Exploiting X-ray diffraction techniques for catalytic materials characterization

por Brad Losey, Wednesday, 8th September 2021

Structural Analysis

Catalysts have become critical materials for a wide variety of applications in our modern-day industrial world. Among the different types of techniques we can utilize to characterize catalytic materials, X-ray diffraction (XRD) holds a unique place because we can utilize it to obtain both qualitative and quantitative phase information of crystalline materials as well as for the analysis of amorphous and nanomaterials. While heterogeneous catalysts are ideally suited for XRD analysis, one can also study both homogeneous and biocatalysts via this method.

In a recent white paper, Characterization of Catalytic Materials on Laboratory-Based X-Ray Diffraction Platforms, we highlight several techniques that you can perform on Malvern Panalytical’s floor-standing and compact XRD platforms to assist in the characterization of catalytic materials. Many may be familiar with X-ray powder diffraction (XRPD) for the analysis of crystalline materials (i.e. phase identification and quantification) through Bragg’s Law, as depicted in Figure 1. Malvern Panalytical’s line of XRD instruments can provide this information for both crystalline and amorphous phases as well as providing information about crystallite size and microstrain through the examination of the peak breadths.

Figure 1 Illustration of Bragg diffraction from a crystalline material. At a specific angle (θ) the two waves scattered from atoms separated by a distance (d) will interfere constructively and a signal will be detected, (n = 1,2, 3…).

In addition, specialized XRD methods such as non-ambient (NA) measurements along with X-ray scattering techniques such as pair distribution function analysis (PDF) and small-angle X-ray scattering (SAXS), can provide a more in-depth understanding of catalytic materials. One can examine catalytic samples under relevant non-ambient conditions to explore reaction pathways, observe phase changes, and examine the material’s thermal stability. Utilizing various non-ambient stages, available on both floor standing and compact models, you can precisely control the temperature, humidity, and atmosphere during measurements. Furthermore, one can obtain information about particle size and shape as well as short- and intermediate-range order through the aforementioned X-ray scattering techniques which have traditionally been relegated to synchrotron facilities. However, thanks to technologies such as our ScatterX78 stage and GaliPIX3D detector, these measurements can now be performed in-house [1,2].

Instrument Versatility

It is quite easy to perform standard powder XRD measurements, including those under non-ambient conditions (up to 500° C), on the Aeris compact X-ray diffractometer. This instrument has a comparable resolution, scan times, and peak intensities to the floor-standing Empyrean system. Furthermore, you can perform all of the standard XRPD measurements, as well as the aforementioned advanced techniques (NA, SAXS, and PDF), on a single Empyrean instrument with Malvern Panalytical’s PreFIX (Pre-aligned Fast Interchangeable X-ray modules) technology. This allows you to quickly exchange stages and optics without the need for re-alignment of the instrument. Figure 2 shows an example of a component mounted on the Empyrean instrument utilizing the PreFIX technology.

Figure 2 Image of an XRD accessory (beam knife) inserted in a PreFIX block on the Empyrean instrument.

Powerful Software

Our HighScore (Plus) software suite supports you with the analysis of data from both the Empyrean and Aeris platforms. With this package, phase identification and quantification can be easily performed along with more advanced analysis techniques such as the determination of lattice parameters, peak widths, crystallite size, micro-strain, and PDF analysis [3]. Furthermore, features like cluster analysis are also included in the HighScore Plus package and can be exploited for processing large datasets such as those obtained from non-ambient measurements [4]. Lastly, Malvern Panalytical’s EasySAXS software provides a straightforward method for obtaining relevant information from data collected during SAXS experiments. These include the volume-weighted size distribution, particle shape, and specific surface area [5]. Figure 3 shows examples of analysis performed in the two packages.

Figure 3 Analysis performed in the HighScore (Plus) software package: A.) Phase identification and quantification, B.) Cluster analysis, C.) PDF analysis. Additionally, an example of the EasySAXS user interface (D.) is shown.

True power comes from combining data

No doubt, XRD techniques can provide a more in-depth understanding of catalytic materials. in our white paper we highlight several techniques that you can perform on Malvern Panalytical’s floor standing and benchtop XRD platforms to assist in their characterization. Multiple techniques within the realm of XRD provide detailed information on a range of material properties and uncover key information.

I will explain the different characterization techniques and highlight their proven ability to support development and mass production during a webinar on September 28th. During this webinar I will discuss the following methods with an emphasis on their application to catalytic materials:

  • X-ray powder diffraction (XRPD)
  • Non-ambient X-ray diffraction
  • Line profile analysis (LPA)
  • Small-angle X-ray scattering (SAXS)
  • Pair distribution function (PDF) analysis.

References

  1. Te Nijenhuis, J., Gateshki, M., & Fransen, M. J. (2009). Possibilities and limitations of x-ray diffraction using high-energy x-rays on a laboratory system. Zeitschrift Für Kristallographie Supplements, 2009(30), 163-169. doi:10.1524/zksu.2009.0023
  2. Confalonieri, G., Dapiaggi, M., Sommariva, M., Gateshki, M., Fitch, A. N., & Bernasconi, A. (2015). Comparison of total scattering data from various sources: The case of a nanometric spinel. Powder Diffraction, 30(S1), S65. doi:10.1017/s0885715614001389
  3. Degen, T., Sadki, M., Bron, E., König, U., & Nénert, G. (2014). The HighScore suite. Powder Diffraction, 29(S2). , S13-S18. doi:10.1017/s0885715614000840
  4. Automatic analysis of large amounts of X-ray diffraction data with HighScore Plus. Malvern Panalytical application data sheet.
  5. Bolze, J.; Kogan, V.; Beckers, D.; Fransen, M. High-performance small- and wide-angle X-ray scattering (SAXS/WAXS) experiments on a multi-functional laboratory goniometer platform with easily exchangeable X-ray modules. Review of Scientific Instruments, 2018, 89(8), 085115.Bolze, J., Kogan, V., Beckers, D., & Fransen, M. (2018). High-performance small- and wide-angle X-ray Scattering (SAXS/WAXS) experiments on a MULTI-FUNCTIONAL laboratory Goniometer platform with easily EXCHANGEABLE x-ray modules. Review of Scientific Instruments, 89(8), 085115. doi:10.1063/1.5041949

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