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Susannah ScottDept. of ChemistryUniversity of CA – Santa Barbara
The use of polyolefins to make small molecules, not limited to monomers which can be repolymerized, is an intriguing approach to recycle carbon and thereby keep plastic out of the natural environment. While catalytic hydrogenolysis leads to lower value alkanes, hydrogen redistribution in the absence of added H2 can achieve tandem hydrogenolysis and dehydrocycloaromatization, resulting in higher value aromatics at moderate reaction temperatures. The coupled reactions are greatly accelerated by the use of bifunctional hydrocracking catalysts whose acidity can be used to tune the selectivity towards surfactant-range alkylaromatics. The key rate-determining and selectivity-controlling steps are shown to involve Brønsted acid catalysis. Other tandem processes, including the selective conversion of polyethylene to monomers under mild reaction conditions, can be designed to achieve alternative desired reaction outcomes.