Hydrothermal Method Prepared Ce‐P‐O Catalyst for the Selective Catalytic Reduction of NO with NH3 in a Broad Temperature Range

Selective catalytic reduction of NOx with ammonia (NH3-SCR) is a widely used process for the abatement of NOx from flue gases and exhaust gases of diesel trucks. The well-known commercial catalysts used for this process are V2O5-WO3/TiO2 or V2O5-MoO3/TiO2 which function within a relatively narrow temperature window of 300–400 8C. As the temperature rises above 400 8C, V-based catalysts exhibit a rapid decrease in activity and selectivity in the reduction of NOx due to the oxidation of SO2 into SO3. [2] Furthermore, the emissions of toxic vanadium lead to health problems. In addition, deactivation by poisoning is another problem because flue gases contain metal oxides (e.g. , K2O) that deactivate V-based catalysts. Therefore, alternative NH3-SCR catalysts with only nontoxic components and stable under harsh operating conditions are required. Low-temperature SCR catalysts, such as amorphous MnOx, [5] Fe–Mn–Ox, [6] MnOx–CeO2, [7] Mn/TiO2, [8] are urgently needed for the abatement of NOx from flue gases to avoid reheating of the gas and thus decrease the capital cost. In the medium temperature range, Fe-based catalysts, such as Fe2O3– WO3/ZrO2, [9] and crystallite iron titanate, exhibit excellent SCR activity. However, these catalysts regularly have problems with low N2 selectivity, H2O and SO2 deactivation, and especially the loss of activity at high temperature and high space velocity. For the high temperature range, some zeolite catalysts, such as Fe-ZSM-5 reported by Long et al. and Carja et al. , have shown highly catalytic performance in the range of 400– 500 8C. However, their applications are greatly restricted by poor hydrothermal stability of the zeolite support. A comprehensive overview of the NH3-SCR reaction mechanism shows that both surface acidity and redox property are necessary for the NH3-SCR reaction. Herein, several metal phosphate catalysts containing different multivalent ions, (M–P–O; M = Cu , Fe + , Mn + , Ce), were prepared. The most promising catalyst, Ce-P-O, is emphasized herein due to its high deNOx activity. The results showed that Ce-P-O(h), prepared by a hydrothermal method (see the Supporting Information), is a novel and efficient catalyst for NH3-SCR with NO conversions above 90 % within the range of 200–550 8C. For comparison, the Ce-P-O catalyst was also prepared by a coprecipitation method and denoted as Ce-P-O(c). Figure 1 shows the comparison of deNOx activities of Ce-P-O catalysts as a function of reaction temperature. Ce-P-O catalysts prepared by hydrothermal and coprecipitation methods exhibited different deNOx performance in low temperatures

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