Date: March 29, 2016
A US Patent (US Patent No.: 9,283,545) entitled "Efficient and Recyclable Heterogeneous Nanocatalysts” was recently issued to Professor Tewodros (Teddy) Asefa and his former post-doctoral fellows, Dr. Ankush V. Biradar and Dr. Yanfei Wang. The invention in the patent is on novel design and synthetic methods to a series of easily separable and recyclable efficient nanocatalytic systems that can find a range of applications in industrially and commercially relevant chemical reactions and conversions of fine chemicals into value-added products.
The catalytic nanoparticles comprise silica nanoparticle cores covalently attached to dendrimers encompassing at least one type of catalytic species. The catalytic species may be a metal catalyst such as Pd nanoparticles. Methods of synthesizing these catalytic nanoparticles and their efficient and recyclable properties are provided. The Pd nanoparticles to exhibit high catalytic activities by the virtue of their ease of interaction with reactants, as demonstrated here with catalytic hydrogenation reactions. Thus, these materials can serve as easily recyclable and efficient catalysts that can be used in catalytic reactions (e.g., hydrogenation) of various substrates at room temperature and under moderate pressure.
In a related system, silica microsphere-supported Pd nanoparticles that are encapsulated with a hollow and nanoporous ZrO2 shell were fabricated as yolk-shell catalytic nanoreactors. The hollow and nanoporous ZrO2 shell of these microspheres, dubbed SiO2/Pd/h-ZrO2 microspheres, is permeable enough to allow reactants reach the Pd multicores, while at the same time let the Pd nanoparticles remain intact. The microspheres exhibit excellent catalytic activity and selectivity for the hydrogenation reaction, as shown with hydrogenation of two different olefins and a nitro functional group, at room temperature and under ambient H2 pressure. This effective catalytic activity even at room temperature and moderate pressure was the result of the assembly of SiO2-supported ~5 nm Pd nanoparticle multicores within a hollow and nanoporous ZrO2 shell. Furthermore, the structure enabled the Pd nanoparticles to remain stable without losing their catalytic activities, even after several cycles of catalytic reactions. The protection of the Pd nanoparticles from aggregation/sintering by the nanoporous, hollow ZrO2 shell is particularly interesting considering the fact that the Pd nanoparticles have ‘naked’ surfaces or no organic surface passivating ligands that are typically needed to stabilize metallic nanoparticles. This, in turn, allowed the Pd nanoparticles to exhibit high catalytic activities by the virtue of their ease of interaction with reactants, as demonstrated with catalytic hydrogenation reactions, and yet easily recyclable after the reactions.
|Dr. Tewodros Asefa
|Dr. Ankush V. Biradar
|Dr. Yanfei Wang