A study of catalytic reactions of sulphur dioxide and carbon monoxide on perovskite-type compounds of the formula La(1-x)Sr(x)CoO3

Abstract

This work investigates the use of the perovskite-type compound La1-xSrxCoO3 (x = 0.3, 0.5, 0.6, 0.7) as a catalyst for the reaction1SO2 + 2CO > x sx +2CO2Adsorption of SO2 and CO separately on the degassed catalysts at several temperatures, was followed by TPD (temperature programmed desorption), with mass spectroscopic detection of the desorbed species. Trends in the mass changes on adsorption are explained in terms of the changes in reducibility of La1-xSrxCoO3 on changing x.Computation of the SO2 TPD results, which showed two and sometimes three adsorbed species, yielded desorption energies of the range 30-200 kJ mol

.SeveralSO2 and CO mixtures were allowed to flow over La1-xSrxCo03 at various temperatures and flow rates. The removal of SO2 and production of CO2 were followed using gas chromatography and sulphur was collected in a cold trap. LaO.7Srg 3COO3 at 550°C removed SO2 from a stoichiometric mixture of SO2 and CO very efficiently without producing COS. COS production, if it occurs, may be problematical in a commercial SO2 removal application.XRD (X-ray diffraction) revealed that the fresh compounds all had the perovskite-type structure, those exposed to either SO2 or CO retained this structure and those exposed to SO2 and CO together were no longer La, Srx CoO3 XRD of the used catalysts showed theI -x X 3)presence of SrSO4 on those exposed to only SO2 and the presence of sulphides of La, Sr and Co, on those exposed to SO2 and CO. XPS (X-ray photoelectron spectroscopy) of catalysts exposed to SO2 and CO indicated sulphidation, with some sulphate species also present. The results may be explained in terms of the relative oxidizibilitiesof the SO2, CO, SO2 reduced catalyst, 'CO reduced catalyst', 'reactionreduced catalyst' and La1-x Sr Co031x x 3The continuation of the operation of the material for the removal of SO2 suggests that in this instance the active catalyst is no longer a perovskite-type oxide, but possibly a metal sulphide.