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-Al₂ O₃ . 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.