Beamline practice at BL14B2 (XAFS)
ver. 2011/9/13

T. Honma (JASRI)

1. Introduction
The bending magnet beamline, BL14B2, is used for various applications of XAFS over a wide
energy range from 3.8 to 72 keV. In the practical training course, we plan to show how to measure
XAFS spectra, which covers alignment of X-ray optics and sample position. We will also
demonstrate in-situ time-resolved quick scanning XAFS measurement of catalyst samples underreaction condition.

2. Plan of practice
9:30-

Introduction of XAFS analyses

10:30-

Preparation of tablet-form specimen.

11:30-

Introduction of beamline and alignment of the x-ray optics.

12:30-------- Lunch -----------

13:30-XAFS measurements of standard samples.

14:00-

Introduction of preliminary process of XAFS spectra using software ATHENA.

14:30-

Introduction of in-situ XAFS experiment

15:00-

Measurement of in-situ XAFS spectra of catalysts during reduction process.
During the measurement, data treatment and preliminary analysis of XAFS spectra.

17:00

Close.

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3. Alignment of x-ray optics and experimental stagez Figure 1 shows schematic layout of BL14B2.
z Main operation in alignment of x-ray optics is follows.
¾ Switch of diffraction plane of monochromator crystals between Si(111) and Si(311) tocover energy range for XAFS measurements.
¾ Change of glancing angle of mirror to remove higher-harmonic x-rays.
z Above operation slightly changes beam height downstream of monochromator.
z Fine adjustment of slits and mirrors in the optics and experimental hutches is done bymeasuring x-ray intensity using 1st ionization chamber in the experimental hutch (Fig. 2).
z The height of experimental stage in the experimental hutch is adjusted to x-ray beam byscanning in vertical direction.
z Fixed beam condition is achieved by adjusting the rotation angle of 1st crystal of
monochromator around beam axis to 2nd crystal.
z The control program for operation of x-ray optics realizes following x-ray beam.
¾ Quite low contamination (<10-4) of higher harmonics.
¾ Fixed beam position during XAFS scans passing through the center of slits in theexperimental hutch.
¾ Focused beam in vertical direction (0.2-0.5 mm).

Monochromator

Experimental hutch

MirrorSlit

Ionization chambers

X-ray
Slit
MirrorSlit
Optics hutch
Fig.1 Schematic layout of BL14B22Sample

4. Quick XAFS measurement in transmission modez Quick XAFS measurement is realized by data storage of x-ray detector output signals andBragg angles of monochromator in each memory board during continuous scanning.
z The arrangement and control system for transmission mode Quick XAFS measurements areshown in Figs. 2 and 3.
z Setup of measurement system¾ Set the beam size incident on the sample by slit opening.
¾ Set the gain of current amplifiers (Amp) for each ionization chamber.
z Operation of program of Quick XAFS measurement¾ Set the following parameters in the operation program
Energy range and step for a XAFS spectrum

Dwell time for a XAFS spectrum.

I0 ionizationchamber
X-ray

SampleFig. 2 Setup of transmission mode XAFS

3I ionizationchamberFig. 3 Control system of QXAFS measurement system in transmission mode

5. Preliminary process of XAFS spectra using software ATHENAz The row data of Quick XAFS spectra are processed to the ATHENA-readable data format.
z ATHENA processes the measured XAFS spectra, such as background removal and Fouriertransforms.
¾ ATHENA is one of most popular free software for processing XAFS data.
http://cars9.uchicago.edu/~ravel/software/¾ Model fitting of XAFS data is done by another software ARTEMIS including interfaces toATOMS and FEFF.

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6． Measurement of in-situ XAFS spectra in transmission mode
6.1 Sample preparationz The sample for XAFS measurement is form into thin disks of 7 mm diameter by pressmachine with very weak pressing force.
z Put adequate number of disk samples (around 20) into sample holder to achieve edge jumpabsorbance around 1.

Fig. 4 Mount of disk sample into inner holder of sample cell5

6.2 Setup of in-situ XAFS equipmentsz Experimental condition in this in-situ measurement¾ Sample: Pd/USY catalyst¾ Measurement energy: around Pd K-edge (24.3 keV)
¾ Sample temperature: room temperature¾ Reaction gases: H2, He and their mixture
z Set the sample cell including disk samples.
z Connect Q-mass to outlet of sample cell to monitor the concentration of each outlet gas.

GasSample cellFig. 5 Setup of in-situ XAFS equipments

66.3 In-stu XAFS measurement of catalyst during reduction processz XAFS measurement of catalyst in initial state.
¾ Flow 100%-He 100 ccm into sample cell.
¾ Measure Quick XAFS spectra in transmission mode.
¾ The measurement time of each XAFS spectra during this experiment is about 30 s.
z XAFS measurement of sample during reduction process.
¾ Flow 8%-H2/He 100 ccm into sample cell for 15-20 min.
¾ Measure Quick XAFS spectra every 30 s during gas flow.
¾ Check change of Fourier transform-XAFS spectra during reduction process usingATHENA.
¾ Stop 8%-H2/He flow.
¾ Flow 100%-He for 15-20 min until no residual H2 in sample cell (checking by Q-mass).
¾ Measure Quick XAFS spectra.
¾ Check the sample color.

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