Hydrogenation of sulfur dioxide to hydrogen sulfide on chromium promoted Fe/SiO2 catalysts

The hydrogenation of sulfur dioxide to hydrogen sulfide was studied over a series of Fe-Si-Cr catalysts in a flow reactor. These catalysts were prepared by co-precipitation of iron nitrate, sodium silicate and chromium nitrate, which had Cr/Fe atomic ratios of 0–0.04 and Si/Fe atomic ratios of 0–1.2. The addition of Cr and Si dramatically improved the SO2 hydrogenation activity of the iron-based catalyst. The chromia was a textural promoter of iron, increased the catalyst surface area by preventing the iron sintering, and hence resulted in the improved hydrogenation activity. The silica acted as a support for dispersing the active species. The interaction between iron cation and silica was observed by using temperature-programmed reduction (TPR) of the fresh Fe-Si-Cr catalysts. The catalyst with a Fe/Si/Cr atomic ratio of 1/0.6/0.01 had the highest activity, which exhibited much better SO2 hydrogenation activity than the best Fe/γ-Al2O3 catalyst reported before. With a given space velocity, the former catalyst achieved 100% H2S yield at a temperature 50 °C lower than the latter catalyst. X-ray diffraction (XRD) measurements indicated that FeS2 was the active species for SO2 hydrogenation, and the Fe-Si-Cr catalyst had smaller FeS2 crystal size than the Fe/γ-Al2O3 catalyst. The iron–silica interaction and the smaller crystal size might be responsible for the better SO2 hydrogenation activity observed on the Fe-Si-Cr catalyst.