Ca-type todorokite catalysts were designed and prepared by a simple redox method and applied to the selective reduction of NO by NH (NH-SCR) for the first time. Compared with the Na-type manjiroite prepared by the same method, the todorokite catalysts with different Mn/Ca ratios showed greatly improved catalytic activity for NO reduction. Among them, Mn8Ca4 catalyst exhibited the best NH-SCR performance, achieving 90% NO conversion within temperature range of 70-275°C and having a high sulphur resistance. Compared to the Na-type manjiroite sample, Ca-type todorokite catalysts possessed an increased size of tunnel, resulting in a larger specific surface area. As increased the amounts of Ca doping, the Na content in Ca-type todorokite catalysts significantly decreased, providing larger amounts of Brønsted acid sites for NH adsorption to produce NH. The NH species were highly active for reaction with NO + O, playing a determining role in NH-SCR process at low temperatures. Meanwhile, larger amounts of surface adsorbed oxygen contained over the Ca-doping samples than that over Na-type manjiroite, promoting the oxidation of NO and fast SCR processes. Over the Ca-type todorokite catalysts, furthermore, nitrates produced during the flow of NO + O, were more active for reaction with NH than that over Na-type manjiroite, benefiting the occurrence of NH-SCR process. This study provides novel insights into the design of NH-SCR catalysts with high performance.
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Design of Ca-type todorokite catalysts with highly active for the selective reduction of NO by NH at low temperatures.
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Ca-type todorokite catalysts were designed and prepared by a simple redox method and applied to the selective reduction of NO by NH (NH-SCR) for the first time. Compared with the Na-type manjiroite prepared by the same method, the todorokite catalysts with different Mn/Ca ratios showed greatly improved catalytic activity for NO reduction. Among them, Mn8Ca4 catalyst exhibited the best NH-SCR performance, achieving 90% NO conversion within temperature range of 70-275°C and having a high sulphur resistance.
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