A Broad-Spectrum Catalyst for Aliphatic Polymer Breakdown

Thermolysis of the well-defined aluminum fluoroalkoxide supported on silica (≡SiOAl(OC(CF₃)₃)₂(O(Si≡)₂), 1, 0.20 mmol_Al g^-1) at 200 °C forms a fluorinated amorphous silica-alumina (F-ASA) containing a distribution of Al(IV), Al(V), and Al(VI) sites that maintain relatively strong Lewis acidity. Small amounts of Brønsted sites are also present in F-ASA. Solid-state NMR studies show that a majority of the aluminum centers in F-ASA are not close to the Si-F groups that form during thermolysis. F-ASA is exceptionally reactive in cracking (or pyrolysis) reactions of neat polymer melts. Catalyst loadings as low as 2 wt % (0.017 mol % aluminum) efficiently break down isotactic polypropylene, high-density polyethylene, ethylene/1-octene copolymer, and postconsumer wastes. The major products of this reaction are hyperbranched liquid paraffins containing internal olefins and very small amounts of aromatics. Under continuous distillation of oils from the reaction mixtures, pyrolysis on 50 g reaction scales is feasible. F-ASA cokes and deactivates during this reaction but can be reactivated by calcination in air. These properties are complementary to other state-of-the-art catalysts for polymer breakdown, but unlike those catalysts F-ASA does not require an additional cofed reactant (e.g., H₂, olefin, etc.) to drive the reaction.