Efficient and Selective Low-Temperature Polypropylene Hydrogenolysis Using Zr-Doped Mixed Metal Oxides Catalysts

Abstract The thermal catalytic hydrogenolysis of polyolefins offers a pathway to convert plastic waste to value-added hydrocarbons. However, the reliance on noble metals such as Ru or Pt remains a significant barrier to large-scale implementation. In this work, we demonstrate that the Zr-containing mixed metal oxides (MMOs), Co0.7Al0.3–xZrx (CAZ), Ni0.7Al0.3–xZrx (NAZ), and Ni0.7Co0.3–xZrx (NCZ), with x = 0, 0.1, 0.2, and 0.3, are highly effective at 250 °C under 20 bar of H2 for virgin isotactic polypropylene (PP) (Mw = 240 kDa) hydrogenolysis to give liquid hydrocarbon products. The catalysts were produced by calcination of the Zr-containing layered double hydroxide (LDH) precursors; [Co0.7Al0.3–xZrx(OH)2][CO3](0.3–x)/2, [Ni0.7Al0.3–xZrx(OH)2][CO3](0.3–x)/2, [Ni0.7Co0.3–xZrx(OH)2][CO3](0.3–x)/2; x = 0, 0.1, 0.2, and 0.3. This approach allowed us to exploit the compositional tunability of the LDH framework to control the homogeneous distribution of the active metal centers. We find that Zr incorporation in these MMOs can significantly enhance catalytic PP hydrogenolysis. Our best-performing catalysts, Co2.1Al0.3Zr0.6Oy, delivers, after 1 h at 275 °C and 20 bar of H2, liquid hydrocarbon yields above 75% at a total PP conversion of over 90%, while keeping methane yields below 3%. Mechanistic studies show that these catalysts favor backbone C–C cleavage, delivering C3, C6, and C9 hydrocarbon selectivity. These scalable, highly efficient, and cost-effective catalysts are also efficient for the hydrogenolysis of a mix of commercial PP products. Hydrogenolysis of mixed pipette tips using Co2.1Al0.3Zr0.6Oy (275 °C, 1.5 h, 20 bar H2) produced a liquid hydrocarbon yield of 74%.