Ca-type todorokite catalysts were designed and prepared by a simple redox method and applied to the selective reduction of NO_(x) by NH_(3)(NH_(3)-SCR)for the first time.Compared with the Na-type manjiroite prepared b...Ca-type todorokite catalysts were designed and prepared by a simple redox method and applied to the selective reduction of NO_(x) by NH_(3)(NH_(3)-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_(x) reduction.Among them,Mn8Ca4 catalyst exhibited the best NH_(3)-SCR performance,achieving 90%NO_(x) conversion within temperature range of 70-275℃ 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 Bronsted acid sites for NH_(3) adsorption to produce NH_(4)^(+).The NH_(4)^(+)species were highly active for reaction with NO+O_(2),playing a determining role in NH_(3)-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_(2),were more active for reaction with NH_(3) than that over Na-type manjiroite,benefiting the occurrence of NH_(3)-SCR process.This study provides novel insights into the design of NH_(3)-SCR catalysts with high performance.展开更多
Single phase and well-crystallined todorokite were synthesized by heating and refluxing process from birnessite as a precursor. The average chemical composition of the synthesized todorokites by refluxing for 8 h and ...Single phase and well-crystallined todorokite were synthesized by heating and refluxing process from birnessite as a precursor. The average chemical composition of the synthesized todorokites by refluxing for 8 h and for 24 h was Mg0.19MnO2.11(H2O)1.15 and in0.17-MnO2.10(H2O)0.88, respectively. The crystallinity of the todorokite increased and no other phase was produced with increasing refluxing period. The synthesized todorokites have the same morphologies and the similar structural characteristics with the natural todorokites and hydro-thermally synthesized samples. The chemical compositions of the synthetic tordorokites by refluxing process are close to those of todorokites synthesized by hydrothermal process, except a higher average oxidation state of Mn for the former.展开更多
Todorokite commonly occurs in Earth surface environments. The factors governing formation of todorokite, such as reaction temperature, metal ions, dissolved O2 and pH, were investigated in this paper. Results showed t...Todorokite commonly occurs in Earth surface environments. The factors governing formation of todorokite, such as reaction temperature, metal ions, dissolved O2 and pH, were investigated in this paper. Results showed that the forming rate of todorokite and its crystallinity decreased with falling reaction temperature, and the effect of temperature was more significant than that of other parameters. Nature of metal ions in the interlayer of buserite precursor and the structure of the buserite precursor obviously affected buserite transformation into todorokite. Weak bonding between the metal ions and MnO6 layer of buserite was favorable to todorokite formation. The rate of todorokite formation was promoted at a lower temperature with appropriate bubbling of O2. The pH in the system slightly influenced the todorokite formation, and todorokite could also be formed in a weak alkali medium or in a slightly acidic medium. Aged buserite pre-cursor more easily form todorokite than the unaged one.展开更多
Manganese minerals in the polymetallic nodules from the Central Pacific Ocean were studied using electron microscopy. The principal Mn minerals, being vernadite and todorokite, exhibit different electron diffraction p...Manganese minerals in the polymetallic nodules from the Central Pacific Ocean were studied using electron microscopy. The principal Mn minerals, being vernadite and todorokite, exhibit different electron diffraction patterns and morphological features. According to its morphological feature, todorokite shows three phases: fibrous, lamellar and lath-shaped. Both vernadite and todorokite are authigenic minerals. While vernadite was mainly precipitated directly from the relevant solution by microbiological oxidation, todorokite was separated from the solution chemically without the help of microbe. Hence, these two minerals show a close genetic relation.展开更多
基金supported by Self-deployed Projects of Ganjiang Innovation Academy,Chinese Academy of Sciences(No.E055C003)the National Natural Science Foundation of China(Nos.U20B6004 and 22072179)
文摘Ca-type todorokite catalysts were designed and prepared by a simple redox method and applied to the selective reduction of NO_(x) by NH_(3)(NH_(3)-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_(x) reduction.Among them,Mn8Ca4 catalyst exhibited the best NH_(3)-SCR performance,achieving 90%NO_(x) conversion within temperature range of 70-275℃ 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 Bronsted acid sites for NH_(3) adsorption to produce NH_(4)^(+).The NH_(4)^(+)species were highly active for reaction with NO+O_(2),playing a determining role in NH_(3)-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_(2),were more active for reaction with NH_(3) than that over Na-type manjiroite,benefiting the occurrence of NH_(3)-SCR process.This study provides novel insights into the design of NH_(3)-SCR catalysts with high performance.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.40101017 and 40071048) by the Research Fund for the Doctoral Program of Higher Education(Grant No.2002050411).
文摘Single phase and well-crystallined todorokite were synthesized by heating and refluxing process from birnessite as a precursor. The average chemical composition of the synthesized todorokites by refluxing for 8 h and for 24 h was Mg0.19MnO2.11(H2O)1.15 and in0.17-MnO2.10(H2O)0.88, respectively. The crystallinity of the todorokite increased and no other phase was produced with increasing refluxing period. The synthesized todorokites have the same morphologies and the similar structural characteristics with the natural todorokites and hydro-thermally synthesized samples. The chemical compositions of the synthetic tordorokites by refluxing process are close to those of todorokites synthesized by hydrothermal process, except a higher average oxidation state of Mn for the former.
基金supported by the National Natural Science Foundation of China(Grant No.40403009)by the Research Fund for the Doctoral Program of Higher Education(Grant No.2002050411).
文摘Todorokite commonly occurs in Earth surface environments. The factors governing formation of todorokite, such as reaction temperature, metal ions, dissolved O2 and pH, were investigated in this paper. Results showed that the forming rate of todorokite and its crystallinity decreased with falling reaction temperature, and the effect of temperature was more significant than that of other parameters. Nature of metal ions in the interlayer of buserite precursor and the structure of the buserite precursor obviously affected buserite transformation into todorokite. Weak bonding between the metal ions and MnO6 layer of buserite was favorable to todorokite formation. The rate of todorokite formation was promoted at a lower temperature with appropriate bubbling of O2. The pH in the system slightly influenced the todorokite formation, and todorokite could also be formed in a weak alkali medium or in a slightly acidic medium. Aged buserite pre-cursor more easily form todorokite than the unaged one.
文摘Manganese minerals in the polymetallic nodules from the Central Pacific Ocean were studied using electron microscopy. The principal Mn minerals, being vernadite and todorokite, exhibit different electron diffraction patterns and morphological features. According to its morphological feature, todorokite shows three phases: fibrous, lamellar and lath-shaped. Both vernadite and todorokite are authigenic minerals. While vernadite was mainly precipitated directly from the relevant solution by microbiological oxidation, todorokite was separated from the solution chemically without the help of microbe. Hence, these two minerals show a close genetic relation.
