Palladium–Iron Bimetal Sorbents for Simultaneous Capture of Hydrogen Sulfide and Mercury from Simulated Syngas

Abstract

Fe2O3/γ-Al2O3, PdO/γ-Al2O3, and PdO–Fe2O3/γ-Al2O3 sorbents were prepared using the pore volume impregnation method. Experiments to study the removal of Hg and H2S from simulated syngas were carried out using a conventional flow-type packed-bed reactor system over the temperature range of 100–300 °C. Sorbents before and after the adsorption of Hg and H2S were analyzed by Raman spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The experimental results show that the bimetal oxide PdO–Fe2O3/γ-Al2O3 sorbent can simultaneously remove Hg and H2S in syngas and the operation temperature can be as high as 200–300 °C. The high efficiency of Hg removal by PdO/γ-Al2O3 and H2S removal by Fe2O3/γ-Al2O3 enhances the ability of PdO–Fe2O3/γ-Al2O3 to remove Hg and H2S simultaneously at a relatively high temperature. H2 and CO can enhance the efficiency of the removal of Hg over the PdO–Fe2O3/γ-Al2O3 sorbent at 250 °C, but there is apparently no influence on the removal of H2S. On the basis of the analysis of the different capture performances for Hg and H2S between PdO/γ-Al2O3 and PdO–Fe2O3/γ-Al2O3, there are two possible mechanisms for the capture of Hg over bimetal oxides, namely, by formation of HgS or HgO and Pd–Hg amalgam. The reactions of Hg (adsorbed on the surface of the sorbent) with Pd (formed by reduction of PdO) and Sad [formed by the reaction of H2S with lattice oxygen in Fe2O3 (3H2S + Fe2O3 → 2FeS + Sad + 3H2O)] are the dominant factors.