Supported Platinum Nanoparticles Catalyzed Carbon-Carbon Bond Cleavage of Polyolefins: Role of the Oxide Support Acidity.

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.