Oxidizability and catalytic properties of Platinum nanoclusters: unraveling the role of cluster size and type of supporting surface

This work presents a systematic computational investigation over oxidation and potential catalytic performance of Pt nanoclusters supported on two different metal oxides. Ab initio calculations were performed based on Density Functional Theory. Pt nanoclusters in the present work consisted of a few Pt atoms and were simulated both on gas-phase and supported on the surface of brookite TiO2(210) and Co3O4 (111). First, the oxidation of free-standing and supported Pt clusters for different sizes was investigated. Gas-phase and supported clusters were found to be more prone to oxidation compared to bulk Pt. A size-dependent oxidation trend was predicted for Pt clusters as smaller cluster was easier to oxidize, independent of the type of support. The same size-dependent oxidation trend was found for gas-phase and supported Pt clusters. Next, the oxidation of CO was modeled on Pt clusters to examine the catalytic performance of these systems. Prior to modeling the reaction, we employed the ab initio thermodynamics to find the possible oxidation degree of the clusters at the reaction condition. Our calculations showed that from the thermodynamics standpoint, in finite temperature and pressure of oxygen and carbon monoxide, clusters would be partially oxidized regardless of the type of the support. However, the kinetic studies on partially oxidized clusters revealed that they would almost reduce to a more metallic catalyst. Then, we focused on modeling the CO oxidation reaction on metallic clusters and single atom Pt. To this end, Langmuir-Hinshelwood and Mars-Van Krevelen oxidation mechanisms were simulated on different sizes of Pt catalysts over titanium and cobalt oxide. On brookite, single atom Pt catalysts, whether anchored on the surface or substituting an atom from the surface lattice, exhibited lower activation energy for converting CO into CO2 . The predicted activation energy was found to be higher on the larger Pt cluster, and smaller cluster performed even weaker. On the other hand, single atom Pt on Co3O4 was not predicted to be an active catalyst, both in anchored state or substituting an atom from the surface. Doped Co3 O4 with single atom Pt was found to be ac- tive catalyst only. This implies the key role of the type of supporting surface in the catalytic properties of the catalyst. By comparing two oxidation mechanisms on Pt clusters, we concluded that the L-H mechanism is more probable on Co3O4 supported Pt clusters rather than TiO2 . However, the MvK mechanism seems to be a more facile oxidation mechanism on adsorbed Pt catalysts on TiO2 .