含杂原子硼ZSM-5分子筛的合成及对甲醇脱氢制甲醛的催化性能

Synthesis of boron-containing ZSM-5 molecular sieves and their catalytic performance in methanol dehydrogenation to formaldehyde

以水热合成法及混合研磨法制备含杂原子硼的ZSM-5分子筛,采用XRD、N2吸附-脱附、FT-IR、UV-Vis、11B MAS NMR、NH3-TPD和SEM等方法对其进行表征,在连续流动常压固定床反应器上考察两种方法制备的分子筛对甲醇脱氢制甲醛反应的催化性能并进行对比。结果表明,水热合成法的B-ZSM-5分子筛中的硼原子主要以四配位的形式存在于分子筛骨架中,研磨法制备的B/ZSM-5分子筛的硼原子主要以三配位的形式存在于骨架外。硼原子的存在状态显著影响分子筛的酸性、比表面积、孔道结构和形貌等物化性能,从而影响甲醇脱氢制甲醛的催化性能。在n(Si)∶n(B)=7.5和反应温度550℃条件下,水热合成法的B-ZSM-5分子筛对甲醇的转化率为62.97%,甲醛选择性为68.86%。混合研磨法制备的B/ZSM-5分子筛对甲醇的转化率为47.26%,甲醛选择性为57.72%。

The boroncontaining ZSM5 molecular sieves were prepared by hydrothermal synthesis, and grinding methods and were characterized by XRD, N2 adsorptiondesorption, FTIR, UVVis, n B MAS NMR, NH3TPD and SEM. The catalytic performance of the two kinds of molecular sieves for methanol de hydrogenation to formaldehyde was investigated in a fixedbed flow reactor. The experimental results indi cated that boron atoms in fourcoordination mainly existed in the framework of BZSM5 molecular sieve prepared by hydrothermal method, while tricoordinated boron atoms existed in framework external of B/ZSM5 molecular sieve prepared by grinding method. Existence state of boron atoms remarkably affect ed the acidity, specific surface area, pore structure and surface appearance of the molecular sieves, thus affected their catalytic performance in methanol dehydrogenation to formaldehyde. Under the condition of n（Si）：n（B） =7.5 and reaction temperature 550 ℃ ,the conversion of methanol and the selectivity to formaldehyde were 62.97% and 68.86% respectively over BZSM5 molecular sieve prepared by hydro thermal method. On B/ZSM5 molecular sieve prepared by grinding method, methanol conversion and the selectivity to formaldehyde were 47.26% and 57.72%, respectively.