386434 Catalyst/Support Interactions Between Pt Nanoparticles and Amorphous Silica

Wednesday, November 19, 2014
Galleria Exhibit Hall (Hilton Atlanta)
Christopher S. Ewing1, Michael J. Hartmann2, Surya Padinjarekutt2, Allison M. Musto2, Elliott M. Weiss1, Kaitlin R. Martin1, Daniel S. Lambrecht2, Götz Veser1, Joseph J. McCarthy1 and J. Karl Johnson1, (1)Chemical & Petroleum Engineering, University of Pittsburgh, Pittsburgh, PA, (2)Chemistry, University of Pittsburgh, Pittsburgh, PA

Metal nanoparticles (NPs) play a key role in catalysis due to large surface-to-volume ratios and low-coordination active surface sites. These catalysts are typically immobilized on oxide supports to suppress sintering, which leads to catalyst deactivation and degradation of catalyst selectivity. An atomistic understanding of catalyst systems is essential to the rational design of improved catalyst systems. Catalyst activity and selectivity are highly dependent on shape and size of NPs as well as the nature of the oxide support. Despite significant advancement of experimental characterization techniques, a detailed understanding of the catalyst-support interface for very small NPs (~ 1 nm or smaller) is largely precluded by experimental investigations. Computational methods provide one means to overcoming this challenge. In previous studies catalyst supports have generally been either neglected or treated as highly ideal structures, however, oxide supports are often used in an amorphous state, exhibiting a wide range of surface sites.

Due to its thermal stability and tunable porosity, and hence specific surface area, amorphous silica is widely used as a catalyst support, but is still poorly understood at the atomistic level due to limitations in both experimental and computational methods. We have developed and experimentally validated a method for generating realistic atomistic surface models of amorphous silica for a range of temperatures by simulating the process of surface dehydroxylation.

Using these surface models, we have studied the effects of amorphous silica supports on small platinum NPs (13 and 55 atoms) with regards to their catalytic properties. We find that the morphology of Pt clusters undergo significant restructuring that depends on the local structure at the Pt-Silica interface. This restructuring typically leads to significantly increased exposure of lower-coordination atoms than are present on the unsupported NP. In contrast, Pt55 typically undergoes only modest changes in lattice spacing and generally maintains its unsupported structure. The degree of restructuring as well as metal-support interaction strength is strongly correlated with the number of hydroxyl groups at the Pt-silica interface, and hence, the pretreatment temperature of the silica support. Preliminary investigations indicate that metal-support interactions can strongly affect the binding of CO and O for Pt13.

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