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The Cage Stage

Using 3-D silica nanocages to protect environmentally critical catalysts

Effective metal catalysts are vital to pollution prevention and clean energy production, and thus central to the interests of the Department of Energy and the nation. Preventing nanosized catalyst particle sintering has remained a great challenge within the field of catalysis research. Pacific Northwest National Laboratory researchers have intricately studied a new cubic mesostructured silica (SBA-16) catalyst support that uses its cage-like 3-D structure to protect metal and metal oxide nanoparticles, keeping them safe from heat damage. Using electron microscopy resources at DOE’s EMSL, the team of scientists not only demonstrated the effectiveness of SBA-16’s nanocages, but in the process also developed a class of SBA-16-supported, regenerable metal catalysts that remove unwanted sulfur from syngas fuel.

The PNNL team chose SBA-16 for its 3-D (cubic structured) advantages over other widely studied 2-D (hexagonal) supports. SBA-16 is resistant to pore- blocking, allows fast transport of reactants and products, and works well at raised temperatures—features which aid efficient, less costly catalysis in real- world applications. With synthesized SBA-16, the first step was to bait its empty cages by impregnation with metal precursors (nitrate salts). After calcination and reduction, high resolution transmission electron microscopy images taken at EMSL showed that the metal nanoparticles (nickel and copper) were firmly locked inside the SBA-16 cages—free to do their catalytic work (in this case adsorbing sulfur) without sintering and agglomerating from heat exposure. In a simulated biomass-derived syngas, the supported catalysts performed steadily through five desulfurization and regeneration cycles, showing greatly improved stability with the protection of SBA-16’s nanocages. Capitalizing on the unique structure of certain supports, this “confinement strategy” should be useful in preventing nanoparticle damage or migration in a variety of other applications.

Scientific impact: New insights into the formation and stability of metal particles confined within nanocages gives the catalysis research community promising direction for further research and development. This work supports EMSL’s goal of designing and synthesizing increasingly complex interfaces and surfaces.

Societal impact:
Optimizing efficient, regenerable catalysts leads to enhanced removal of pollutants at lower costs during chemical manufacturing, energy production, and automobile use—offering a future with cleaner air. Syngas in particular is produced in the gasification of biomass, and thus helps meet the demand for cleaner transportation fuels.

Reference: Liyu L, DL King, J Liu, Q Huo, K Zhu, C Wang, M Gerber, D Stevens, and Y Wang. 2009. “Stabilization of Metal Nanoparticles in Cubic Mesostructured Silica and Its Application in Regenerable Deep Desulfurization of Warm Syngas.” Chemistry of Materials 21(22):5358–5364. doi:10.1021/cm901227e.

Acknowledgment: This work was supported by PNNL’s Laboratory Directed Research and Development Program and DOE’s Biomass Energy Technology Program.

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Released: February 12, 2010