The current scale of plastics production and the accompanying waste disposal problems represent a largely untapped opportunity for chemical upcycling. Tandem catalytic conversion by Pt/g-Al₂O₃ converts various polyethylene grades in high yields (up to 80 wt%) to low molecular-weight liquid/wax products, in the absence of added solvent or H₂, with little production of light gases. The major components are valuable long-chain alkylaromatics and alkylnaphthenes (average ca. C₃₀, Ð = 1.1). Coupling exothermic hydrogenolysis with endothermic aromatization renders the overall transformation thermodynamically accessible despite the moderate reaction temperature of 280 °C. This approach demonstrates how waste polyolefins can be a viable feedstock for the generation of molecular hydrocarbon products.

Note for DSC

DSC measurements were performed on a Mettler Toledo Polymer DSC instrument and analyzed using the STARe software. Each polymer sample (approx. 5 mg) was placed in a crimped aluminum pan. Using a heating/cooling rate of 10 °C/min, the samples were heated from -70 to 200 °C under a flow of N₂, cooled to -70 °C, then heated to -200 °C. The crystallization temperature (T_c) and the melting temperature (T_m) were obtained from the first cooling and second heating cycles, respectively.

Note for “Regression analysis for Figure 5b.nb”

This dataset is the Mathematica 12.0 notebook for the model fit presented in Figure 5b. The data used in this model fit is presented in Table S3. The Mathematica file performs the model fit and plots the experimental data, model fit, and confidence bands on the model fit. Fit parameters are also reported.

Note for GPC characterization:

Molecular weight distributions of the starting PE or the hydrocarbon products were analyzed on an Agilent PL-GPC 220 gel permeation chromatograph, equipped with a PL-Gel Mixed B guard column, three PL-Gel Mixed B columns, and a refractive index (RI) detector. Samples were dissolved in 1,2,4-trichlorobenzene (TCB) containing di-tert-butylhydroxytoluene (BHT, 0.01 wt%), by heating at 150 °C for at least 1 h. Elution was achieved using TCB (with BHT) at 150 °C and 1.0 mL min^-1. The molecular weight response was calibrated with monomodal, linear polyethylene standards (Varian). To ensure accurate measurement of low molecular weight materials (M_w <1000 g mol^-1), PE standards with peak molecular weights M_p of 507 and 1180 g mol^-1 (Polymer Standards Services) were included in the calibration. All the data was analyzed using the Agilent Cirrus software.Selected product mixtures were also analyzed by GPC with UV detection. Analysis was conducted on a Waters 2690 HPLC equipped with two Agilent Columns (PLgel, 5μm MiniMIX-D, 250×4.6 mm) and a guard column (MW linear range 200 - 400,000 g/mol), a Waters 2410 refractive index (RI) detector and a Waters 2998 photodiode array detector (PDA). Chloroform with 0.25 vol% triethylamine was used as the mobile phase at room temperature and 0.35 mL/min. Calibration was achieved using polystyrene standards (Agilent EasiVial kit, linear response for the range 200 < molecular weight < 400,000 g/mol).The data were processed in the Waters Empower software.

Note for NMR characterization:

¹H NMR spectra of the starting PE were recorded in bromobenzene-d5 at 80 °C using a Varian Unity Inova 500 MHz spectrometer. Spectra of the productswere recorded in 1,1,2,2-tetrachloroethane-d2.1H NMR spectra were acquired at 600 MHz on a Varian Unity Inova AS600 spectrometer. Chemical shifts (δ, ppm) were calibrated using the residual proton signals of the solvent and referenced to tetramethylsilane (TMS). All data were processed using MestReNova (v11.0.1, Mestrelab Research S. L.) to correct the baseline and phase of each spectrum. 

¹³C NMR spectra were acquired on a Bruker AVANCE III Ultrashield Plus 800 MHz (18.8 T) spectrometer. A Bruker TXI HCN cryoprobe was used to enhance sensitivity for direct 13C detection. 13C spectra were recorded using a long relaxation delay (10 s) to ensure quantitative intensities. All data were analyzed using Topspin (v4.0.6, Bruker Biospin). The baseline of the raw spectra was processed by a linear prediction method.  Detailed processing method see attached “13C-NMR method for linear prediction on baseline.doc” file.

Note for GC-FID:

Hydrocarbons in the gas fraction (C₁-C₉) were analyzed quantitatively on a Shimadzu GC-2010 gas chromatograph equipped with a capillary column (Supelco Alumina Sulfate plot, 30 m x 0.32 mm) and a flame ionization detector (FID). Propene was added as an internal standard. Relative carbon response factors were assumed to be 1.0. The injector and detector temperatures were 200 °C. The temperature ramp program was: 90 °C (hold 3 min), ramp 10 °C /min to 150 °C (hold 20 min). All the data and PDF reports were generated by GCsolutions, Shimadzu Corporations software. Hydrocarbons in the liquid fraction (C₆-C₃₀) for C30 experiment or violate fraction (C6-C10) for some PE test were quantitatively analyzed on an Agilent 6890N Network gas chromatograph equipped with an Agilent DB-5 capillary column (fused silica, 30 m x 0.25 mm x 0.25 µm) and FID. The inlet and detector temperatures were 300 and 280 °C, respectively. The temperature ramp program was: 40 °C (hold 3 min), ramp 25 °C /min to 320 °C (hold 10 min). The flow rate was 1.0 mL/min (He) with a split ratio of 5:1. The data was processed by the instrument using the Agilent OpenLab CDS ChemStation (product version. A.01.04).

Note for GC-TCD:

H₂ was quantified on a Shimadzu GC-8AIT gas chromatograph equipped with a packed column (ShinCarbon ST 80/100, 2 m x 2 mm) and a thermal conductivity detector (TCD), using Ar as the internal standard. The linear response of the TCD signal to the injected volume of H₂ and Ar was confirmed using standard H₂/Ar gas mixtures. The response factors for H₂ (f_H2) and Ar (f_Ar) were obtained as the slopes of fitted lines. The column, injector and detector temperatures were 130 °C. The TCD current: 70 mA and the head pressure were 300 kPa (N₂). GC-TCD result was collected by GC-solutions, Shimadzu Corporations and was converted in CSV files through OpenChrome software. In CSV files, column headers are listed in the first row of each column.

Note for FD-MS:

Spectra were obtained on a Waters Micromass GCT Premier Time of Flight mass spectrometer, operating with an extraction rod voltage of 12 kV. Samples were dissolved in dichloromethane and loaded directly onto a CARBOTEC FD emitter, consisting of a 10 µm tungsten wire carrying a pyrocarbon coating of microneedles (ca. 120 µm diameter). Nominal mass data were acquired while employing a data-dependent ramp of the emitter current from 0-90 mA, pausing the ramp when more than 30 counts per scan were observed in the base peak ion. The extraction rods were cleaned between acquisitions by slowly raising the extraction rod current to 3 A while maintaining a 12 kV charge. The emitter was cleaned between acquisitions by raising the emitter current to 95 mA for 5 s. The calibration range is 400 < m/z < 1200, with a maximum mass error of 0.2 m/z. A mixture of triacontane (C₃₀H₆₂), and 1,4-didodecylbenzene (C₃₀H₅₄) in a molar ratio of 1:1.02 was analyzed to assess sensitivity and accuracy for detecting and quantifying different types of hydrocarbons. Each compound gave its molecular ion as the major peak. The similar peak heights confirm that this data is suitable for the semi-quantitative analysis of their relative abundance. The MassLynx program is used to acquire date and for all aspects of data processing. In order to compute selectivities, the FD-MS signal was filtered to assign each peak to a certain series through a python code (attached file “Expt-3-liquid-FD-MS-mass picking method”). The filtered signal (peak height) was then interpolated and integrated to compute the relative total response of each series.

Note for “Regression analysis for Figure 5b.nb” 

A working copy and basic understanding of Mathematica 12.0 is required to run this file. The file is commented with explanations of the functions used. The derivation of the function used for the model fit is presented in the supporting information (eq. S10-S35). Only the data from Table S3 is used for model fitting, and the necessary portions of Table S3 are reproduced in this file.