Abstract
Polyolefin plastics are the most popular polymer materials worldwide, and the catalytic degradation of post-consumer polyolefins has attracted increased attention as a viable process. In this study, two types of Ni-based catalysts supported on Hbeta zeolite, Ni-Hbeta and NiS(2)-Hbeta, have been successfully synthesized for the hydrocracking of waste polyolefin. The experimental results indicated that the synergistic effect between Ni or NiS(2) and the acidic sites of Hbeta zeolites can significantly enhance the tandem cracking and hydrogenation of polyolefin plastics, which suppresses the formation of gas products and coke. Ni-Hbeta employed as a catalyst can effectively degrade HDPE into high value liquid and gas products with high yield of 94% under 523 K and 3 MPa H(2), while also exhibiting excellent cycle stability. In particular, Ni-Hbeta shows better catalytic performance than NiS(2)-Hbeta during the hydrocracking of HDPE at a relatively low temperature of 523 K. Furthermore, Ni-Hbeta catalyst also exhibits a remarkable capability for efficient depolymerization of unsorted post-consumer polyolefin plastics (HDPE, LDPE, PP) containing various additives and pollutants. These findings underscore the application potential of employing noble metal-free and recyclable catalysts for hydrocracking plastic waste, thereby facilitating the realization of a circular economy for plastics.