A 5 9 5

Surface Science 223 (1989) 527-550 527 North-Holland, Amsterdam

T H E I S O T O P E E X C H A N G E R E A C T I O N O F C A R B O N M O N O X I D E

O N R u ( 0 0 0 1 ) , (21122) , A N D ( 21110 ) S I N G L E C R Y S T A L S U R F A C E S

T a r o Y A M A D A *, Y a s u h i r o I W A S A W A a n d K e n z i T A M A R U * *

Department of Chemistry, Faculty of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan Received 1 March 1989; accepted for publication 20 July 1989

The kinetics of the catalytic isotope exchange reaction 13C160+ 12C180-'-412C160+ 13C180 were investigated on Ru(0001), (21i22) and (21110) single crystal surfaces. The steady-state rate of 13C180 formation and the isotopic composition of adsorbed CO were measured in the crystal temperature range 400-1000 K and the CO pressure range 10 7-10-3 Pa. The rate-determining step was the adsorption of CO at crystal temperatures above 520 K. There is a fast elementary exchange process on the surface. A detailed discussion is given concerning the surface inter- mediates including CO(B) which is observed as a peak in the thermal desorption spectra at 650 K. The energetics of CO(B) were determined in detail. The effects of step sites and deactivation processes were discussed.

Surface Science 223 (1989) 551-568 551 North-Holland, Amsterdam

P H O T O E L E C T R O N S P E C T R O S C O P I C S T U D I E S O N T H E

D I S S O C I A T I O N O F C O O N P O T A S S I U M - D O S E D R h ¢ l l l ~ S U R F A C E

J f inos K I S S , G f i b o r K L I V I ~ N Y I , Kf i ro ly R I ~ V E S Z a n d F r i g y e s S O L Y M O S I

Reaction Kinetics Research Group of the Hungarian Academy of Sciences and Institute of Solid State and Radiochemistry, University of Szeged, P.O. Box 105, H-6701 Szeged, Hungary Received 7 June 1989; accepted for publication 25 July 1989

Adsorption of CO has been investigated on clean and potassium-dosed R h ( l l l ) surfaces by means of TDS, UPS, XPS and work function measurements. CO adsorbs molecularly at 90-300 K on Rh( l l l ) dosed with K up to a monolayer coverage. No spectroscopic evidences were found for the dissociation of CO in the coadsorbed layer heated to near the onset temperature of CO desorption. A well detectable dissociation of CO was observed following electron bombardment of the coadsorbed layer. The effect of potassium on the reaction of adsorbed oxygen and carbon (produced by electron bombardment or by decomposition of ethylene) was also examined. Formation of chemisorbed CO at 0 K = 0.33 occurred at 400-500 K, far below the desorption of CO from this surface. A promoting effect of potassium was established. It was concluded that CO desorbs from K-dosed Rh( l l l ) without undergoing a significant dissociation, and the isotopic scrambling between labelled CO proceeds likely via a nondissociative mechanism.