强度降低,B酸比例居中,晶间介孔较大,提高了反应活性稳定性,催化剂寿命达到696h。BZSM-5的酸性弱,B酸比例高,外比表面积大,能够抑制积炭反应。ZnZSM-5的酸量少且酸性弱,B酸比例低,反应活性不足,但引入的锌中心极大提高芳烃选择性。

Three heteroatom ZSM-5 molecular sieves(Ga ZSM-5, BZSM-5 and Zn ZSM-5) and a Al ZSM-5 molecular sieve catalysts were prepared by hydrothermal synthesis method from the gels with the same molar ratio followed by acid exchange and pelletization.The samples were characterized by XRD, SEM, FT-IR, XPS, ICP, low temperature N2 physical adsorption and desorption, NH3-TPD and Py-IR, and their catalytic performances in the reaction of methanol to hydrocarbons(MTH) were evaluated in a continuous flow fixed bed reactor. The results showed that compared with Al ZSM-5, the heteroatom ZSM-5 molecular sieves weakened the acid strength, decreased acid number and changed the ratio of B/L and the pore structure. Ga ZSM-5 had appropriate acid amount and acid strength, suitable proportion of B acid and large crystal mesopore, which improved its catalytic stability, and its lifetime could reach 696 h. BZSM-5 had weaker acid strength, high proportion of B acid and larger external surface, which could inhibit coke deposition. Zn ZSM-5 with low acid content, weak acidity and low proportion of B acid had low reaction activity, but the introduction of zinc greatly enhance aromatics selectivity.