Infra-red spectra of nitrogen adsorbed on silica-supported platinum

Abstract

Infra-red absorption bands of considerable intensity near 2230 cm^–1 have been obtained from nitrogen adsorbed on silica-supported platinum and are assigned to NN bond-stretching vibrations. Samples have been studied with different particle-size distributions, prepared either by impregnation, or homogeneous hydrolysis of hexachloroplatinic acid, or by metal-ammine adsorption. The impregnated catalysts show a high frequency shoulder near 2240 cm^–1 attributed to the presence of additional, but similar, sites present in these catalysts.

The infra-red bands are attributed to reversible weak molecular chemisorption with an isosteric heat of adsorption of 3.6 kcal mol^–1(15 kJ mol^–1). The bands do not occur with hydrogen-covered samples, and the nitrogen adsorption sites are sensitive to contamination. These infra-red absorption bands from adsorbed nitrogen, when corrected for the total areas accessible for adsorption of CO, do not show significant differences of intensity between different sample preparations.