Our group has employed RF-induction heating (RF-IH) methods to break down plastics over dual-functional Fe3O4 and Ni- or Pt-based zeolite and metal oxide catalysts. We generated high concentrations of alkene/alkane hydrocarbons, with relatively narrow product distributions. An RF-IH-driven process offer several benefits over traditional thermal heating routes, in particular, a large interface/bulk temperature gradient (so only the polymer in the vicinity of the catalyst particles reaches reaction temperatures), and the apparent inhibition of some secondary reactions (low amounts of methane, aromatics and coke are produced). At a surface temperature of 420°C , a catalyst to polymer ratio of 1: 10 and no added H2, a maximum conversion of 82 wt.% was obtained in 2h with 0.5 wt% Pt/K-MFI. However, the liquid products only accounted for 2% of the total conversion by weight, the remaining being mostly gaseous products, with 0.3 wt% coke formation. Now we demonstrate that for PE depolymerization, with RF-IH and a bifunctional (Pt- or Pt-Sn containing) catalyst and varying the type of zeolite support, we can obtain even higher hydrocarbon product yields (up to 95 wt % in 2 h) at a lower surface temperature (375 °C), and with a tunable product distribution ranging from light gas products to gasoline- to diesel-range hydrocarbons. Four zeolite types [MFI, LTL, CHA(SSZ-13), TON] were chosen as the supports due to their varying pore sizes and structures. These depolymerization results are again obtained at atmospheric pressure and without use of H2. We are working to understand how Pt, with or without Sn, on zeolite supports differing in pore geometry, can affect product selectivity, activity, and coke formation in the depolymerization reactions. To this end we have employed a variety of surface characterization (XANES, XAFS, XPS, STEM, TPO) techniques to analyze fresh and spent catalysts. We also demonstrate how RF-IH helps overcome diffusional resistances associated with conventional thermal heating and thereby shortens reaction times.

Zeolite supported Pt and Pt-Sn catalysts for depolymerization of polyethylene by RF-induction heating

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