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

Abstract

Hydrogenolysis of C–C bonds over Ru-based catalysts has emerged as a deconstruction strategy to convert single-use polyolefin waste to liquid alkanes at relatively mild conditions, but this approach exhibits limitations, including methane formation resulting from terminal C–C bond scission. In this study, a variety of catalysts were investigated for the reductive deconstruction of polyethylene (PE) and polypropylene (PP) to identify supports that promote nonterminal C–C bond scission. We found that Ru nanoparticles supported on Brønsted-acidic zeolites with the faujasite (FAU) and Beta (BEA) topologies were highly active for the cleavage of C–C bonds in PE and PP, exhibiting improved liquid yields and suppressed methane formation. For the deconstruction of PE, supporting ruthenium nanoparticles (5 wt %) on FAU increased the yields of liquid alkanes to 67% compared to 33% over an inert silica support (5 wt % Ru/SiO2) at 200 °C, 16 h, under 30 bar of H2. A dramatic selectivity enhancement toward liquid hydrocarbons was also observed for PP over Ru/FAU and Ru/BEA compared to Ru/SiO2. To understand the origin of this selectivity improvement, a combination of ex situ and operando characterization techniques were used to reveal that both catalyst structure and acidity play key roles in PE and PP conversion. Operando X-ray absorption spectroscopy studies with model polyolefins over Ru-supported catalysts with varying acidity levels revealed that the local chemical environment of Ru[0] during the reaction is consistent across multiple acidic supports, although the onset of reduction during synthesis of the nanoparticles varies across different supports. These results, combined with reactivity data, demonstrate the importance of the acid-noble metal cooperativity in promoting selective C–C bond scission toward liquid alkanes that shifts the mechanism from hydrogenolysis to ideal hydrocracking.

Enhanced Production of Liquid Alkanes from Waste Polyethylene via the Electronic Effect‐Favored Csecondary−Csecondary Bond Cleavage

“…On the contrary, Ru/CeO 2 ‐O with more metallic Ru species favors the adsorption of terminal C primary to undergo the terminal C secondary −C primary bond cleavage to produce methane. It should be mentioned that besides the electronic effect, the Ru particle size would affect the cleavage positions in the hydrogenolysis of PE and liquid alkanes [5,11a,25] …”

“…The imbalance between the massive production of plastics and the plastic waste management has led to a global ecological crisis and considerable attention has been paid to plastic upcycling recently. [1][2][3][4][5] Polyethylene (PE) is the most consumed plastic and accounts for about 40 % of plastic production. [6] Towards PE upcycling, chemical transformation is considered to be a promising method to convert waste PE into more desirable short-chain alkanes.…”

“…The imbalance between the massive production of plastics and the plastic waste management has led to a global ecological crisis and considerable attention has been paid to plastic upcycling recently [1–5] . Polyethylene (PE) is the most consumed plastic and accounts for about 40 % of plastic production [6] .…”

Zeolite Supported Pt for Depolymerization of Polyethylene by Induction Heating

“…For example, the k in Table 2 at 285 °C surface temperature is more than 20 times that for a hydrogenolysis/aromatization process that does not use H 2 at 280 °C (Table 3). 9 It is even comparable to polyolefin depolymerization processes that do use H 2 , greater than the derived k's for catalytic processes making alkanes at 250 8 and 200 °C, 48 while slightly less than a k for a different catalyst making lubricants at 300 °C, 12 all in Table 3. Obtaining this high a reaction rate and still a relatively narrow product distribution, without the use of any added H 2 , shows that the combination of IH with Pt−Sn zeolites is a powerful one for LDPE depolymerization.…”

Catalytic hydroconversion processes for upcycling plastic waste to fuels and chemicals

“…Recently, Yury and his co-workers demonstrated Ru supported on FAU or BEA zeolites as active catalysts for the hydrocracking of polyethylene and polypropylene waste to liquid products with a yield up to 67%. 39 Based on the ex situ and operando studies with model small hydrocarbons, they claimed that the dispersion of Ru metallic particles and the acidity properties rather than Ru reducibility play key roles in the conversion of polyolefins by hydrocracking.…”