RETRACTED: Hydrogenolysis of Polyethylene and Polypropylene into Propane over Cobalt-Based Catalysts

Abstract

The development of technologies to recycle polyethylene (PE) and polypropylene (PP), globally the two most produced polymers, is critical to increase plastic circularity. Here, we show that 5 wt % cobalt supported on ZSM-5 zeolite catalyzes the solvent-free hydrogenolysis of PE and PP into propane with weight-based selectivity in the gas phase over 80 wt % after 20 h at 523 K and 40 bar H2. This catalyst significantly reduces the formation of undesired CH4 (≤5 wt %), a product which is favored when using bulk cobalt oxide or cobalt nanoparticles supported on other carriers (selectivity ≤95 wt %). The superior performance of Co/ZSM-5 is attributed to the stabilization of dispersed oxidic cobalt nanoparticles by the zeolite support, preventing further reduction to metallic species that appear to catalyze CH4 generation. While ZSM-5 is also active for propane formation at 523 K, the presence of Co promotes stability and selectivity. After optimizing the metal loading, it was demonstrated that 10 wt % Co/ZSM-5 can selectively catalyze the hydrogenolysis of low-density PE (LDPE), mixtures of LDPE and PP, as well as postconsumer PE, showcasing the effectiveness of this technology to upcycle realistic plastic waste. Cobalt supported on zeolites FAU, MOR, and BEA were also effective catalysts for C2–C4 hydrocarbon formation and revealed that the framework topology provides a handle to tune gas-phase selectivity.

Role of Bifunctional Ru/Acid Catalysts in the Selective Hydrocracking of Polyethylene and Polypropylene Waste to Liquid Hydrocarbons

“…In a recent study, Zichittella et al reported that zeolite ZSM-5 alone was active for PE and PP hydrocracking at 250 °C over 20 h in 40 bar H 2 , although the addition of Co nanoparticles promoted stability and selectivity . To rule out the possibility that FAU and BEA supports alone are contributing to the high hydrocracking activity under the reaction conditions reported here, a series of control reactions were performed in the absence of ruthenium nanoparticles.…”

Catalytic hydroconversion processes for upcycling plastic waste to fuels and chemicals

“…Besides heterogeneous Ru- and Pt- based catalysts for the hydrogenolysis of POs, other supported non-noble metal catalysts, such as Zr-, 60 Ni-, 61 Co- 62 and Nb- 63 based catalysts, have been demonstrated to be effective for the transformation of POs into valuable alkanes.…”

“…The Co/HZSM-5 catalyst was reported for the solvent-free hydrogenolysis of LDPE, PP, mixtures of LDPE and PP, and postconsumer PE into propane with a selectivity of 80 wt% in the gas phase at 280 °C, 4 MPa H 2 for 20 h of reaction. 62 The ZSM-5 zeolite support was found to be an important host for the stabilization of dispersed oxidic cobalt nanoparticles, as well as preventing further reduction to the metallic state which is the site for CH 4 generation. In addition, the C 2 –C 4 hydrocarbon gas-phase selectivity can be tuned by using zeolites with different framework topologies, such as FAU, MOR and BEA.…”

“…To further improve the catalyst activity, the same group tuned the catalyst's electronic properties by modifying the synthesis using ammonia. 55 60 Ni-, 61 Co- 62 and Nb-63 based catalysts, have been demonstrated to be effective for the transformation of POs into valuable alkanes.…”

Site-Selective Polyolefin Hydrogenolysis on Atomic Ru for Methanation Suppression and Liquid Fuel Production

“…However, over 85% of waste polyolefins are dumped in landfills or disposed of in environmentally harmful ways (e.g., incineration), contradicting the global sustainability efforts since polyolefin is another form of fossil energy [ 8 – 10 ]. The catalytic hydrogenolysis reaction has been developed to convert polyolefins into value-added liquid fuels under mild conditions efficiently [ 11 – 16 ]. The H 2 -rich system promotes the hydrogenation of cracked intermediate to form alkanes and suppresses the coke deposition [ 17 ].…”