Perovskite LaFeO 3 /ZSM-5 is synthesized via citrate route for H 2 S removal at high temperatures. It shows good thermal stability after heat treatment at 500–700 ∘ C with respect to slight changes in crystallographic phase and textural property. It presents the optimal desulfurization performance at 600 ∘ C with sulfur capacity of 1017 μ mol S/g and products of S, LaS 2 , and Fe 7 S 8 . Sulfidation at 500 ∘ C yields the same products as sulfidation at 600 ∘ C but displays the lowest sulfur capacity of 408 μ mol S/g. Sulfidation at 700 ∘ C produces La 2 O 2 S, Fe 3 S 4 , and unreacted LaFeO 3 . The activation energy of the sulfidation reaction over LaFeO 3 /ZSM-5 is 109.6 kJ/mol.
The high-temperature H 2 S removal was conducted over x La y Cu/ZSM-5 sorbents prepared via citric acid method. The sorbents showed good desulphurization performance, the maximal sulfur capacity of 2240.5 μmol S/g over 5La5Cu/ZSM-5 was achieved at 700 °C. The presence of H 2 obviously shortened the breakthrough time and reduced the sulfur capacity. However, the presence of CO had little influence on the desulphurization behavior. The sulfidation activity of La 2 O 3 can be significantly enhanced by introduction of Cu due to the intimate mixing of La 2 O 3 and CuO, the formation of La 2 CuO 4 compound.
Sulfides existing in many gas mixtures of high temperature cases have a negative effect on various industrial applications. In this study, we present samarium-doped cerium (SDC) sorbent to remove H 2 S at high temperature. Compared with pure CeO 2 , the SDC sorbent shows excellent ability in sulfur removal because of the positive effect of the doping of Sm. The H 2 has a negative influence on sulfidation of the SDC sorbent and significantly shortens the breakthrough time, hence breakthrough sulfur capacity (BSC). The carbon monoxide present in the feed gas has no obvious effect on the sulfur-removal performance. A suitable samarium loading in SDC leads to an optimum interaction between metal oxide species and the surface oxygen vacancies , which results in an optimal adsorbed activity of reduced gas (H 2 , H 2 S) and hence desulphurization performance. In addition, the SDC sorbents have a good regenerated ability by a simple calcination process.
x Ce y Mn/ZSM-5 sorbents were prepared using sol–gel method and employed for H 2 S removal in the temperature range of 600–800 °C. The sorbents exhibited high performance in sulfur removal due to the cooperative effect of CeO 2 and MnO x . The presence of H 2 was unfavorable for sulfidation and obviously shortened the breakthrough time and reduced the sulfur capacity. However, the existence of CO had little impact on the sulfur-removal performance. The characterization results revealed that the ZSM-5 structure remained intact during preparation and sulfidation process. And active species, such as CeO 2 and Mn 2 O 3 , were well dispersed on ZSM-5, which would suppress the mechanical disintegration and improve the thermal stability of x Ce y Mn/ZSM-5.
Performance of CeO 2 -La 2 O 3 /ZSM-5 sorbents for sulfur removal was examined at temperature ranging from 500 oC to 700 oC. The sulfur capacity of 5Ce5La/ZSM-5 was much bigger than that of CeO 2 /ZSM-5. H 2 had a negative impact on the sulfidation; however, CO had little influence on sulfur removal. The characterization results showed that CeO 2 and La 2 O 3 were well dispersed on ZSM-5 because of the intimate admixing of La 2 O 3 and CeO 2 , the major sulfidation products were Ce 2 O 2 S and La 2 O 2 S, the XRD and SEM results revealed that ZSM-5 structure could remain intact during preparation and sulfidation process, the H 2 -TPR showed that the reducibility of CeO 2 can be remarkably enhanced by addition of La.
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