New sulfur adsorbents derived from layered double hydroxides: II. DRIFTS study of COS and H2S adsorption

H2S and COS adsorption were studied on two calcined layered double hydroxides (LDHs), Mg0.75Al0.25(OH)2(CO3)0.125 and Mg0.65Al0.35(OH)2(CO3)0.175, using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and a chemisorption apparatus. Both demonstrated the ability to irreversibly adsorb H2S, corresponding to uptakes of 1.54 and 1.76 μmol/m2, respectively, but Mg0.75Al0.25 had a significantly larger capacity for COS, 1.62 μmol/m2 compared to 0.80 μmol/m2 for Mg0.65Al0.35. Analysis of the DRIFT spectra suggests the adsorption of H2S proceeds via the substitution of lattice oxygen with sulfur, resulting in the formation of H2O on the surface. COS adsorption is more complicated, although it appears that a similar substitution of lattice oxygen with sulfur occurs. This results in the formation of CO2 and subsequently bicarbonates and carbonates. The formation of hydrogen thiocarbonate is also involved, although this form is generally only observed in the later stages of adsorption and appears to form at the expense of bicarbonate. The Mg0.75Al0.25 LDH retained its ability to adsorb COS in the presence of propene.