Ethane and Propane Dehydrogenation on Small Platinum Clusters Supported on Silica: An Ab Initio Molecular Dynamics and DFT Study.

Abstract

The size-dependent activity of catalysts has been researched for a long time in the field of catalysis. Positively charged small Pt clusters enhance catalytic activity than bigger clusters and bulk for propane dehydrogenation. We performed DFT calculations on small Pt clusters adsorbed on silica support. The planar structure of Pt clusters is present till 4 Pt atoms, after which three-dimensional structures are observed. AIMD and DFT calculations for silica showed that it has a high surface area and thermal stability suitable to conduct dehydrogenation reactions. The adsorption of Pt cluster on silica results in the formation of directional bonds which affects the properties of the adsorbed Pt catalysts by changing the redox properties. In the bulk phase, ethane and propane molecules undergo dehydrogenation reactions with 0.133 eV atom-1 and 0.244 eV atom-1 energies, respectively. NEB calculations showed that except for Pt-2/SiO2 , all the even Pt clusters require less activation energy than the neighboring odd Pt clusters. Ethane molecule interacting with Pt-4/SiO2 , Pt-5/SiO2 , Pt-6/SiO2 , and propane with Pt-3/SiO2, Pt-4/SiO2 , Pt-5/SiO2 , Pt-6/SiO2 , follows the reverse Horiuti-Polanyi mechanism during dehydrogenation, whereas non-reverse Horiuti-Polanyi mechanism (which requires comparatively lower activation energy) is followed for smaller Pt clusters.