Supported Platinum Nanoparticles Catalyzed Carbon–Carbon Bond Cleavage of Polyolefins: Role of the Oxide Support Acidity
Jessica V. Lamb, Yu‐Hsuan Lee, Jia‐Kai Sun, Carly Byron, Ritesh Uppuluri, Robert M. Kennedy, Chao Meng, Ranjan Kumar Behera, Yiyu Wang, Long Qi, Aaron D. Sadow, Wenyu Huang, Magali Ferrandon, Susannah L. Scott, Kenneth R. Poeppelmeier, Mahdi M. Abu‐Omar, Massimiliano Delferro
Abstract
Supported platinum nanoparticle catalysts are known to convert polyolefins to high-quality liquid hydrocarbons using hydrogen under relatively mild conditions. To date, few studies using platinum grafted onto various metal oxide (M x O y ) supports have been undertaken to understand the role of the acidity of the oxide support in the carbon–carbon bond cleavage of polyethylene under consistent catalytic conditions. Specifically, two Pt/M x O y catalysts (M x O y = SrTiO 3 and SiO 2 –Al 2 O 3; Al = 3.0 wt %, target Pt loading 2 wt % Pt ∼1.5 nm), under identical catalytic polyethylene hydrogenolysis conditions ( T = 300 °C, P(H 2 ) = 170 psi, t = 24 h; M w = ∼3,800 g/mol, M n = ∼1,100 g/mol, Đ = 3.45, N branch/100C = 1.0), yielded a narrow distribution of hydrocarbons with molecular weights in the range of lubricants ( M w = < 600 g/mol; M n < 400 g/mol; Đ = 1.5). While Pt/SrTiO 3 formed saturated hydrocarbons with negligible branching, Pt/SiO 2 –Al 2 O 3 formed partially unsaturated hydrocarbons (<1 mol % alkenes and ∼4 mol % alkyl aromatics) with increased branch density ( N branch/100C = 5.5). Further investigations suggest evidence for a competitive hydrocracking mechanism occurring alongside hydrogenolysis, stemming from the increased acidity of Pt/SiO 2 –Al 2 O 3 compared to Pt/SrTiO 3 . Additionally, the products of these polymer deconstruction reactions were found to be independent of the polyethylene feedstock, allowing the potential to upcycle polyethylenes with various properties into a value-added product.