(116c) Effect of Chain Branching on the Hydrogenolysis of Heptane Isomers over Metal Catalysts: Insights to Hydrogenolysis of Polyethylene.

The ever-increasing rate of production of plastics, most especially single-use plastics, have plagued our world with significant amounts of pollutants due to the limitations in plastics recycle. This has spurred the interests of researchers to design catalysts that selectively upcycle plastic wastes into value-added materials. One of the major techniques being studied is the catalytic hydrogenolysis. Due to the similarities in the chemical structure and relative inertness of alkanes and polyethylene, which accounts for most plastics produced, it has been suggested that the same mechanism may guide their hydrogenolysis.

In this work, we investigated and compared the mechanism of the hydrogenolysis of linear and several branched isomers of heptane over Pt(111) and other Pt surfaces to smaller hydrocarbons and intermediates, using density functional theory (DFT) calculations. As claimed by previous work on alkane hydrogenolysis, we found that C-C bond activations have to be preceded by a series of dehydrogenation steps, which reduces their degree of saturation and allow for Carbon-Metal bonding. In the absence of dehydrogenation steps, C-C bond cleavage has a high energy barrier.

Next, we performed a mean-field microkinetic model for the hydrogenolysis of heptane isomers to establish reaction pathways, determine the rate for each elementary step, and determine the rate controlling step. Finally, we are in the process of developing models for extrapolating information from alkanes to the hydrogenolysis of polyethylene chains.