Modelling alkali promotion in heterogeneous catalysis: in situ electrochemical control of catalytic reactions
- 134 Downloads
Electron spectroscopic data and reactor measurements show that electrochemical promotion (EP) of thin film catalysts deposited on solid electrolyte supports is the result of spillover phenomena at the three‐phase boundary between the electrolyte, the catalyst and the gas phase. Ions from the electrolyte are discharged at the electrode/electrolyte interface and migrate to cover the catalyst surface whose properties are thereby strongly altered. The EP effect and the phenomena that underlie it are illustrated here by reference to the Na‐promoted catalytic reduction of NO by CO over copper. Electro‐pumping of Na from a β″‐alumina solid electrolyte to the catalyst surface results in large improvements in both activity and selectivity of the latter. Under reaction conditions, the alkali promoter is present as submonolayer amounts of NaNO3 on an oxidised Cu surface. The results indicate that Cu0 sites are not of significance and that the catalytically active surface is dominated by Cu+ and Cu2+ sites. They also show that Cu+ is the critically important site for NO adsorption and that EP is due to Na‐induced enhancement of the adsorption and dissociation of NO at Cu+ sites.
Unable to display preview. Download preview PDF.
- M.P. Kiskinova, Poisoning and Promotion in Catalysis Based on Surface Science Concepts and Experiments (Elsevier, Amsterdam, 1992).Google Scholar
- J.W. Niemantsverdriet, Appl. Phys. A 61 (1995) 503.Google Scholar
- S.J. Thomson, J. Chem. Soc., Faraday Trans. 83 (1987) 2001.Google Scholar
- R.M. Ormerod and R.M. Lambert, in: Surface Reactions, Springer Series in Surface Science, Vol. 34, ed. R.J. Madix (Springer, Berlin, 1994) pp. 89–131.Google Scholar
- M. Konsolakis, L. Nalbantian, N. McLeod, I.V. Yentekakis and R.M. Lambert, Appl. Catal. B (1999), in press.Google Scholar
- S. Wodiunig, F. Bokeloh, J. Nicole and Ch. Comninellis, Electrochem. Solid State Lett. 2 (1999), in press.Google Scholar
- C.G. Vayenas, M. Jaksic, S. Bebelis and Neophytides, in: Modern Aspects of Electrochemistry, eds. O'M Bockris, B.F. Conway and E. White (Plenum, New York, 1995) pp. 57–202.Google Scholar
- C.G. Vayenas and S.G. Neophytides, in: Catalysis, Vol. 12 (Roy. Soc. Chem., Cambridge, 1996) pp. 195–253.Google Scholar
- R.D. Armstrong and M. Todd, in: Solid State Electrochemistry, ed. P.G. Bruce (Cambridge University Press, Cambridge, 1995) p. 277.Google Scholar
- F.J. Williams, M.S. Tikhov, A. Palermo and R.M. Lambert, in preparation.Google Scholar
- C.D. Wagner, in: Practical Surface Analysis by Auger and X-ray Photoelectron Spectroscopy, eds. D. Briggs and M.P. Seah (Wiley, New York, 1983).Google Scholar