Single-use plastic waste pollution will cause significant harm to the environment if left unaddressed. One possible mitigation strategy is to develop processes, e.g. catalytic hydrogenolysis, that can convert (i.e. upcycle) waste plastics into value-added products capable of participating in a circular economy. Platinum (Pt) catalysts on strontium titanate nanocuboid supports (STO; Pt/STO) are attractive hydrogenolysis catalysts because of properties such as cube-on-cube epitaxy between Pt and STO, which contribute to superior catalytic performance. However, for Pt/STO to commercially upcycle discarded polyolefins, tunable and scalable Pt/STO syntheses that do not harm catalytic performance must be designed. As part of a broad upcycling study, Pt/STO catalysts were synthesized by scalable methods and used to hydrogenolyze research-grade polyethylene into uniform, straight-chain lubricant products (Mn = 490 Da, Ð = 1.03). Microwave- and convection-based STO nanocuboid syntheses were developed to control support particle size and morphology, and highly cuboidal STO nanoparticles were obtained with average sizes from 20 to 80 nm and low size variance between the particles in each batch. One synthesis produced 20 g STO under relatively mild conditions (16 h, 200 °C) and replaced TiCl4 (l) with titanium (IV) bisammonium lactato dihydroxide, a water-stable Ti4+ complex. Pt nanoparticles were deposited on STO using surface organometallic chemistry (SOMC) and strong electrostatic adsorption (SEA). For both techniques, sequential cycles of deposition and reduction were used to increase Pt loading on the support surface. For SOMC-derived Pt/STO, average loading increased up to 1.5 % Pt by weight, and average Pt particle size increased to about 1.5 nm. For SEA-derived Pt/STO, average loading increased to 0.65 % Pt by weight, and average Pt particle size increased to about 2.8 nm. SOMC-derived Pt/STO converted isotactic polypropylene (starting Mn = 6000 Da) into low-dispersity products (Ð = 1.1 for each sample) with average molecular weights centered between 200 < Mn < 300 Da. Increasing the scale of Pt/STO synthesis did not adversely affect upcycling product distributions when said catalysts were used for hydrogenolysis. Consistent with experimental observations, preliminary models of polymer adsorption on Pt/STO via a united-atom representation suggest that long chains adsorb preferentially on Pt.

Creator

• Peczak, Ian Lukasz

DOI

• https://doi.org/10.21985/n2-ze4y-jp93

Subject

• Chemistry
• Materials Science

Language

• en

Alternate Identifier

• http://dissertations.umi.com/northwestern:16513
• etdadmin_upload_983506

Date created

• 2023-01-01

Resource type

• Dissertation

Rights statement

• In Copyright