Study of I⁻/I₂ Poisoning of Fe₂O₃-Based Catalysts for the H₂SO₄ Decomposition in the Sulfur−iodine Cycle for Hydrogen Production

Abstract

The poisoning effect of I -/I 2 mixtures on ferrous oxide based catalysts was investigated. These catalysts were used in the sulfuric acid thermal decomposition that is the highest endothermic step in the sulfur-iodine thermochemical cycle for hydrogen production by water splitting. This decomposition reaction needs a temperature as high as 1100 K to occur with a convenient thermodynamic yield for SO 2 formation, and it is affected by kinetic limitations. Therefore only the use of a suitable catalyst allows for a large decrease in the H 2 SO 4 decomposition temperature and attaining reaction yields close to the thermodynamic limits. I 2 and HI present even in traces in the sulfuric acid feeding stream could lead to the poisoning of the catalyst used for the decomposition process and must therefore be minimized. In this study, two Fe 2 O 3 catalysts supported on quartz wool and on alumina were used in the temperature range 873-1073 K in ordinary pressure conditions. The SO 2 formation rates were measured before and after the catalyst poisoning. Kinetics measurements and scanning electron microscopy (SEM) analysis show that I -/I 2 contamination reduced the catalytic activity by modifying its surface properties.

Study on CuO-CeO2/SiC catalysts in the sulfur-iodine cycle for hydrogen production

“…In previous literatures, various evaluations of the SO 3 conversion thermodynamic can be found [3,8,15,[21][22][23][24][25][26][27]. The systematic studies of SO 3 decomposition show the equilibrium conversion ratio is influenced by pressure and temperature dramatically; thus, the partial pressure of gaseous SO 3 in the reactor needs to be carefully considered when a thermodynamic curve is obtained [3,4,24,25]. The CuO-CeO 2 complex oxides catalyst has been widely used in multiple processes, such as water-gas shift reaction [28], SO 2 adsorption [29], and oxidation of CO or methanol [30,31].…”

“…To further improve the activities of various catalysts, the thermodynamic data are thus needed to know the maximum SO 3 conversion ratio. In previous literatures, various evaluations of the SO 3 conversion thermodynamic can be found . The systematic studies of SO 3 decomposition show the equilibrium conversion ratio is influenced by pressure and temperature dramatically; thus, the partial pressure of gaseous SO 3 in the reactor needs to be carefully considered when a thermodynamic curve is obtained .…”

Molten copper hexaoxodivanadate: an efficient catalyst for SO3 decomposition in solar thermochemical water splitting cycles

“…We have recently reported that copper pyrovanadate (Cu 2 V 2 O 7 ) is an efficient catalyst for SO 3 decomposition below 650 °C, 8 temperatures at which most conventional oxide catalysts are less active and less stable. [9][10][11][12][13][14][15][16][17][18] The combination of the pyrovanadate (V 2 O 7 2− ) framework, which is resistant to sulfate formation, and a copper redox species achieves both catalytic activity and stability. The catalytic activity can be enhanced by supporting the catalyst on 3-D mesoporous SiO 2 followed by thermal aging above the melting point of Cu 2 V 2 O 7 (>780 °C).…”

Catalytic Properties of Vanadium Diselenide: A Comprehensive Study on Its Electrocatalytic Performance in Alkaline, Neutral, and Acidic Media

“…Because NSs and NPs did not show any ORR catalytic activity in H 2 SO 4 (data not shown), ORR in alkaline and neutral pHs is reported in this study. The possible reason for the noncatalytic activity of NS and NP in H 2 SO 4 might be surface poisoning by sulfate ions. − The ORR catalytic activities analyzed in KOH and PBS solutions using cyclic voltammograms (CVs) at 10 mV/s scan rate are plotted in Figure a,b, respectively. Figure a clearly shows an anodic shift in the ORR onset potentials of NS and NP in comparison to carbon nanotubes (CNTs), which are close to the Pt/C in KOH solutions (see Figure S5); however, the onset potentials of NS, NP, and CNT are almost similar as the pH decreased to 7.0 (Figure b), indicating the influence of pH on the catalytic activity of VSe 2 .…”