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ELECTROCHEMICAL PROMOTION OF CATALYSIS

RSE-SEE Second Regional Symposium on Electrochemistry: June 6 to 10, 2010 , Sava Center, Belgrade, Serbia. ELECTROCHEMICAL PROMOTION OF CATALYSIS. Costas G. Vayenas Department of Chemical Engineering, University of Patras Patras GR-26500, Greece. ELECTROCHEMICAL PROMOTION (EP).

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ELECTROCHEMICAL PROMOTION OF CATALYSIS

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  1. RSE-SEE Second Regional Symposium on Electrochemistry: June 6 to 10, 2010 , Sava Center, Belgrade, Serbia ELECTROCHEMICAL PROMOTION OF CATALYSIS Costas G. Vayenas Department of Chemical Engineering, University of Patras Patras GR-26500, Greece

  2. ELECTROCHEMICAL PROMOTION (EP)

  3. PROMOTER CATALYST U O2- SUBSTRATE SUPPORTED CATALYSTS

  4. Metal-support interactions in Catalysis Toluene oxidation on Pt(0.5 wt.%)/MxOy • The support has a dramatic effect on catalyst performance. • Supports with high ionic mobility are usually the best. Saleh M. Saqer, D. I. Kondarides, X.E. Verykios, Topics in Catalysis 52 (2009) 517.

  5. Solid electrolytes in Catalysis : Measurement of oxygen activity or chemical potential on working catalysts 4FUo = mO2,catalyst – mO2, reference or 2FUo = RTln(aO,catalyst/0.211/2) Solid Electrolyte Potentiometry General conclusion: μO2,catalyst ≤ μO2,gas or aO,catalyst ≤ pO21/2 C. Wagner, Adv. Catal. 21 (1970) 323 C.G.V. and Saltsburg, J. Catal. 57 (1979) 296

  6. Can we influence electrochemically the surface oxygen activity ? Electrode configuration for electrochemical studies in catalysis using (a) the fuel cell type reactor and (b) the single-chamber type reactor

  7. Possible pathways of O(a) and Na(a) adsorbed species created at the three-phase boundaries via application of electric current • Desorption • Electrocatalytic Reaction • Spillover

  8. ELECTROCHEMICAL PROMOTION WITH O2- CONDUCTORS (a) (b) L=Dr/(I/2F) ; r=r/r0 In this experiment L =74000 ; r=26 S. Bebelis and C.G. Vayenas, J. Catalysis, 118, 125-146 (1989).

  9. CO oxidation on Pt/YSZ M. N. Tsampas, F.M. Sapountzi & C.G. Vayenas, Catalysis Today, 146, 351 (2009).

  10. CO oxidation on Pt/YSZ M. N. Tsampas, F.M. Sapountzi & C.G. Vayenas, Catalysis Today, 146, 351 (2009).

  11. Electrocatalysis: ln (I/I0)=αaFη/RT Electrochemical Promotion: ln (r/r0)=αNF(η-η*)/RT M. N. Tsampas, F.M. Sapountzi & C.G. Vayenas, Catalysis Today, 146, 351 (2009).

  12. CO oxidation on Pt/YSZ M. N. Tsampas, F.M. Sapountzi & C.G. Vayenas, Catalysis Today, 146, 351 (2009).

  13. ELECTROCHEMICAL PROMOTION (EP) Basic definitions: Rate enhancement ratio: ρ = r/ro Faradaic efficiency: Λ = (r-ro)/(I/nF) Λ ≈ 2Fro/I0 Promotional index: Pij = ((r-ro)/ro)/θj Basic equations: Correlation of the changes of catalystpotential with the changes of catalyst work function: eΔUWR = ΔΦ Effect of the work function variation on the catalytic rates: ln(r/ro)= α(Φ-Φ*)/kbT

  14. PERMANENT NEMCA D. Tsiplakides, J. Nicole, C.G. Vayenas, and C. Comninellis, J. Electrochem. Soc. 145(3), 905-908 (1998)

  15. ELECTROCHEMICAL PROMOTION WITH Na+ CONDUCTORS (a) (b) UWR , DF / eV C.G. Vayenas, S. Bebelis and S. Despotopoulou J. Catalysis, 129, 67-87 (1991). I.V. Yentekakis, G. Moggridge, R.M. Lambert and C.G. Vayenas, J. Catalysis, 146, 292-305 (1994).

  16. Effect of catalyst potential and sodium coverage on N2 selectivity F. Dorado, A. de Lucas-Consuegra, C. Jiménez, J.-L. Valverde, Appl. Catalysis A: General, 321 (2007) 86-92

  17. ELECTROCHEMICAL PROMOTION WITH PROTON CONDUCTORS (a) (b) M. Makri, A. Buekenhoudt, J. Luyten and C.G. Vayenas, Ionics, 2, 282-288 (1996)

  18. 1-BUTENE ISOMERIZATION ON Pd/NAFION L. Ploense, M. Salazar, B. Gurau, and E. S. Smotkin, JACS, 119, (47), pp 11550 - 11551

  19. ELECTROCHEMICAL PROMOTION IN AQUEOUS SOLUTIONS S. Neophytides, D. Tsiplakides, M. Jaksic, P. Stonehart and C.G. Vayenas, Nature, 370, 45-47 (1994)

  20. Common features of Heterogeneous Catalysis, Fuel Cell operation, Electrolysis and Electrochemical Promotion: 1. Solid state catalyst, 2. Adsorption, 3. ΔG < 0, 4. Yield control via DC current or voltage application (Adapted from N. A. Anastasijevic).

  21. (a) (b) (c) Sacrificial promoter mechanism The Faradaic efficiency  equals the ratio of the lifetimes of the strongly bonded promoting species and of the weakly bonded reactive oxygen ORIGIN OF EPOC WITH O2- CONDUCTORS S.G. Neophytides and C.G. Vayenas, J. Phys. Chem. 99, 17063-17067 (1995)

  22. Isotope oxygen 18O2 adsorption on Pt/YSZ (high Tads) Closed circuit gas adsorption (EPOC Conditions) Tads=275°C, 2 kL + 15 mA for 210 s b=0.5°C/s b3 • Strongly bonded oxygen (state b3) is indeed lattice oxygen • Weakly bonded oxygen (state b2) is indeed gas supplied oxygen • Although isotope scrambling is taking place, the two oxygen adsorption states retain their identity over many minutes b2 A. Katsaounis, Z. Nikopoulou, X.E. Verykios and C.G. Vayenas, J. Catalysis 222(1), 192-206 (2004). 11

  23. In situ TPD X. Li, F. Gaillard, P. Vernoux, Topics in Catalysis 2007, 44/3, 391

  24. XPS UWR=0 UWR=+1 V S. Ladas, S. Kennou, S. Bebelis, and C.G. Vayenas, J. Phys. Chem. 97, 8845-8847 (1993).

  25. XPS S. Ladas, S. Kennou, S. Bebelis, and C.G. Vayenas, J. Phys. Chem. 97, 8845-8847 (1993)

  26. XPS W. Zipprich, H.-D. Wiemhöfer, U. Vöhrer, and W. Göpel, Ber. Buns. Phys. Chem. 99, 1406-1413 (1995)

  27. PEEM B. Luerssen et al., Angew. Chem. Int. Ed. 45, 1-4 (2006)

  28. STM OBSERVATION OF THE ORIGIN OF EPOC WITH Na+ CONDUCTORS (a) (c) (b) M. Makri, S. Bebelis, C.G. Vayenas, K. Besocke & C. Cavalca, Surf. Science 369, 351-359 (1996).

  29. STM OBSERVATION OF THE ORIGIN OF EPOC WITH O2- CONDUCTORS; UWR = 1 V D. Archonta, A. Frantzis, D. Tsiplakides, C.G. Vayenas, Solid State Ionics 177, 2397-2401 (2006).

  30. TEMPERATURE PROGRAMMED DESORPTION (TPD) Mass Spectrometer Mass Spectrometer InletValve InletValve Pump Pump A. Katsaounis, Z. Nikopoulou, X.E. Verykios and C.G. Vayenas, J. Catalysis 222(1), 192-206 (2004).

  31. A. Katsaounis, Z. Nikopoulou, X.E. Verykios, C.G. Vayenas, J. Catal. 2004, 222, 192 ; 226, 197

  32. EPOC AND METAL-SUPPORT INTERACTIONS Rh/YSZ Rh/TiO2 Rh/TiO2(WO3) Rh/γ-Al2O3 Rh/SiO2 J. Nicole, D. Tsiplakides, C. Pliangos, X.E. Verykios, Ch. Comninellis, C.G. Vayenas, J. Catal. 204(2001) 23.

  33. COMPARISON OF EPOC OF Rh FILMS DEPOSITED ON YSZ AND METAL-SUPPORT INTERACTIONS OF Rh CATALYSTS DISPERSED ON VARIOUS SUPPORTS METAL-SUPPORT INTERACTIONS: Rate increases upon varying supports of increasing Φ NEMCA EFFECT (EPOC): Rate increases upon positive polarization, i.e. upon increasing Φ

  34. MECHANISTIC EQUIVALENCE OF EPOC AND METAL–SUPPORT INTERACTIONS Electrically controlled metal-support interaction “Wireless” self-driven NEMCA (EPOC) microsystem CATALYSIS IN PRESENCE OF A (CONTROLLABLE) DOUBLE LAYER

  35. Potential-Work function equivalence C. G. Vayenas, S. Bebelis, S. Ladas, Nature 343 (1990) 625.

  36. WORK FUNCTION-POTENTIAL EQUIVALENCE In general: eΔU=ΔΦ+eΔΨ Since eΔU=ΔΦ it follows: ΔΨ=0 Thus from Gauss’ Law Ψ=0, Thus a neutral double layer is present at the metal-gas interface

  37. EFFECTIVE DOUBLE LAYER AT METAL/GAS INTERFACE

  38. WORK FUNCTION EFFECT ON ENERGY OF ADSORPTION OF O2

  39. EFFECT OF ALKALI-INDUCED WORK FUNCTION CHANGE ON CHEMISORPTIVE BOND STRENGTH OF CO

  40. Cu34 cluster used to model the Cu(100) surface. Oxygen has been adsorbed on the central 4-fold hollow site. • Pt25 cluster used to model the Pt(111) surface. Oxygen has been adsorbed on the central 3-fold hollow site. The position of the adsorbed ions (or point charges) is also shown. G. Pacchioni, F. Illas, S. Neophytides, and C.G. Vayenas, Quantum-Chemical Study of Electrochemical Promotion in Catalysis, J. Phys. Chem. 100, 16653-16661 (1996). G. Pacchioni, J.R. Lomas, and F. Illas, Electric field effects in heterogeneous catalysis, Molecular Catalysis A: Chemical 119, 263-273 (1997).

  41. (a) (b) (a) Dependence of the position of the HOMO in Pt25 and of the Pt25/O adsorption energy, Eads, at the Stark and full self-consistent field (SCF) levels, as a function of the presence of point charge q above and below the cluster first layer.(b) Oxygen adsorption energy, Eads, vs work function change, as measured by the cluster HOMO, for Pt25/O. The curves refer to the cluster with point charges (PC). Both Stark and full SCF curves are shown G. Pacchioni, F. Illas, S. Neophytides, and C.G. Vayenas, Quantum-Chemical Study of Electrochemical Promotion in Catalysis, J. Phys. Chem. 100, 16653-16661 (1996).

  42. POTENTIAL AND WORK FUNCTION EFFECT ON CATALYTIC RATES:ELECTROPHOBIC, ELECTROPHILIC, VOLCANO & INVERTED VOLCANO REACTIONS P=DF/kbT=eDUWR/kbT

  43. ELECTROPHOBIC REACTIONS

  44. RULES OF PROMOTION IN TERMS OF ADSORPTION COEFFICIENTS S. Brosda, C.G. Vayenas and J. Wei, Appl. Catalysis B, 68, 109-124 (2006).

  45. EFFECTIVE DOUBLE LAYER (EDL) ISOTHERM

  46. EDL KINETICS PREDICTION OF ELECROPHOBIC, ELECTROPHILIC, VOLCANO AND INVERTED-VOLCANO BEHAVIOUR kD= 100 kA= 0.01 Electrophilic kD= 0.01 kA= 100 Electrophobic kD= 0.01 kA= 0.01 Inverted volcano-type kD= 100 kA= 100 Volcano- type λD= 0.15, λA=-0.15, pD= 1, pA= 1

  47. EDL SIMULATION OF CO OXIDATION KINETICS ON Pt/ -Al2O3 I.V. Yentekakis, G. Moggridge, C.G. Vayenas, and R.M. Lambert, J. Catal. 146, 292-305 (1994). C.G. Vayenas, S. Bebelis, C. Pliangos, S. Brosda, and D. Tsiplakides, The Electrochemical Activation of Catalysis, Kluwer Academic/Plenum publishers (2001)

  48. Monolithic Electropromoted Reactor (MEPR) Solid electrolyte:YSZ, 8wt.% Y2O3 1mm thickness Ceramic Reactor Casing Multiple carved grooves in the two vertical opposing walls serve as receptors of the electrocatalytic elements. The catalyst elements are covered on both sides by thin, porous and conductive catalyst layers. S. Balomenou, D. Tsiplakides, A. Katsaounis, S. Thiemann-Handler, B. Cramer, G. Foti, Ch. Comninellis and C.G. Vayenas, Applied Catalysis B: Environmental, 52 (2004) 181.

  49. Monolithic Electropromoted Reactor (MEPR)

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