ZnHZSM-5上丙烷芳构化的研究─丙烷的活化

研究了HZSM－5、ZnHZSM－5和ZnNaZSM－5上的羟基振动光谱和一氧化碳吸附的红外光谱，以及丙烷的芳构化反应．红外光谱中发现表征强B酸的3610cm－1羟基振动峰相对强度由于锌离子的引入和浸渍氢氧化钠而减小，说明了锌离子和钠离子均进入了分子筛的阳离子位；一氧化碳在锌离子上的吸附峰位在2232cm－1，说明进入阳离子位的锌离子是一种强L酸．反应结果表明，锌离子的引入大大地促进了丙烷的转化和芳烃选择性的提高；在一定范围内，随浸渍氢氧化钠量的增加，丙烷转化率下降，而丙烯的选择性和产率增加，说明了锌组份直接参与了丙烷的脱氢过程．Zn－L酸是丙烷活化脱氢的中心，丙烷在该中心上异裂活化直接脱氢．

The Study of Propane Aromatization over ZnHZSM-5: Activation of Propane

The IR spectra of hydroxyl and probe molecule CO and the aromatization of propane were investigated over HZSM-5, ZnHZSM-5 and ZnNaHZSM-5.The IR spectra showed that the relative band intensity of strong acidic hydroxyl groups at 3610cm-1 decreased by Zn2 ion exchange and sodium hydroxide impregnatin,which indicated that Zn2 and Na cations had occupied the cation centers in the zeolite.The band appearing at 2232cm-1 in CO IR spectra demonstrated that Zn2 cations were a sort of strong lewis acid. The greatly improvement of propane conversion and aromatics selectivity after Zn2 incorporation into HZSM-5, the decreasing of propane conversion and the increasing of propane selectivity and yield from sodium hydroxide impregnation depicted that zinc species directly participate in propane dehydrogenation. In conclusion,zinc lewis acid sites are the activation centers for propane dehydrogenation, on which propane could be hetero-cracking activated and directly dehydrogenated.