Investigation of the structure of platinum clusters supported in zeolite beta using the pair distribution function

Structural characterization of supported metal catalysts is a challenge because the metal clusters are small, usually polydisperse, and present in low loadings. Here, we describe the use of the pair distribution function (PDF) method to study the structure of platinum clusters supported in zeolite beta at a loading of 1.1% w/w. In addition to the characterization by the PDF method, the sample was characterized using X-ray diffraction, X-ray photoelectron spectroscopy, X-ray absorption, and dark-field scanning transmission electron microscopy. With these techniques, we were able to determine that the platinum clusters were in a reduced state, monodisperse, and located mainly in the pores. With the PDF technique, we were able to determine that the local structure of the clusters was similar to that of the bulk platinum. Contrary to what might be expected, the PDF results showed that the lattice parameters did not change significantly. However, attempts to model the PDF using a finite cluster with the bulk platinum structure did not yield quantitative agreement to experiment, and it was determined that there were other interactions besides that of Pt-Pt affecting the PDF. Models that take into consideration different possible cluster shapes and sizes are necessary to completely describe the PDF at these low loadings. However, the PDF technique was shown to be valuable for the experimental determination of the structure of supported nanoclusters.