Latest Research Results

Research Finding #1

"Oriented Catalytic Platinum Nanoparticles on High Surface Area Strontium Titanate Nanocuboids"

James A. Enterkin*†§, Kenneth R. Poeppelmeier†§, and Laurence D. Marks‡§
† Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States
‡ Department of Materials Science and Engineering, Northwestern University
2220 Campus Drive, Evanston, Illinois 60208, United States
§ Institute for Catalysis in Energy Processes and Center for Catalysis and Surface Science
Northwestern University, 2137 Sheridan Road, Evanston, Illinois 60208, United States
Nano Letters (ACS Publications), February, 2011

Researchers at Northwestern University's Institute for Catalysis in Energy Processing have discovered a new strategy for fabricating metal nanoparticles in catalysts which promises to enhance the selectivity and yield for a wide range of structure-sensitive catalytic reactions. Because many industrial processes are dependent on catalysis, any advance in the design of catalysts can provide significant benefits to society.

Although catalytic supports are often selected for their high surface area or thermal, chemical, and mechanical stability, the support can also affect the selectivity and reactivity of the catalyst. (1-3) Classic catalytic work, for example that of Sinfelt and co-workers,(4-7) has shown that changing the support can dramatically alter the catalytic behavior.

Many theories have been proposed to explain the general role of supports, including sites at the metal−support interface,(8) particle size and surface-structure sensitivities,(9) ensemble-size sensitivity,(10) and strong metal−support interactions.(11, 12) The latter includes concepts such as intermetallic bond formation and charge transfer,(13, 14) diffusion of metal species between support and catalyst,(1, 15, 16) geometric decoration,(17-22) and other electronic effects.(23, 24) These insights have been gained from studies on model systems, largely single crystals. In the past, the various surface facets on high surface area supports have made these insights difficult to exploit, although the use of a support with both high surface area and controlled orientation may offer the opportunity to bridge this gap.



Platinum nanoparticles grown on SrTiO3 nanocuboids via
atomic layer deposition exhibit cube-on-cube epitaxy with
the predicted Winterbottom shape, consistent with literature
values of the interfacial and surface free energies. This
thermodyamically stable configuration should survive the
rigors of catalytic conditions to create stable, high surface area,
face-selective catalysts.
Research Finding #2

"A homologous series of structures on the surface of SrTiO3 (110)"
James A. Enterkin (first author), Arun K. Subramanian, Kenneth R. Poeppelmeier and Laurence D. Marks, NU
Bruce C. Russell and Martin R. Castell, Oxford University
Nature Materials

A collaboration between researchers at Northwestern University's Catalysis Center and scientists at Oxford University has produced a new approach for understanding surfaces, particularly metal oxide surfaces, widely used
in industry as supports for catalysts. This knowledge of the surface layer of atoms is critical to understanding a material's overall properties. The findings were published online Feb. 14 by the journal Nature Materials.

Enterkin et al, A homologous series of structures on the surface of SrTiO3 (110), Nature Materials doi:10.1038/nmat2636

Figure (right): Structure of the SrTiO3 (110) 3x1 surface, showing the yellow surface TiO4 tetrahedra as well as the titanium atoms (grey), oxygen (red) and strontium (green).

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Research Finding #3

“Development and application atomic-scale electron microscopy, spectroscopy and 3D tomography
for catalyst characterization”
J.S. Wu, S.Y. Li and V.P. Dravid

The ALD process is similar to chemical vapor deposition (CVD) but separates the two steps of loading and oxidizing the precursor. There is about 1 gram of zeolite (also at 100oC) which lies flat on a bed with a screen covering the zeolite to keep the zeolite from blowing about. The ferrocene is sublimed for ~6hours. Afterwards the sample is then calcined for 5 hours at 550 C to oxidize the precursor. From the tilted series, it is clear that most of the Fe nanoparticles are within the zeolite.

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Research Finding #4

"Controlled Growth on Platinum Nanoparticles on Strontium Titanate Nanocubes"
S. T. Christensen, J. W. Elam, Q. Ma, S. J. Weigand, B. Lee, S. Seifert, Argonne National Laboratory
F. A. Rabuffetti, P. C. Stair, K. R. Poeppelmeier, M. C. Hersam, and M. J. Bedzyk
Northwestern University

With an eye toward increasing the surface-to-volume ratio for heterogeneous catalysis, Pt nanoparticles are grown by atomic layer deposition (ALD) on the surfaces of SrTiO3 nanocubes. The SrTiO3 nanocubes are prepared by sol-precipitation-hydrothermal treatment and average 60 nm on a side, while the ALD-deposited Pt forms discrete and well-dispersed nanoparticles at the few-nanometer length scale. As the number of ALD cycles increase, X-ray absorption near edge structure (XANES) spectra show a progression from platinum (II) oxide to metallic platinum. The extended X-ray absorption fine structure (EXAFS) also indicates a decrease in Pt-O bonding and an increase in Pt-Pt bonding with increasing ALD cycles. This exquisite structural and chemical control demonstrates the utility of ALD for preparing nanostructured catalyst materials.

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