Effect of Metal Catalyst Facets on Polyethylene Adsorption

Catalytic conversion provides a path for tackling the
global problem
of plastic waste handling. The product distributions depend on the
location of C–C scission on a catalyst, and thus on the conformation
of the polymer on the catalyst surface. However, the effects of catalyst
surface morphology on polymer melt adsorption are not well understood.
Here, we study Pt surfaces of different terminations and polymers
of varying chain sizes to probe the impact of terrace width on polyethylene
(PE) conformations on the catalyst surface. We parametrize an atomistic
force field using density functional theory calculations and perform
replica-exchange molecular dynamics simulations on the PE-catalyst
systems. We find that the surface morphology alters the conformations
of PE. Stepped surfaces favor shorter adsorbed segments but more such
segments adsorb per chain. They also induce more ordering in the adsorbed
segments than the flat surface, which has implications for the ability
of mean-field models to describe polymer adsorption on surfaces and
their subsequent reactions. The smaller chains, earlier believed to
be entirely adsorbed on the surface, do not do so on stepped surfaces.
We discuss the ramifications of these findings for the hydrogenolysis
of PE on catalyst metal nanoparticles.