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 

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

Catalysis and Catalysts - X-Ray Diffraction (XRD) Active Phase of Industrial Catalysts is Microcrystalline KClNaClX-Ray Diffraction Data: a.b  = 180 o 2  = 0 o Incident X-rays Diffraction line Undeviated X-rays Sample Photographic film

Catalysis and Catalysts - X-Ray Diffraction (XRD) X-Ray Diffraction Patterns WO 3 /SiO 2 WO 3 /Al 2 O 3 WO 3 ( wt%) WO 3 (0 -29 wt%) WO 3 /SiO 2 -W wt% WO  (degrees) WO 3 /Al 2 O 3 -D wt% WO  (degrees)

Catalysis and Catalysts - X-Ray Diffraction (XRD) Solid-State Diffusion of Co into Al 2 O wt% CoO/Al 2 O 3 Calcination T: 1290 K * bulk CoAl 2 O  (degrees) o n m l k j i h g f e d c b a

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)  (degrees)

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

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 Calcination temperature (K) a

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 =  m 2 /s 251 kJ/mol r (nm) C/CeC/Ce K 925 K 975 K 1025 K a b c d

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