Research Projects

Plastic pollution is now one of the most pressing global environmental problems. Each year, approximately 400 million metric tons of plastics are produced, with 60% made up of polyolefins such as polyethylene and polypropylene. Unfortunately, around 80% of this plastic ends up in landfills or the ocean, as these materials are non-biodegradable. One of the most effective ways to upcycle plastics under mild conditions is through the hydrogenolysis of polyolefins using H₂. Despite recent progresses, catalytic hydrogenolysis of plastics faces many challenges, such as poor product selectivity, uncontrolled C‒C bond scission, the presence of multi-active sites and the usage of precious late-transition metal-based catalysts, which hinder the industrial viability of this technology. The objective of this proposal is to develop heterogeneous and single-site earth-abundant metal catalysts for a systematic and target-centric approach towards hydrogenolytic depolymerization of polyolefins and other plastics, such as polyethylene terephthalate (PET), into hydrocarbon fuels and other valuable chemicals under mild operational and environment-friendly conditions. We rationalize that the development of highly electrophilic, coordinatively unsaturated and single-site earth-abundant metal ions would efficiently cleave C‒C bonds either via σ-bond metathesis or β-alkyl transfer pathways. Furthermore, confining the electrophilic metal ion within porous materials having uniform and tunable pores, such as metal-organic frameworks (MOFs), will allow controlling the C‒C bond cleavage via size- or shape-selective hydrogenolysis. Following these designing principles, we propose to develop single-site earth-abundant metal catalysts using MOFs as crystalline, porous and tunable molecular materials for controlled depolymerization of polyolefins into commercially important short-chain liquid hydrocarbons. The proposed research first aims to synthesize a series of isoreticular MOFs node-supported highly electrophilic and coordinatively unsaturated single-site first-row transition metal hydride and alkyl species (Mn+-H/R; Mn+ = Ti4+, Zr4+, Fe3+, Co2+, Ni2+), which would efficiently cleave C‒C bonds either via σ-bond metathesis or β-alkyl transfer pathways (Objectives 1-2). We also plan to synthesize novel MOFs bearing strong electron-donor NNP- or NNN-pincer ligands at their linkers to develop electron-rich base-metal species within pores, which can cleave C‒C bonds via oxidative addition or by C‒H activation followed by β-carbon elimination (Objective 3). Following the synthesis, the materials will be tested as heterogeneous catalysts for hydrogenolysis of various plastics (LDPE, HDPE, polypropylene, polystyrene and PET) in a high-pressure batch reactor. The reactions will be systematically optimized by varying key parameters such as the pore sizes of MOFs, catalyst loading, temperature, and H₂ pressure to obtain the best selectivity and yield of liquid hydrocarbons (Objective 4). By tuning the pore sizes of the isoreticular MOFs, the distribution of the products will be systematically altered, affording different fuel-grade liquid hydrocarbons from polyolefins in high yields. Once developed, the most promising catalyst will undergo rigorous kinetic testing in a continuous flow reactor using a packed bed of the MOF-catalyst for a scale-up reactor design for commercial transformation of plastic waste into liquid fuel (Objective 5). We envision that our proposed MOF catalysts would enable highly efficient upcycling of plastic wastes owing to their unique combination of coordinatively unsaturated metal-active sites, confinement of well-defined active sites within uniform and tunable pores, well-defined porous structure, and superior stability via active site-isolation. Furthermore, the proposed research will also help educating our society about proper plastic usage and waste management and train students on plastic upcycling to tackle global plastic pollution.