多产芳烃并兼产小分子烷烃的正己烷转化机理

Conversion Mechanism of n-Hexane for High Yield of Aromatics and Concurrent Yield of Micromolecular Alkanes

对不同含量ZnO负载ZSM-5催化剂的物化性质和其催化正己烷芳构化反应性能进行了系统考察,利用分子模拟计算了关键反应步骤的能垒,对芳构化路径在不同阶段的变化进行了解释。结果表明:ZnO的引入强化了脱氢反应,从而提高了芳烃选择性,但过量的ZnO将加剧氢解反应,ZnO负载量以3%(质量分数)为宜;正己烷在3%ZnO/ZSM-5催化剂上的转化率小于58.02%时,生成芳烃的路径以脱氢反应为主;而转化率大于58.02%时,芳构化途径以氢转移为主,并且此时甲烷和乙烷的选择性由于氢解反应的发生而快速提高。分子模拟结果证实,氢解反应能垒较高,需在长的停留时间下才能发生,但该反应的发生不利于脱氢反应,进而导致芳构化途径的变化。该研究为正己烷芳构化多产芳烃并兼产小分子烷烃提供了理论依据。

The physicochemical properties and n-hexane aromatization performance of ZnO/ZSM-5 catalysts loaded with different amounts of ZnO were systematically investigated,the energy barriers of key reaction steps were calculated by molecular simulation,and the changes of aromatization paths at different stages were explained.The experimental results show that the introduction of ZnO strengthens the dehydrogenation reaction,thus improving the selectivity of aromatics.However,excessive ZnO will aggravate the hydrogenolysis reaction,and the appropriate loading amount of ZnO is 3%(mass fraction).When the conversion rate of n-hexane on 3%ZnO/ZSM-5 catalyst is lower than 58.02%,the main path to generate aromatics is dominated by dehydrogenation reaction;when the conversion rate is higher than 58.02%,the main path to generate aromatics is dominated by hydrogen transfer,during which the selectivities of methane and ethane are improved rapidly due to hydrogenolysis reaction.The molecular simulation results confirm that the hydrogenolysis reaction has a high energy barrier and requires a long residence time to occur;however,it is not conducive to the dehydrogenation reaction,which in turn leads to changes in the aromatization pathway.In conclusion,the study provides theoretical basis for the high yield of aromatics and concurrent yield of micromolecular alkanes obtained by the aromatization of n-hexane.