(269f) Evaluation of in-Situ Synchrotron Techniques for Dynamic Structural Analysis of Supported Bimetallic Nanoparticles

Oxford, S. M., Northwestern University
Chupas, P. J., Argonne National Laboratory
Chapman, K. W., Argonne National Laboratory
Lee, P. L., Argonne National Laboratory
Kung, M. C., Northwestern University

Supported bimetallic catalysts are of great interest due to the potential for favorable synergy between the metals resulting in catalysts that are superior to single metals. Combinations of Group 10 and Group 11 such as PtCu have been investigated for a variety of industrial applications including dechlorination, dehydrogenation, nitrate reduction, or PROX reaction. With all supported bimetallic catalysts, detailed and accurate characterization of the structure of the nanoparticles is challenging; this is particularly true for in-situ response to various gas atmospheres or under reaction conditions. Yet, the ability to gather this information is crucial to the development of improved bimetallic catalysts.

In this work we studied Al2O3 supported PtCu bimetallic nanoparticles in an effort to develop reliable methods of characterizing the distribution of metals in supported bimetallic nanoparticles. Using a combination of Transmission Electron Microscopy, Fourier Transform Infrared Spectroscopy (FTIR), X-ray Absorption Spectroscopy, and analysis of the Pair Distribution Function we analyzed the particle size distribution, the amount of CO adsorbed and the frequency of its vibrations, and the coordination numbers of the three metal-metal bond types. Specifically, we tracked the changes in these parameters resulting from long term treatments in a strongly adsorbing gas, CO. This treatment served as a model for future experiments using true reaction conditions.

Using FTIR as a benchmark, we confirmed that the x-ray techniques are indeed able to track very small structural changes (<10% change in coordination numbers) in-situ. While there is some degree of uncertainty, this work is the first example of this type of analysis and is promising for future development. A key feature of the results is that the techniques used are applicable to true reaction conditions, whereas conventionally, the most powerful methods of structural analysis are only applicable in vacuum conditions.

Use of the Advanced Photon Source at Argonne National Laboratory was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. The authors thank the staff at beamlines 11-ID-B and 5-BM-D for their help.