Surface behaviour of carbon supported ruthenium catalysts

Abstract

Chemisorption of H 2, CO, CO 2 and N 2 on carbon-supported ruthenium catalysts, with and without alkali promoters, was studied to ascertain the nature of binding of these gases to the catalyst surface. It was observed that the chemisorption of hydrogen is significantly enhanced when a carbon-supported ruthenium catalyst is promoted either with K 2O or K 2 O + BaO. This enhancement may be due to the penetration of some of the hydrogen atoms to lower crystal planes of the catalyst, or some of the hydrogen atoms were migrated to ruthenium atoms lying immediately below the surface promoter molecules. In contrast, nitrogen chemisorption is reduced on the promoted catalysts but shows higher activity for ammonia synthesis. Presorption experiments indicated an inhibiting effect of nitrogen on hydrogen chemisorption. This effect, which was approximately one to one, suggests that the chemisorbed nitrogen occupied the same surface sites. Data on adsorption of N 2, H 2 and CO and their mutual inhibiting effects led to the conclusion that the chemisorption of nitrogen and hydrogen on the transition metal surface was predominantly of atomic nature while that of carbon monoxide was molecular. Carbon dioxide, however, was sorted molecularly by the alkali-containing molecules. There appeared to be significant influence of the surface acidity-basicity functions of the support material on the chemisorption of nitrogen on ruthenium catalysts.