Alleviating the global plastic waste crisis requires closed-loop chemical recycling, in which monomers are recovered from end-of-life plastics via an efficient chemical process. Current polyolefin (PO) depolymerization technologies demand high temperatures and pressures and yield uncontrolled mixtures of products limited to single-use waxes, oils, and greenhouse gas emitting fuels. Heterogenous superacids, defined by Hammet Acidity Functions (H0) ≤ –12 (i.e., stronger than 100% H2SO4), like sulfated zirconia (SZrO), are industrially deployed catalytic platforms capable of activating hydrocarbons under mild thermal conditions. Toward an efficient PO depolymerization process, we have meticulously investigated SZrO. Preliminary evidence has verified bulk SZrO’s ability to decompose POs at atmospheric pressures and temperatures &lt; 200 °C. However, as we began to synthesize SZrO, we made a startling realization: Despite 30 years of combined catalytic engineering and industrial use, the atomic-level chemistry of SZrO is poorly understood. The historical, deployment-driven study of this superacid has left significant knowledge gaps surrounding SZrO’s synthesis, structure, and catalytic behavior. A leading misconception is that SZrO’s acid strength purely stems from a Brønsted or Lewis acid site. In contrast, we hypothesize that SZrO’s superacidity arises from cooperation between Lewis acid sites (coordinatively unsaturated Zr(IV) atoms), which polarize the C–H bonds of reactants toward the H-atom, and Brønsted acid sites (sulfates), which protonate the reactant’s hydride to release H2 and induce carbenium formation. Ideally, successive β-scissions of olefins down the PO chain could allow the generation of a renewable hydrocarbon feedstock. Minute differences in SZrO’s synthetic conditions (thermal treatments, sulfation, support materials and other additives, etc.) drastically alter the relative expression of Brønsted and Lewis acidity, leading to mischaracterization and misuse of a highly valuable industrial catalyst. Defining the synthesis and structure of SZrO may unveil novel developments in catalysis, including an avenue toward the efficient recycling of polyolefins.

Defining the synthesis and structure of sulfated zirconia toward the low temperature and pressure depolymerization of polyolefins

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