Abstract
Background: In the search of new catalysts for conversion of heavy naphtha fraction (C9+) into high octane number gasoline, metal modified ZSM-5 catalysts were investigated. The result revealed that modification ZSM-5 with metals (Ni, Fe, Zn) increased the C9+ fraction conversion and reduced the gas formation. In addition, hydrogen yield has increased the presence of Ni in the catalysts, whereas the number was reduced with other metals modification. Moreover, metal modified catalysts effectively prevented coke formation. Characterization studies (BET, XRD, TPR, TPD) results elucidated the effects of metals on catalytic performance. All the prepared catalysts possessed similar specific surface areas, thus the tuning of metallic sites was decisive for good catalyst performance. The combination of metallic sites (e.g. Ni) and acidic sites, supports all necessary reactions (e.g. cracking, aromatization, cyclization, alkylation, dehydrogenation, H-transfer) and thus helps to increase both heavy fraction conversion and reduces the coke formation. The finding might provide potential strategies for naphtha cracking.
Methods: Modified ZSM-5 catalysts with different metals were synthesized by hydrothermal crystallization method using TPABr (Sigma Aldrich) as a template. The prepared catalysts were evaluated for catalytic cracking of C9+ fraction of Vietnamese naphtha using a fully automated standardized Single Receiver – Short Contact Time - Microactivity Test. Then, catalysts characterization and catalytic performance were evaluated in order to verify the hypothesis and find out the useful strategies.
Results: In the present study, we reported an effective catalyst for cracking of heavy fraction of Vietnamese naphtha (C9+ fraction). The combination of metallic sites and acidic sites not only increase the conversion of heavy fraction into lighter fraction but also increase olefins and aromatics fraction in the gasoline. In addition, the modification with metals, especially with Ni would reduce the acidic sites of the modified catalyst and thus strongly prevent coke formation.
Conclusion: These findings might provide some valuable strategies for the development of effective catalysts for naphtha cracking and further uses reforming reaction in the simultaneous cracking and reforming. Such tests are now in progress.
Keywords: Selectively catalytic cracking, C9+ fraction, metal modified ZSM-5 catalysts, Vietnamese naphtha, catalyst metal.
Graphical Abstract
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