Adsorption of Acrolein, Crotonaldehyde, and Cinnamaldehyde on Pt(111) Surfaces: A Comparative DFT Study

Using ab initio calculations, we have investigated the adsorption of both S-cis and S-trans isomers of acrolein, crotonaldehyde, and cinnamaldehyde on the Pt(111) surface at low and high surface coverages and for five types of coordinations. Emphasis was placed on identifying trends by highlighting the similarities and differences in the adsorption of all three molecules. Adsorption was found to depend on coverage: the most stable adsorption geometry at low coverages is flat, in either eta(3) or eta(4) coordinations with most atoms bonded to the surface, whereas a more tilted arrangement involving fewer atoms, in a eta(2)-C2C3 coordination mode, prevails at high coverages. The extra methyl group in crotonaldehyde was determined to lead to a destabilization of the multiply coordinated adsorbates at high coverages, whereas the aromatic ring in cinnamaldehyde was found to be able to bind itself to the Pt surface, at least at low coverages, and thus increase the absolute value of the adsorption energy by about 0.5 eV. Additional calculations using a noncovalent interaction index provided further insights into the variations in bonding to the surface across the three molecules versus coverage in terms of both covalent and noncovalent attractive and repulsive interactions.