轻烃在改性ZSM－5催化剂上转化成芳烃与低碳烯烃的选择性控制

研究了Ｃ３－Ｃ９烷烃在不同的改性ＺＳＭ－５沸石上的反应规律．过渡金属离子改性的ＺＳＭ－５沸石显示了较高的芳烃选择性，芳烃的选择性还取决于改性金属离子的脱氧能力并可通过预硫化得到改进．钾、钡改性的沸石显示了较高的烯烃选择性，增加钾含量，烯烃选择性显著提高，但也明显抑制了催化剂的活性；提高Ｂａ含量，同样可提高烯烃选择性，但对活性影响不大．环己烯的模型反应结果表明，Ｋ，Ｂａ的作用在于抑制了双分子氢转移反应和提高了脱氢能力．红外表征结果表明，沸石表面的羟基，因不同金属改性而发生不同的变化．此外，气相氧对提高烯烃和芳烃的收率有明显作用

DIRECTIONAL CONTROL OF THE CONVERSION OF LIGHT PARAFFINS TO AROMATICS AND LIGHT OLEFINS OVER MODIFIED ZSM 5

The conversion of C 3 C 9 paraffins over ZSM 5 modified by various metal cations has been investigated. Transition metal cations modified ZSM 5 zeolite catalysts exhibit higher selectivity for aromatics, which can also be improved by pre sulfidation of ZSM 5. Meanwhile K or Ba cation modified ZSM 5 zeolite catalysts show high selectivity for light olefins and the selectivity increases with increasing K or Ba loading. The conversion decreases sharply with increasing K loading, but keeps at high level with increasing Ba loading. The results of cyclohexene reaction on the K or Ba modified catalysts have shown that the dehydrogenation activity is enhanced and the H transfer reaction activity is inhibited. There are different surface OH groups on ZSM 5 modified by the two kinds of metal cations as studied by FT IR spectra. Both the reaction of light paraffins and selectivity for aromatics and light olefins can be improved by adding dioxygen in the feed. Therefore, the reaction path of aromatization and dehydrogenation of light paraffins or dehydrocracking of paraffins on ZSM 5 zeolite can be controlled by incorporating different metal cations, which also lead to different surface OH groups as evidenced by IR spectra. The activation and selective conversion can be promoted by dioxygen in feed or by presulfidation of ZSM 5 zeolite.