Adsorption and ring-opening of lactide on a chiral metal surface studied by Density Functional Theory

TL;DR

This study uses Density Functional Theory to analyze lactide adsorption and ring-opening on a chiral Pt(321) surface, revealing low energy barriers, potential for low-temperature catalysis, and enantioselectivity effects.

Contribution

It provides the first detailed DFT analysis of lactide ring-opening on a chiral metal surface, highlighting catalytic activity and chiral selectivity.

Findings

Ring-opening energy barriers are around 0.3 eV.

Adsorption energies are approximately 1.4 eV.

Reaction occurs at very low temperatures with enantioselectivity.

Abstract

We study the adsorption and ring-opening of lactide on the naturally chiral metal surface Pt(321)$^S$. Lactide is a precursor for polylactic acid ring-opening polymerization and Pt is a well known catalyst surface. We study here the energetics of the ring-opening of lactide on a surface that has a high density of kink atoms. These sites are expected to be present on a realistic Pt surface and show enhanced catalytic activity. The use of a naturally chiral surface also enables us to study potential chiral selectivity effects of the reaction at the same time. Using Density Functional Theory (DFT) with a functional that includes the van der Waals forces in a first-principles manner, we find modest adsorption energies of around 1.4 eV for the pristine molecule and different ring-opened states. The energy barrier to be overcome in the ring-opening reaction is found to be very small at 0.32 eV and 0.30 eV for LL- and its chiral partner DD-lactide, respectively. These energies are much smaller than the activation energy for a dehydrogenation reaction of 0.78 eV. Our results thus indicate that (a) ring-opening reactions of lactide on Pt(321) can be expected already at very low temperatures and Pt might be a very effective catalyst for this reaction; (b) the ring-opening reaction rate shows noticeable enantioselectivity.