Ab Initio Molecular Dynamics investigation of the Coadsorption of Acetaldehyde and Hydrogen on a Platinum Nanocluster

By means of ab initio molecular dynamics, we have investigated the molecular adsorption of acetaldehyde on Pt 13 nanoparticles in the presence of coadsorbed hydrogen on the surface of the metal particle. The acetaldehyde molecules exclusively interact with low-coordinated metal atoms of the nanoparticle while they remain inert toward direct interaction with adsorbed hydrogen, thus confirming the key role of the metal as intermediate binding site for hydrogenation. At room temperature within a time scale of picoseconds aldehyde-metal bonds are formed. Coadsorbed hydrogen decreases the reactivity of the aldehyde molecules toward the metal. Kinetically, the first adsorption modes to occur are of the eta(1) type, either via the oxygen or via the carbon atom. A tendency for double adsorption on the same metal site is observed. Upon addition of ammonia molecules to the simulation box, the interesting phenomenon of the conversion of eta(1) to eta(2) carbonyl bonding appears, mediated by the adsorption of the ammonia nitrogen to a platinum atom. This investigation highlights the richness of the interaction modes of a carbonyl group with a platinum nanoparticle, reached in the very brief time scale of a few picoseconds. In particular the adsorption modes of the aldehyde are modified by the presence of a second electron-donor molecule, such as another aldehyde molecule or an ammonia molecule, in the latter case even changing the adsorption mode of the carbonyl moiety from eta(1) to eta(2).