1. Water-Gas-Shift reaction over Pt/CeO 2 : spectators & reaction intermediates by an operando spectrokinetic analysis F.C. Meunier CenTACat, Queen’s University Belfast, UK Summer School in Energy and Environmental Catalysis University of Limerick, July 2005

2. Outline 1. Introduction - WGS Mechanisms over Pt/CeO 2 - SSITKA - DRIFTS cell design 2.Reactivity of surface species in 2  feeds R-WGS: 12 CO 2 /H 2 DRIFT: 13 CO 2 /H 2 (SSITKA) versus Ar purge 3. Spectators & Reaction intermediates R-WGS and WGS DRIFT + MS / SSITKA using a single reactor

3. The H 2 -economy

5. Today’s Typical PEM Fuel Cell Note: PEMFC proton-exchanged membrane fuel cell polymer electrolyte membrane fuel cell SPEFC solid polymer electrolyte fuel cell

6. 100-300 microns H2H2 O2O2 Today’s Typical PEM Fuel Cell

7. Steam reforming (SR) of Hydrocarbons Steam reforming of a hydrocarbon is essentially the reduction of water with this reductant to form a mixture of carbon oxides and hydrogen: a H 2 O + C x H y  b CO + c CO 2 + d H 2 The overall process requires 6 major steps:

8. Methane steam reforming equilibrium as a function of Temperature P = 1 bar H2O = 3 kmol CH4 = 1 kmol

9.  max yield of H 2 from CH 4 at high T  The proportion of CO/H 2 can be further modified by the water- gas-shift reaction CO + H 2 O  CO 2 + H 2  max yield of H 2 from CO at low T If only CO-free H 2 is required, need to use additional low T WGS reactors H2OH2O H2H2 CO 2 H2H2 CO WGS

10. Process diagram for H 2 production: reformer condition: PH 2 O/PCH 4 = 2.5-4.0, T exit = 900-1100, P exit = 20-30 atm

11. WGS Mechanisms over Ceria-based catalysts ATYPICAL FEED 2 H 2 CO O 2 H +  + The formate mechanism Shido, Iwasawa, J. Catal. 141 (1993) 71 Jacobs, Williams, Graham, Sparks, Davis, J. Phys. Chem. B 107 (2003) 10398 Jacobs, Davis, Appl. Catal B, 284 (2005) 31 OO HH Ce CO O C O H Ce O H O C OO H2OH2O OH H +H2+H2 CO 2 The Redox mechanism Bunluesin, Gorte, Graham, Appl. Catal. B, 15 (1998) 107 Li, Fu, Flytzani-Stephanopoulos, Appl. Catal. B, 27 (2000) 107 22322 H 2CeO OCe OH CO 2 (g) + Ce 2 O 3 2CeO 2 CO(ads) CO(g) + Pt + → + → + →

12. Outline 1. Introduction - WGS Mechanisms over Pt/CeO 2 - SSITKA - DRIFTS cell design 2.Reactivity of surface species in 2  feeds R-WGS: 12 CO 2 /H 2 DRIFT: 13 CO 2 /H 2 (SSITKA) versus Ar purge 3. Spectators & Reaction intermediates R-WGS and WGS DRIFT + MS / SSITKA using a single reactor

13. SSITKA: Steady-State Isotopic Transient Kinetic Analysis Combined IR (transmission) + MS / SSITKA Balakos, Chuang, Srinivas, J. Catal. 1993, 140, 281. For C isotopes: Conversion of syngas (CO / H 2 mixtures) CO 2 -reforming of methane Typically using either PFR or IR cell Combined DRIFTS + MS /SSITKA Single reactor

14. R R* Vent Tubular plug flow reactor Mass spectrometer R P R* P*P* SSITKA: Steady-State Isotopic Transient Kinetic Analysis time P

15. The “Classical” Analysis gives limited information   r = N Mean surface residence time (s) Rate of production (mol g -1 s -1 ) Concentration of active sites (mol g -1 ) Related to the “activity” of the sites Measured at steady state

16. Outline 1. Introduction - WGS Mechanisms over Pt/CeO 2 - SSITKA - DRIFTS cell design 2.Reactivity of surface species in 2  feeds R-WGS: 12 CO 2 /H 2 DRIFT: 13 CO 2 /H 2 (SSITKA) versus Ar purge 3. Spectators & Reaction intermediates R-WGS and WGS DRIFT + MS / SSITKA using a single reactor

17. Diffuse Reflectance Infrared Fourier Transform Spectroscopy What is it ? (DRIFTS) is a technique that collects and analyzes scattered IR energy. DRIFTS TRANSMISSION

18. R-WGS DRIFTS Setup O 2 H CO 2 H 2 +  + 2% Pt/CeO 2 (J.M.) Pre-reduced in 50% H 2 at 300°C T=225°C 1% 12 CO 2 + 4% H 2 Pre-reduced in 50% H 2 at 300°C T=225°C 1% 12 CO 2 + 4% H 2

19. Modified DRIFT cell: Residence Time Distribution Step Ar/Kr  Ar, 100 sccm total flow Kr normalised signal RTD /s

20. Non-modified DRIFT cell purge time ca. 300 s Flow rate: 150 sccm Jacobs and Davis, Appl. Catal. A 284 (2005) 31

21. Non-modified DRIFT cell purge time Formates Carbonyls Carbonates Dead zone? Jacobs and Davis, Appl. Catal. A 284 (2005) 31

22. Quantitative DRIFTS IoIo IoIo I Reflectance R oo = I / I 0 I Strongly absorbing matrix Olinger and Griffiths, Anal. Chem. 60 (1988) 2427, = “absorbance” Kubelka-Munk

23. Quantitative DRIFTS Wavenumber /cm 0.01.02.03 2200180014001000600 Detector signal /a.u. Matyshak and Krylov, Catal. Today, 25, 1 (1995) I o : incident beam I : over catalyst I ads : for feed + catalyst I I ads R oo = I / I 0 R = I ads / I 0 IoIo

24. Quantitative DRIFTS If I ~ Io Kubelka-Munk ‘Absorbance` Matyshak-Krylov

25. Outline 1. Introduction - WGS Mechanisms over Pt/CeO 2 - SSITKA - DRIFTS cell design 2.Reactivity of surface species in 2  feeds R-WGS: 12 CO 2 /H 2 DRIFT: 13 CO 2 /H 2 (SSITKA) versus Ar purge 3. Spectators & Reaction intermediates R-WGS and WGS DRIFT + MS / SSITKA using a single reactor

26. 2. Reactivity of surface species in different feeds ? Steady-state R-WGS feed ( 12 CO 2 +H 2 ) Pure Ar labelled R-WGS feed ( 13 CO 2 +H 2 ) Removal of 12 C-surface species Removal of 12 C-surface species

27. Assignment of the IR bands R-WGS: 1% 12 CO 2 + 4% H 2 T=225°C FORMATES 2941 2841 C H OO CARBONATES 866 851 C O OO 2059 C CARBONYLS O

28. Integration Method FORMATESCARBONATESCARBONYLS Formates: 2954-2944 cm -1, baseline at 3050 cm -1 ; Carbonyls: 2110-2050 cm -1, baseline at 2150 cm -1 ; Carbonates: 900-865 cm -1, baseline at 795 cm -1. Needs calibration, see P. Hollins

29. Validation of the integration method

30. Reactivity in Ar at 225°C Wavenumber (cm -1 ) FormatesCarbonatesCarbonyls 12 CO 2 +H 2 then Ar

31. Reactivity in Ar at 225°C Reactivity: Formates >> Carbonates Steady state 1% CO 2 + 4% H 2 Pure Ar

32. Reactivity during SSITKA at 225°C Wavenumber (cm -1 ) FormatesCarbonatesCarbonyls 12 CO 2 +H 2 then 13 CO 2 +H 2

33. Reactivity: Carbonates >> Formates Steady-state 1% 12 CO 2 + 4% H 2 Steady-state 1% 13 CO 2 + 4% H 2 Reactivity during SSITKA at 225°C

34. Conclusion DRIFT experiments Reactivity under Ar NOT representative of true reactivity of the surface species Tibiletti et al., Chem. Comm. (2004) 1636 Isotopic exchangeDesorption / Reaction in Ar O 2 H CO 2 H 2 +  +

35. Why does the feed composition matter? feed oxidising/reducing nature modify ceria surface oxidation state Meunier et al., Appl. Catal. A (2005) in press modify bonding strength of chemisorbed species

36. Outline 1. Introduction - WGS Mechanisms over Pt/CeO 2 - SSITKA - DRIFTS cell design 2.Reactivity of surface species in 2  feeds R-WGS: 12 CO 2 /H 2 DRIFT: 13 CO 2 /H 2 (SSITKA) versus Ar purge 3. Spectators & Reaction intermediates R-WGS and WGS DRIFT + MS / SSITKA using a single reactor

37. SSITKA (Single reactor) MS Determination of the Rate of RDS DRIFT Investigation Surface Species 3. Spectators & Reaction Intermediates ?

38. R-WGS: SSITKA / DRIFT + MS Setup Bruker FTIR Hiden MS PE 8700 GC DRIFTS cell MFC H 2 Ar 12 CO 2 V MFC H 2 Ar He H 2 Ar H 2 V 13 CO 2 MFC H 2 Ar 12 CO 2 V Vent MFC H 2 Ar H 2 H 2 V 13 CO 2

39. SSITKA / DRIFT+MS experiments 1% 12 CO 2 + 4% H 2 then 1% 13 CO 2 + 4% H 2 O 2 H CO 2 H 2 +  +

40. Formates Carbonyls Carbonates R-WGS: SSITKA / DRIFT+MS Results  = time for 50% exchange 55 ±6 secCarbonate 54 ±6 secCarbonyl 660 ±30 secFormate 57 ±2 sec 13 CO(g) O 2 H CO 2 H 2 +  +

41. Number of CO(g) precursors Area = f (CO precursors at the surface) 2.2 x 10 -4 mol g cat -1

42. 44 28 RWGS studied by TGA-MS at 225 °C 1% CO 2 + 4% H 2 in Ar Ar Moles of CO(g) (mol g cat -1 ) Formate conc. (mol g cat -1 ) 2.2 x 10 -4 < 1.4 x 10 -4 1h mm H2H2 Minority of “fast” formates cannot account for CO formation

43. Moles of CO(g) (mol g cat -1 ) CO(g) /Pt surface 2.2 x 10 -4 12 12-times more CO(g) precursors than surface Pt atoms CeO 2 CO Pt X Carbonyls cannot be the ONLY reaction intermediate Number of CO(g) precursors

44. Reaction Mechanism R-WGS (Minor route) (Main route) (Minor route) A. Goguet et al., J Phys. Chem. B 108 (2004) 20240

45. Experimental conditions WGS feed: 100 sccm of 1% 12 CO+ 10% H 2 O in Ar T=200°C O 2 H CO 2 H 2 +  + WGS: SSITKA / DRIFT+MS

46. WGS: SSITKA / DRIFT+MS Setup MFC 12 CO V MFC V CO MFC 12 CO V Vent Bruker FTIR Hiden MS Vent MFC Ar Kr Ar V PE 8700 GC 13 Water saturator DRIFTS cell Ar

47. Assignment of the IR bands RWGS 1% 12 CO 2 + 4% H 2 T=225°C 2941 2841 C H OO 866 851 C O OO 2059 C O 5001000150020002500300035004000 Wavenumber /cm -1 WGS 1% 12 CO+ 10 % H 2 O T=200°C Abs. (a.u.)

48. DRIFTS band evolution during 12 CO- 13 CO exchange during WGS

49. WGS: DRIFT + MS / SSITKA 12 C-Formates 13 CO 2 WGS: Formates also minor intermediate O 2 H CO 2 H 2 +  + CO(ads), carbonates ?

50. WGS: Comparison of IR and MS 13 CO 2 (g) signals during 12 CO- 13 CO switch MS not needed!

51. Conclusions Use steady-state or operando conditions to get true reactivity. SSITKA / (DRIFT + MS) using a single reactor CARBONATES: main reaction intermediate for R-WGS FORMATES: spectator /“minor” reaction intermediate for R-WGS & WGS Mechanistic studies: WGS – Pt/CeO 2

52. Outline 1. Introduction - WGS Mechanisms over Pt/CeO 2 - SSITKA - DRIFTS cell design 2.Reactivity of surface species in 2  feeds R-WGS: 12 CO 2 /H 2 DRIFT: 13 CO 2 /H 2 (SSITKA) versus Ar purge 3. Spectators & Reaction intermediates R-WGS and WGS DRIFT + MS / SSITKA using a single reactor

53. Acknowledgements Prof. Robbie Burch Prof. Chris Hardacre Dr John Breen Dr Daniele Tibiletti Dr Alex Goguet Dr Sergyi Shekhtman Mr David Reid

54. Acknowledgments