Competitive adsorption study of CO 2 and SO 2 on Co II3[Co III(CN) 6] 2 using DRIFTS

Abstract

Diffuse reflectance infrared Fourier transform spectroscopy was used to study the competitive adsorption of CO 2 and SO 2 on the cobalt Prussian blue analogue Co II 3[Co III(CN) 6] 2 at 298 K. Characteristic peaks for adsorbed CO 2 and SO 2 species were identified and their relative areas, measured simultaneously as a function of pressure at 298 K, varied in accordance with a Langmuir–Freundlich isotherm fitted to both gases in the low-coverage Henry's Law limit. Evidence for co-adsorption of trace water was also obtained, as well as the apparent formation of an analogous cobalt nitroprusside compound as a reaction product under certain conditions. The several aspects of the adsorption of CO 2 and SO 2 determined in this work point to an important role for real-time diffuse reflectance infrared measurements in adsorption studies, particularly in the case of competitive adsorption where the occurrence and fate of molecular-level markers arising from more than one adsorbed species can be monitored simultaneously. Depending on the application, this may more than offset certain quantitative limitations of the technique that confine measurements to a relatively narrow set of experimental conditions and demand careful consideration of the effects of sample preparation and treatment.