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Uniform nano-clusters signal improved catalysts



A scanning tunneling microscope image (left) shows nano-clusters deposited on a titanium dioxide platform with consistent orientation of the atoms (right). The dark triangle indicates the center of the tungsten trioxide molecular ring on the platform; the brighter side depicts the raised atom.

A new model system of nanostructures has been synthesized and could lead to control of chemical transformations critical for enhancing the nation's energy future.

This new nanostructure model system, developed by researchers at the Pacific Northwest National Laboratory, the University of Texas-Austin (UT) and Washington State University, offers insights into the structure and reaction mechanism of metal oxides. Metal oxides are important catalysts for producing fuels for transportation and value-added chemicals.

In the new model system, nanoclusters composed of cyclic tungsten trioxide line up molecule-by-molecule on a titanium dioxide platform. One tungsten atom from each cluster is raised slightly, holding forth the potential to execute catalytic reactions--a striking difference from commercial catalysts. Commercial catalysts vary in size and chemical composition, making it difficult to understand or predict the reactions taking place at the molecular level. In the new model, all the nanoclusters are the same size, evenly dispersed, and oriented in one of two directions on the titanium oxide crystal layer.

This unique, uniform feature may enable scientists to predict with increased accuracy and control the reactions that will occur, thereby enhancing the effectiveness of catalytic reactions. The researchers employed specialized equipment at the Environmental Molecular Sciences Laboratory, a DOE user facility on the PNNL campus, to prepare and characterize the platform as well as the clusters.

Using a unique approach that changed the tungsten oxide directly from a solid to a gas, the researchers successfully stabilized the molecular rings--or "trimers"--of tungsten on the titanium platform. The new nanostructure model system was developed as part of the Early Transition Metals as Catalysts project at PNNL, supported by the DOE Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division.

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