To develop a highly reactive and easily regenerable zinc oxide high-temperature desulfurization sorbent, a modification of ZnO−TiO2 by addition of ZrO2 was studied. The metal oxides ZnO−TiO2−ZrO2 were prepared by a coprecipitation method:  the amount of ZnO was a fixed 50 mol % of the sample. In this study, it was found that the addition of 5 or 10 mol % ZrO2 to 50 mol % ZnO−50 mol % TiO2 greatly improved the reactivity for H2S removal. Furthermore, the addition of ZrO2 improved its regenerability: the temperature for the regeneration of the sample was decreased to ca. 40 °C in the absence of H2O and ca. 75 °C in the presence of 10% H2O by the addition of 10% ZrO2.

To develop an easily regenerable zinc oxide high-temperature desulfurization sorbent, the role of H2O in the course of oxidative regeneration of zinc sulfide in the presence of O2 were studied using ZnO without support material as a sorbent. Oxidative regeneration of ZnS in the presence of water vapor was examined using TPR technique and H2 18O. From this study, the following results were obtained:  ZnS was converted to SO2 and H2 by H2O in the absence of O2 at high temperature (> ca. 600 °C); in the first step in the oxidative regeneration, ZnS predominantly reacted with H2O more than O2; the SO2 formed from ZnS contained oxygen from H2O. From the experimental results, it was found that the oxidative regeneration of ZnS in the presence of H2O and O2 can be expressed by the following two equations:  ZnS + 3H2O ⇔ ZnO + SO2 + 3H2; 3H2 + 3/2O2 ⇒ 3H2O. In the absence of H2O or in the case of very low value of H2O/O2 concentration ratio, the following reaction also occurred:  ZnS + 3/2O2 ⇒ ZnO + SO2

To develop a highly active calcium oxide high-temperature desulfurization sorbent, a method of preparation of macroporous calcium oxides from lime was studied. This method is composed of two steps:  swelling of the lime and calcination of the swelled sample. Swelling occurred when lime was exposed to the vapor of acetic acid. The swelling resulted from calcium acetate formation in the sample. The swelling rate was at a maximum in the presence of acetic acid and depressed by the presence of water vapor. The swelled sample was converted to macroporous calcium oxide by heating to 850 °C. The reactivity of the macroporous calcium oxide for the removal of SO2 or H2S in the presence of H2O vapor was higher than that of the calcined raw limestone. In particular, its SO2 removal capacity and the oxidative character of CaS to CaSO4 and CaO were greatly improved by this swelling method. These characteristics were also compared with those of a sample prepared from limestone by this swelling method.

To understand the contribution of lime to the abatement of N2O emission from fluidized coal combustor, the catalytic activity of the lime for the decomposition of N2O under coal combustion conditions was studied. Lime was active for the catalytic decomposition of N2O, and its activity was stable in the simulated coal combustion flue gas in the absence of SO2 at 800 °C. The catalytic activity of lime was depressed by the presence of CO2, H2O, and SO2. The affect of the presence of SO2 seemed to be most important:  the catalytic activity of the lime gradually decreased as the degree of sulfation increased, and the specific surface area decreased with the progression of sulfation. From N2O pretreatment and temperature-programmed desorption studies on the used lime, it was found that two oxygen species and one species of NO desorbed. A surface character change due to sulfation is expected from these gas desorptions. From the relation of the activity to the surface area or the desorption of the gases or both, it was concluded that a decrease in the surface area contributed to the decay of the activity more effectively than the surface character change caused by the sulfation.

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