1. Adsorption and Catalysis Dr. King Lun Yeung Department of Chemical Engineering Hong Kong University of Science and Technology CENG 511 Lecture 3

2. Physical Adsorption Texture and morphology –specific surface area of catalyst –pore size –pore shape –pore-size distribution (same size or various sizes?) –pore volume

3. Pore Size and Shape Pore Diameter –micropores (< 2 nm) –mesopores (2 – 50 nm) –macropores (> 50 nm) Pore Shape –cylinder –slit –ink-bottle –wedge

4. Pore Size and Shape Pore Structure Silica Carbon Zeolite

5. Pore Size and Shape Why is it important? it dictates the diffusion process through the material.

6. Pore Size and Shape Why is it important? directly affect the selectivity of the catalytic reaction.

7. Pore Size and Shape Measurement Techniques 1 10 100 1000 10000 Pore diameter (nm) Micro Meso Macro 2 50 N 2 capillary condensation Hgporosimetry

8. N 2 Physisorption Adsorption and Desorption Isotherms Adsorption Desorption

9. Adsorption and Desorption Isotherms III n ad p / p 0 VI n ad p / p 0 V n p / p 0 I n p / p 0 p / p II n ad 0 B IV n ad p / p 0 B N 2 Physisorption

10. Isotherms Assumptions: homogeneous surface (all adsorption sites energetically identical) monolayer adsorption (so no multilayer adsorption) no interaction between adsorbed molecules I n ad p / p 0 Type I Langmuir Adsorption Isotherm

11. Isotherms Multilayer adsorption (starting at B) Common for pore-free materials p / p n ad 0 B Type II Type IV Similar to II at low p Pore condensation at high p n ad p / p 0 B

12. Isotherms Type III Type IV n ad p / p 0 Strong cohesion force between adsorbed molecules, e.g. when water adsorbs on hydrophobic activated carbon n ad p / p 0 Similar to III at low p Pore condensation at high p

13. Physisorption Surface area measurement

14. Physisorption Different Adsorbates Used in Physisorption Studies

15. N 2 Physisorption Adsorption and Desorption Isotherms Langmuir Adsorption? No: strong adsorption at low p due to condensation in micropores at higher p saturation due to finite (micro)pore volume

16. BET Isotherm

18. Nonporous Silica and Alumina Low p/p 0 : filling of micropores favoured adsorption at most reactive sites (heterogeneity) High p/p 0 : capillary condensation Range 0.05 < p/p 0 < 0.3 is used to determine S BET BET equation

19. Pore Size and Surface Area

20. Pore Size Distribution Kelvin Equation

21. Pore Size Distribution Kelvin Equation Cylindrical pore Ink-bottle pore Pore with shape of interstice between close-packed particles Adsorbed layer t dpdp dmdm

22. Kelvin Equation

23. Pore filling Model Cylindrical Pore Channel

24. Hysteresis Loop Information on pore shape

25. Pore Size Distribution t-Method n ad t Proportional to S t Note: n ad is experimental result t is calculated from correlation t versus p

26. Kelvin Equation t-Method

27. Kelvin Equation Shape of t-plots

28. Kelvin Equation Interpretation of t-Plot  -alumina

29. Kelvin Equation Pore Size Distribution  -alumina r = t + 2  V RTIn P0P0 P

30. Mercury Porosimetry Pore Size Distribution

31. Mercury Porosimetry Pore Size Distribution  -alumina

32. N 2 Physisorption versus Hg Porosimetry Hg cannot penetrate small (micro)pores, N 2 can Uncertainty of contact angle and surface tension values Cracking or deforming of samples

33. Texture Data on Common Catalysts

34. N 2 Adsorption Isotherms & Pore Volume Distributions wide-pore silica  -alumina N 2 Adsorption Isotherms & Pore Volume Distributions

35.  -alumina activated carbon

36. Raney NiZSM-5 N 2 Adsorption Isotherms & Pore Volume Distributions

37. wide-pore silica  -alumina Hg Intrusion Curves & Pore Volume Distributions

38.  -alumina activated carbon

39. Raney NiZSM-5 Hg Intrusion Curves & Pore Volume Distributions

40. BET- & t-plots wide-pore silica  -alumina

41.  -alumina activated carbon BET- & t-plots

42. Raney NiZSM-5 BET- & t-plots

43. Chemisorption Surface Characterization Specific surface area of phases Types of active sites Number of active sites Reactivity of active sites Stability of active sites

44. Chemisorption Metal Dispersion

45. Adsorption Mode

46. Adsorption Stoichiometry

47. Particle Size and Dispersion

48. Supported Metal Particles

49. Number of Surface Atoms

50. Pulse Chemisorption

51. Monolayer capacity: 0.06 mmol / g Pt On-line Thermoconductivity Detector

52. Step Chemisorption On-line Mass Spectrometer

53. Temperature Programmed Desorption Adsorption Site Differentiation NH 3 desorption from HZSM-5

54. Temperature Programmed Desorption Adsorption Energetics After ammonia saturation the sample is degassed at 120 °C for 60 minutes Heating Rate of 5, 10, 15 and 20 °C/min

55. Temperature Programmed Desorption Adsorption Energetics Beta = heating rate [K / min] Tp = maximum desorption peak temperature Ed = Desorption energy [Kj / mole] A = Arrhenius factor R = 8.314451 [J / mol K] 12.49A factor 24.51Ed (kJ/mole) 5.4639Intercept 2948.07Slope

56. Temperature Programmed Reduction –characterisation of oxidic catalysts and other reducible catalysts –qualitative information on oxidation state –quantitative kinetic data –optimisation of catalyst pretreatment

57. Temperature Programmed Reduction Fe 2 O 3

58. Temperature Programmed Reduction Fe 2 O 3 Dry H 2 /Ar

59. Wet H 2 /Ar (3% H 2 O) Temperature Programmed Reduction Fe 2 O 3

60. Temperature Programmed Reduction Fe 2 O 3

61. Kinetic Models for Reduction

62. Infrared Spectroscopy

63. Reactor Cell DRIFTS Transmittance

64. Analysis of Catalyst Preparation Surface Hydroxyl Groups NH 4 ReO 4 Alumina Dry impregnation Drying 383 K, 16 h Calcination 323 K, 2 h Re 2 O 7 / Alumina

65. Analysis of Catalyst Preparation

66. IR Probe Molecule Acidity Measurement

67. IR Probe Molecule Acidity Measurement

68. Kelvin Equation Pore Size Distribution

69. Kelvin Equation Pore Size Distribution

70. In-Situ Reaction Study TCE Photocatalytic Oxidation

71. In-Situ Reaction Study PCO of Ethylene

72. In-Situ Reaction Study PCO of 1,1-DCE

73. In-Situ Reaction Study PCO of cis-1,2-DCE

74. In-Situ Reaction Study PCO of trans-1,2-DCE

75. In-Situ Reaction Study PCO of TCE

76. In-Situ Reaction Study PCO of Tetrachloroethylene