Pt enhanced C-H bond activation for efficient and low-methane-selectivity hydrogenolysis of polyethylene over alloyed RuPt/ZrO2

Catalytic hydrogenolysis of polyethylene (PE) to liquid alkanes has drawn broad attention due to its high efficiency in the degradation of the largest fraction of plastic wastes. However, the reaction mechanism and the origin of methane selectivity are still ambiguous. Here, we demonstrate that the activation of C-H bonds has a great influence on both the activity and selectivity of polyethylene hydrogenolysis. By introducing Pt with high C-H bond activation efficiency into the monometallic Ru/ZrO2 catalyst, the alloyed RuPt/ZrO2 catalyst was successfully synthesized and various characterizations, including HAADF-STEM, EXAFS and H-2-TPR, elucidated the structure of the RuPt alloy. Compared with the monometallic Ru/ZrO2 catalyst, the RuPt alloy can enhance the activation of the C-H bonds in the polyethylene chain, thus consequently improving the cleavage of C-C bonds. Surprisingly, the methane selectivity is greatly inhibited on the RuPt alloy. Isotopic TPSR and density functional theory (DFT) calculations reveal that the RuPt alloy has excellent C-H activation capability, the hydrogenolysis rate can be accelerated by promoting the first C-H activation, which is harder on monometallic Ru. Furthermore, the RuPt alloy is more effective in activating internal C-H bonds compared to monometallic Ru, avoiding terminal C-C cleavage generating methane. Additionally, the hydrogenation of intermediates is enhanced on the RuPt alloy, preventing sequential deep dehydrogenation and C-C bond cleavage, ultimately reducing methane formation. This work indicates that the activation of C-H bonds is of great significance for polyethylene hydrogenolysis, which provides a catalyst-designing strategy for polyethylene hydrogenolysis that is more valuable and efficient.