1. Catalysis and Catalysts - X-Ray Diffraction (XRD) X-Ray Diffraction Principle: interference of photons by reflection by ordered structures n = 2d sin  Interference positive for: Bragg’s law So, identification compound In real catalysts: line broadening the smaller the crystals the more line broadening So, from XRD crystallite diameter D can be estimated D = K / (b cos  ) b = peak width K = constant; usually ca. 1 d    d sin  2 

2. Catalysis and Catalysts - X-Ray Diffraction (XRD) Schematic of X-Ray Diffractometer Ionisation chamber rotates 2  degrees when the crystal rotates  XRD patterns: fingerprints of ordered solids XRD: unambiguous information on crystal structure  22 X-ray source Detector Crystal

3. Catalysis and Catalysts - X-Ray Diffraction (XRD) Active Phase of Industrial Catalysts is Microcrystalline KClNaClX-Ray Diffraction Data: a.b. 111 200 220 311 222 400 331 420 422 511 333 440 531 600 442 533 620 622 444 711 551 640 200 220 222 400 420 422 440 600 442 620 622 444 640 642 2  = 180 o 2  = 0 o Incident X-rays Diffraction line Undeviated X-rays Sample Photographic film

4. Catalysis and Catalysts - X-Ray Diffraction (XRD) X-Ray Diffraction Patterns WO 3 /SiO 2 WO 3 /Al 2 O 3 WO 3 (1.5 -100 wt%) WO 3 (0 -29 wt%) WO 3 /SiO 2 -W wt% WO 3 100 37 20 12 6 3 1.5 60 50 40 30 20 10 2  (degrees) WO 3 /Al 2 O 3 -D wt% WO 3 0 0.9 1.8 3.6 7.4 13 29 70 60 50 40 30 20 10 2  (degrees)

5. Catalysis and Catalysts - X-Ray Diffraction (XRD) Solid-State Diffusion of Co into Al 2 O 3 9.1 wt% CoO/Al 2 O 3 Calcination T: 1290 K 1025 875 675 380 * bulk CoAl 2 O 4 80 70 60 50 40 30 20 2  (degrees) o n m l k j i h g f e d c b a

6. Catalysis and Catalysts - X-Ray Diffraction (XRD) 2  -line position of “Al 2 O 3 and CoAl 2 O 4 ” diffraction line at about 80 degrees Above 900 K the intensity of spinel lines increases, Al 2 O 3 lines shift: Conclusion: above 800 K Co 2+ diffuses into the bulk Calcination temperature (K) 600 800 1000 1200 79.6 79.4 79.2 79.0 78.8 2  (degrees)

7. Catalysis and Catalysts - X-Ray Diffraction (XRD) Thermal Stability of NiO-WO 3 /Al 2 O 3  Does Ni 2+ diffuse into alumina?  If so, does WO 3 influence the rate of diffusion? T unit cell size 2d sin  = n

8. Catalysis and Catalysts - X-Ray Diffraction (XRD) Change of Unit Cell Size vs Calcination Temperature NiO(4.1)/Al 2 O 3 NiO(5.1)WO 3 /Al 2 O 3 calculated 675 875 1075 Calcination temperature (K) 791.0 792.7 794.4 796.0 797.7 a

9. Catalysis and Catalysts - X-Ray Diffraction (XRD) Calculated Concentration Profiles of Ni in Al 2 O 3 Crystallites Al 2 O 3 NiAl 2 O 4 t = 0 2.9  10 -9 m 2 /s 251 kJ/mol r (nm) C/CeC/Ce 0 1 2 3 4 5 6 543210543210 875 K 925 K 975 K 1025 K a b c d

10. Catalysis and Catalysts - X-Ray Diffraction (XRD) Summary of XRD  A “must” in catalyst characterisation  structure of crystalline phases (nm range)  Crystal dimension  Hydrotreatment: –diffusion of Ni and Co follows Fick’s law –Ni rate of diffusion not influenced by W oxide –Ni and Co diffusion during reaction negligible