Using XRD to Determine Crystallite Size in Pt/C Catalysts

Approximately 90 vol% of the production of chemicals worldwide is related to heterogeneous catalysis. Heterogeneous catalysis is vital for the reduction of the energy needed for this process, and to guide a chemical reaction to the desired product.

Using XRD to Determine Crystallite Size in Pt/C Catalysts

The most important part of heterogeneous catalysis is the active surface of the catalyst, which achieves the best efficiency, and because of this, activated base materials, typically usually carbon or ceramics with large surface area, are infused with the active compound: nanoparticles of metals.

Measuring the size of the nanoparticles, especially after the materials have been recycled, is one method of gauging the quality of the catalyst. The most widely used method to define nanoparticles’ crystallite size is by using X-ray diffraction (XRD). With XRD, the peak width of reflections is in direct correlation to the size of the scattering domain through Scherrer’s equation. As a result, it is possible to conclude the crystallite size (CS) by determining the width of reflection in the diffraction pattern.

Using XRD to Determine Crystallite Size in Pt/C Catalysts

About the Thermo Scientific™ ARL™ EQUINOX 100 X-Ray Diffractometer

The Thermo Scientific™ ARL™ EQUINOX 100 X-ray Diffractometer utilizes a custom-designed Cu (50 W) micro-focus tube with mirror optics for high flux, meaning no external water chiller is needed.

The ARL EQUINOX 100 Diffractometer is also able to offer rapid data collection times due to its unique curved position sensitive detector (CPS), which simultaneously measures all diffraction peaks. As a result, the ARL EQUINOX 100 Diffractometer is perfect for measuring reflection and transmission.

Case Study

For XRD measurements, Pt/C powder was measured 5 min in reflection with a zero background sample cup. To determine the crystallite size using the Williamson-Hall method, MDI JADE 2010 was used.

Results

A Le Bail fit was used in order to determine the FWHM of the reflections, and after this step, CS, with the Williamson-Hall method, (cf. Figure 1) was calculated. Strain and instrument broadening, which was defined from NIST660 LaB6, was also taken into account. Refinements provided a CS of 2.5 nm. This result is in strong accordance with values seen in the literature.

Diffraction pattern of Pt/C (green: Pt; blue: C); Williamson-Hall plot of Pt/C (Red area indicates 1.5 s).

Figure 1. Diffraction pattern of Pt/C (green: Pt; blue: C); Williamson-Hall plot of Pt/C (Red area indicates 1.5 σ).

Summary

The benchtop ARL EQUINOX 100 X-ray Diffractometer, used in conjunction with the MDI JADE 2010 Software suite, proves to be a convenient solution for those wishing to quickly and easily determine CS of Pt nanoparticles in Pt/C catalysts.

Acknowledgments

Produced from materials originally authored by Dr. Simon Welzmiller from Thermo Fisher Scientific.

This information has been sourced, reviewed and adapted from materials provided by Thermo Fisher Scientific - Elemental Analyzers and Phase Analyzers.

For more information on this source, please visit Thermo Fisher Scientific - Elemental Analyzers and Phase Analyzers.

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