Catalytically Active Silicon Oxide Nanoclusters Stabilized in a Metal–Organic Framework

Post-synthetic modification of the zirconium-based metal–organic framework (MOF) NU-1000 by atomic layer deposition (ALD), using tetramethoxysilane (Si(OMe)₄) as a precursor, led to the incorporation and stabilization of silicon oxide clusters composed of only a few silicon atoms in the framework's pores. The resulting SiO_x functionalized material (Si-NU-1000) was found to be catalytically active despite the inactivity of related bulk silicon dioxide (SiO₂), thus demonstrating the positive effects of having nanosized clusters of SiO_x. Moreover, Si-NU-1000 showed activity greater than that found for aluminum oxide based catalysts—oxides known for their high acidity—such as an aluminum oxide functionalized MOF (Al-NU-1000) and bulk γ-Al₂O₃. X-ray photoelectron spectroscopy and infrared spectroscopy measurements unmasked the electron donating nature of Si-NU-1000, explaining the unusual electronic properties of the nanosized SiO_x clusters and supporting their high catalytic activity.