On the initial deactivation of MnxOy–Al2O3 sorbents for high temperature removal of H2S from producer gas

• Initial capacity can be predicted by oxygen chemisorption assessing the Mn dispersion.
• Sorbent capacity loss during 13 cycles increases with Mn loading.
• Prereduction with H2 lowers initial sorbent capacity substantially.
• Deactivation mechanisms include changes in the alumina structure.

MnxOy−Al2O3 sorbents with Mn loadings of 15 and 30 wt.% were prepared by wet impregnation using Mn(NO3)2.4H2O precursor and γ-alumina. After calcination at 600 °C in air and reduction in H2/N2, the solids were tested for the removal of H2S from a model, dry producer gas with a composition of 0.4 vol.% of H2S in 40 vol.% of H2, the balance being inert gas (N2 and Ar). Regeneration was performed with 10 vol.% O2 in N2 at 450 °C, which was the same temperature as that used for the H2S uptake measurements. 13 sorption/regeneration cycles were performed. The initial sorption capacity adjusted for the Mn content was similar for the two samples, which is in agreement with comparable chemisorption values obtained from O2 pulse chemisorption measurements. The fresh and the tested samples were characterized by N2 sorption, XRD, Raman spectroscopy and TPR. During the testing, an overall deactivation was observed which was more pronounced for the sample with 30 wt.% of Mn. The main reasons for the initial sorbent decay are proposed to be related to an alumina phase transition, transformation of the Mn oxides as well as an incomplete regeneration.