Evaluation of two approaches for the synthesis of hierarchical micro-/mesoporous catalysts for HDPE hydrocracking
Plastic waste management has become a pressing global issue. A viable and sustainable alternative to incineration is the conversion of polyethylene into chemicals or fuels by through hydrocracking. To improve the catalytic performance during hydrocracking, bifunctional catalysts are required, in which the zeolite imparts the acid function, and the metallic function is provided by a noble or transition metal, such as nickel. In this study, acid supports were synthesized using two strategies, namely zeolitisation and desilication, for comparison. The synthesized materials exhibited Si/Al molar ratios of approximately 10, hierarchical micro-/mesoporosities, and a bifunctional character after incorporation of nickel up to 5 wt%. The materials were extensively characterized by various techniques, including powder X-Ray diffraction, N2 sorption, acidity measurement, and scanning electron microscopy. The characterization results showed that the desilicated HZSM5 zeolite was the most effective support for nickel impregnation, leading to a quantitative conversion of High-Density Polyethylene (HDPE) by hydrocracking and the formation of predominantly hydrocarbons with 5 carbon atoms. A clear disparity in composition, with a prevalence of a gasoline-type fraction, was observable in the liquid phase from HZSM5 to Ni particles supported on hierarchical HZSM-5 (Ni@m-HZSM-5w). The hierarchy factor (HF), the molar ratio between Lewis and Brønsted acid sites, and the accessibility factor (ACI) were combined to form the interplay factor (IF). The investigation resulted in materials with IF values between 0.35 and 7, and a positive correlation between HDPE conversion and IF values is observed. In conclusion, this study suggests that the desilication of HZSM5 zeolite is a promising route for the development of efficient catalysts for the hydrocracking of plastic waste.
Dr. Sabino Armenise and Dr. Wong Syie Luing, have received support from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant Agreement No. 754382, GOT ENERGY TALENT. Dr. Armenise want to dedicate special thanks to Sorbonne University and to all research department of Cepsa who help to characterize the catalysts and to C. Prieto, J. Frontela, B. Aramburu and R. Larraz to support this postdoctoral research. This research has been carried out during the postdoctoral position at URJC-CEPSA. Funding from Fundação para a Ciência e Tecnologia, Project UIDB/00100/2020, Project UIDP/00100/2020 and Project LA/P/0056/2020 is also gratefully acknowledge. The publication is part of the TED2021-129688B project, funded by MCIN/AEI/10.13039/501100011033 and by the European Union "NextGenerationEU"/PRTR. The content of this publication does not reflect the official opinion of the European Union. Responsibility for the information and views expressed in this paper lies entirely with the authors.
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