Calorimetric investigation of NO and CO adsorption on Pd100 and
the influence of preadsorbed carbon
J. Chem. Phys., 106 (5):
1990-1996 (1997)DOI: 10.1063/1.473306
Zusammenfassung
The coverage dependencies of the differential heats of adsorption
for CO and NO on Pd100, at room temperature, are reported using
single crystal adsorption calorimetry (SCAC). The initial heat for
CO is 165 kJ/mol, falling markedly with increasing coverage due to
anomalously strong repulsive interactions between molecules. The
formation of a c(2 x 4) overlayer at half monolayer coverage places
severe constraints on the magnitudes of lateral interactions between
adsorbates which can fit the data. A realistic lateral interaction
model is proposed. The influence of predosed carbon on the heat of
adsorption of CO was also investigated. As little as 0.05 ML of C
causes a decrease in the initial heat of about 20 kJ/mol; 0.2 ML
reduces the heat to 120 kJ/mol. The results suggest long range interactions
between C atoms and CO molecules. The initial heat for NO is 155
kJ/mol, decreasing smoothly to about 105 kJ/mol at saturation. The
coverage dependencies of the sticking probabilities for both NO and
CO exhibits precursor behavior which is considerably diminished in
the presence of a high C precoverage.