Nickel (Ni)-promoted Molybdenum (Mo)-based catalysts are used for hydrotreatment processes in the chemical industry where the catalysts are exposed to high-pressure H₂ at elevated temperature. In this environment, the catalyst transforms into the active phase, which involves the reduction of the oxide. Here, we report on the first in situ study on the reduction of alumina supported Ni- and Mo-based catalysts in 1 mbar H₂ using ambient-pressure X-ray photoelectron spectroscopy (APXPS). The study confirms that mixing Ni and Mo lowers the reduction temperature of both Ni- and Mo-oxide as compared to the monometallic catalysts and shows that the MoO₃ reduction starts at a lower temperature than the reduction of NiO in NiMo/Al₂O₃ catalysts. Additionally, the reduction of Ni and Mo foil was directly compared to the reduction of the Al₂O₃-supported catalysts and it was observed that the reduction of the supported catalysts is more gradual than the reduction of the foils, indicating a strong interaction between the Ni/Mo and the alumina support.

Desulfurization at medium temperature was investigated with focus on impacts of temperature and CO2 concentration under Oxyfuel firing and Regenerative Calcium Cycle (RCC) conditions. Investigation started with thermodynamic analysis and ThermoGravimetric Analysis (TGA). Tests were then conducted by a bench-scale fixed-bed type reactor, using a synthetic gas mixture. Various parameters were evaluated. The envelope covered temperature variation of 150-450 °C, CO2 concentrations in the gas stream up to 60% and water concentrations between 0 to 25%. These tests were done having SO2 concentrations in the gas of 2000 ppm SO2. Furthermore different types of lime samples were screened.It was found that CO2 had strong impact on medium temperature desulfurization. Capture of CO2 by the lime was enhanced by increasing temperature. CO2 competed with SO2 and the relative extent to react with lime varied with temperature. Rate of reaction increased with temperature, the capacity of lime-to-SO2 and lime-to-CO2 increased as well. Optimum temperature windows were searched and will be discussed.Based on the tests results, scenarios of desulfurization options at medium temperature range for Oxy and RCC are evaluated, and will be discussed in details.The testing results show issues related to high concentration of CO2 under the Oxy conditions at temperature over 250 °C. Though capacity of lime for SO2 increases with temperature, the amount is limited due to reaction with CO2 at high concentration. Desulfurization at medium temperature range, 250 - 450 °C, should be aiming at moderate SO2 removal, and the reuse of the spent reagent is considered in the downstream wet desulfurization process.With about 10% CO2, in the RCC conditions, it is more optimistic to remove SO2 in the medium temperature range. Optimum temperature range is discussed for achieving moderate SO2 removal. Reuse of the spent reagent is considered in the downstream wet desulfurization process

With increasing emphasis on the control of greenhouse gases, power plants may move towards oxy-fuel technologies rather than air-fired plants. This move leads to a change in the feed to the desulfurization unit, which also needs to be adapted along with the power plant. Most existing plants already have functioning desulfurization units, which need to be retrofitted for the new conditions. In the present study, three different limes have been examined as sorbents for sulfur capture in oxy-fuel conditions with varying residence times at medium temperature (150–450 ${}^{\circ }$ C). Parameters indicative of the kinetics and competition between SO ${}_2$ and CO ${}_2$ , like SO ${}_2$ breakthrough time, total lime conversion, yield for sulfur capture and sulfur selectivity have been evaluated. The results of this study lead to the recommendation that medium temperature desulfurization should be used for moderate SO ${}_2$ capture, in combination with already existing sulfur capture systems. The effects of CO ${}_2$ and water vapor have also been analyzed. In addition, the performance of the unit irrespective of temperature strongly depends on the lime type. In addition, absence of water vapor strongly favored the desulfurization process when there was high concentration of CO ${}_2$ .