XAFS and XRD techniques give complementary information about the structure of catalytic materials: XRD is effective in pure or mixed crystalline materials while XAFS provides short range order structural features in less ordered or amorphous materials. In addition, XAFS also gives information about the electronic properties of the catalysts. These two methods have been developed and advanced independently from each other at synchrotron sources in the US and abroad. To analyze catalysts under their operating conditions, this approach is often needed, namely, the simultaneous collection of the XRD and XAFS data under in situ conditions together with online product analysis.

The QAS team has built and tested the instrument for combined time-resolved XRD/XAFS experiments at beamline QAS. Such a combination allows the measurement of changes in the actual structure (in the short, medium and long range order), electronic properties and chemical activity of heterogeneous catalysts simultaneously. This is coupled with online gas analysis, dedicated for studying in situ chemical transformations.

The following references describe the development and application of combined XAFS-XRD capabilities at the SCC:

1) A. I. Frenkel, Q. Wang, N. Marinkovic, J. G. Chen, L. Barrio, R. Si, A. Lopez Camara, A. M. Estrella, J. A. Rodriguez, J. C. Hanson
Combining x-ray absorption and x-ray diffraction techniques for in situ studies of chemical transformations in heterogeneous catalysis: advantages and limitations
J. Phys. Chem. C 115, 17884-17890 (2011)

2) S. N. Ehrlich, J. C. Hanson, A. L. Camara, L. Barrio, M. Estrella,
C. Zhou, R. Si, S. Khalid, Q. Wang,
Combined XRD and XAS
Nucl. Instrum Methods Phys. Res. A 2011, 649, 213–215.