Well-dispersed gold nanoparticles (AuNPs) on a solid support with control of particle size is a goal for heterogeneous catalysis. Experiment has shown that the Zr-based metal-organic framework NU-1000 can be used as both a size-defining template and a support for the growth of AuNPs. These AuNPs have been shown to be catalytically competent for reduction reactions and could be effective for selective oxidative catalysis. A key step in gold-catalyzed oxidations is the activation of O2, which has not yet been studied within a MOF. In this work, the energies of isomeric Au13 and Au38 NPs confined in NU-1000 have been characterized computationally together with an examination of O2 activation thereupon. In particular, periodic density functional theory calculations were performed with the AuNPs incorporated into the triangular pores of NU-1000, and O2 binding was studied for the most stable conformations. We find that the well-studied Au38 cuboctahedron is not stable inside the triangular pore, but instead relaxes to more stable and less symmetric structures having 5- or 4-atom cores, which are similar to geometries found to be at low energy when in isolated form in a previous study. These NPs have singlet spin ground states. Within the triangular pore, O2 binding on exposed gold surfaces is sensitive to the gold surface arrangement and the overall spin. Tuning the gold surfaces through gold-linker interactions could be a one way to optimize the activity of gold catalysts within MOFs.

Gold nanoparticles in the NU-1000 metal organic framework: Structures and O2 activation

2019 Fall National Meeting

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