A344 Surface Science 156 (1985) 943- 951 North-Holland, Amsterdam
SOME CATALYTIC PROPERTIES SUPPORTED CATALYSTS G.A.
B. C O Q ,
a n d F. F 1 G U E R A S
Laboratoire de Chimie Organique Physique, UR 418. ENS('M, 8 Rue Ecole Normah,. F 34075 Montpellier Cedex, France
and S. F U E N T E S Unwersidad Autonome Metropolitana. lztapalapa, Mexico, DF. Me.rico
Received 9 July 1984; accepted for publication 13 September 1984
Some reactions involving C - H , C C, C CI, C - O bonds are investigated on Rh and Pd supported catalysts in relation with the metallic structure. The general trend is a structure insensitivity for Pd, while the opposite is true for Rh. With the latter metal smalt particles are more active than large particles when the support is silica, but the reverse is true on alumina. The variations of the catalytic properties may he interpreted by a modification of the structure of metal particles.
Surface Science 156 (1985) 952-962 North-Holland, Amsterdam
ADSORPTION-DESORPTION CADMIUM ON NaCI S U R F A C E C.R. HENRY
OF A M O D U L A T E D A T O M I C BEAM OF PARTICLES
and C. CHAPON
Centre de Recherche sur les Mbcanismes de la Croissance ('ristalhne. CNRS, Campus de Lumir~v, Case 913, F-13288 Marseille Cedex 09, France Received 10 July 1984
The modulated molecular beam technique is very efficient in studying surface reactions. It has been applied for measuring adsorption-desorption kinetics of a c a d m i u m vapour on small gold particles deposited on a (100) NaCI surface. The modulation of the incident beam at different frequencies reveals the existence of surface reactions with different rates. At low frequencies ( < 0.1 Hz) one observes slow reactions related to processes occurring at the periphery or on the surface of the gold particles. Thus it has been proved that a part of the cadmium atoms reaching the gold particles is first adsorbed in the capture areas of those particles on the substrate. Measurement of these capture areas around the gold clusters as a function of their size and the substrate temperature gives the mean diffusion length and the difference between adsorption and diffusion energies of the cadmium atoms on NaCI. The relaxation time of the overall process as a function of substrate temperature gives the desorption energy of cadmium atoms from the gold particles.