Although the mass production of synthetic plastics has transformed human lives, it has resulted in waste accumulation on the earth. Here, we report a low-temperature conversion of polyethylene into olefins. By mixing the polyethylene feed with rationally designed ZSM-5 zeolite nanosheets at 280 °C in flowing hydrogen as a carrier gas, light hydrocarbons (C₁-C₇) were produced with a yield of up to 74.6%, where 83.9% of these products were C₃-C₆ olefins with almost undetectable coke formation. The reaction proceeds in multiple steps, including polyethylene melting, flowing to access the zeolite surface, cracking on the zeolite surface, formation of intermediates to diffuse into the zeolite micropores, and cracking into small molecules in the zeolite micropores. The ZSM-5 zeolite nanosheets kinetically matched the cascade cracking steps on the zeolite external surface and within micropores by boosting the intermediate diffusion. This feature efficiently suppressed the intermediate accumulation on the zeolite surface to minimize coke formation. In addition, we found that hydrogen participation in the cracking process could hinder the formation of polycyclic species within zeolite micropores, which also contributes to the rapid molecule diffusion. The coking-resistant polyethylene upcycling process at a low temperature not only overturns the general viewpoint for facile coke formation in the catalytic cracking over the zeolites but also demonstrates how the polyethylene-based plastics can be upcycled to valuable chemicals. In addition to the model polyethylene, the reaction system worked efficiently for the depolymerization of multiple practically used polyethylene-rich plastics, enabling an industrially and economically viable path for dealing with plastic wastes.

中文翻译：

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沸石微孔扩散调控的耐结焦聚乙烯升级循环

尽管合成塑料的大量生产改变了人类的生活，但也导致了地球上的废物堆积。在这里，我们报告了将聚乙烯低温转化为烯烃的过程。通过将聚乙烯原料与合理设计的 ZSM-5 沸石纳米片在 280 °C 下以流动的氢气作为载气混合，以高达 74.6% 的产率生产轻烃 (C ₁ -C ₇ )，其中 83.9%产品为 C ₃ -C ₆几乎检测不到焦炭形成的烯烃。反应分多个步骤进行，包括聚乙烯熔化、流动进入沸石表面、在沸石表面裂解、形成中间体以扩散到沸石微孔中以及裂解成沸石微孔中的小分子。ZSM-5 沸石纳米片通过促进中间扩散在动力学上匹配沸石外表面和微孔内的级联裂化步骤。这一特征有效地抑制了沸石表面上的中间体积累，从而最大限度地减少了焦炭的形成。此外，我们发现氢参与裂解过程可能会阻碍沸石微孔内多环物质的形成，这也有助于分子的快速扩散。低温下的抗结焦聚乙烯升级循环工艺不仅颠覆了沸石催化裂化过程中容易形成焦炭的普遍观点，而且还展示了聚乙烯基塑​​料如何升级循环为有价值的化学品。除了模型聚乙烯之外，该反应系统还可以有效地解聚多种实际使用的富含聚乙烯的塑料，从而为处理塑料废物提供了一条工业上和经济上可行的途径。