Modelling alkali promotion in heterogeneous catalysis: in situ electrochemical control of catalytic reactions

LAMBERT, R M; WILLIAMS, F J; PALERMO, A; TIKHOV, M S

TOPICS IN CATALYSIS

SPRINGER/PLENUM PUBLISHERS

Año: 2000 vol. 13 p. 91 - 98

1022-5528

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.