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首页> 外文学位 >Synthesis, modification, characterization and catalytic studies of zeolite based bifunctional catalysts for hydroisomerization reactions.
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Synthesis, modification, characterization and catalytic studies of zeolite based bifunctional catalysts for hydroisomerization reactions.

机译：用于加氢异构化反应的沸石基双功能催化剂的合成，改性，表征和催化研究。

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Zeolite ZSM-12 was identified as a promising candidate for hydroisomerization of n-alkanes and a large part of the work was focused on the preparation of ZSM-12 and studying its catalytic performance. Reliable and efficient methods for synthesis of ZSM-12 with high levels of acidity were not available in the literature. Through systematic studies, the synthesis was greatly simplified and ZSM-12 was successfully crystallized at a relatively low Si/Al ratio of 30 using tetraethylammonium cations as the template. In the hydroisomerization of n-heptane as well as mixtures of n-alkanes, ZSM-12 catalysts provided a significantly higher selectivity to both monobranched and dibranched isomers, compared to other large pore zeolites. Kinetic studies carried out using individual octane isomers showed that the formation of certain dibranched and tribranched isomers was mildly hindered by the shape selective effect of the ZSM-12 pore, which resulted in the higher isomer yield.; It was found that the cracking activity of ZSM-12 could be increased by three to four times by carrying out the calcination to remove the template at temperatures higher than what is normally used. The variation of the cracking activity with respect to the calcination temperature was very unusual, only the samples calcined in two separate narrow temperature ranges showed substantially enhanced activity. Extensive FTIR characterizations, with pyridine adsorbed on the acidic zeolite, indicated that the enhancement in the cracking activity was due to a synergistic interaction between the framework Bronsted acid sites and a Lewis acidic extraframework aluminum (possibly cationic) species present in the zeolite. Hydroisomerization of n-heptane was studied over large pore zeolites with different acidity properties and wide range of Si/Al ratios. The performance of zeolite catalysts with enhanced activity were very sensitive to the platinum precursor used and the pretreatment conditions. The results suggested that zeolite acidity characteristics do not affect the isomer yield, provided the catalyst is carefully prepared to ensure good metal/acidity balance. Therefore, it appears that the only way to obtain isomer yields higher than that of Y zeolite is by employing shape selective zeolites.
机译：ZSM-12沸石被认为是正构烷烃加氢异构化的有前途的候选者，大部分工作集中在ZSM-12的制备和研究其催化性能上。在文献中没有可靠和有效的方法来合成高酸度的ZSM-12。通过系统研究，大大简化了合成过程，并使用四乙铵阳离子作为模板，以相对较低的Si / Al比30成功结晶了ZSM-12。在正庚烷以及正烷烃混合物的加氢异构化过程中，与其他大孔沸石相比，ZSM-12催化剂对单支链和二支链异构体的选择性明显更高。使用单独的辛烷异构体进行的动力学研究表明，ZSM-12孔的形状选择效应对某些二支和三支异构体的形成有轻微的阻碍，从而导致更高的异构体收率。发现通过在高于通常使用的温度下进行煅烧以除去模板，ZSM-12的裂化活性可以提高三至四倍。裂解活性相对于煅烧温度的变化是非常不寻常的，仅在两个单独的窄温度范围内煅烧的样品显示出显着增强的活性。吡啶分子吸附在酸性沸石上的广泛FTIR表征表明，裂解活性的提高是由于骨架布朗斯台德酸位与沸石中存在的路易斯酸性骨架外铝（可能是阳离子）物种之间的协同相互作用。研究了正庚烷的加氢异构化反应在具有不同酸度特性和宽范围Si / Al比的大孔沸石上的应用。具有增强活性的沸石催化剂的性能对所用的铂前体和预处理条件非常敏感。结果表明，只要精心制备催化剂以确保良好的金属/酸度平衡，沸石的酸度特性就不会影响异构体的收率。因此，似乎获得比Y型沸石更高的异构体产率的唯一方法是采用形状选择型沸石。

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