| Research Abstract |
For the purpose of uncovering the cause of synergy at molecular level, creation of new synergy was attempted using a complex metal cluster synthesized from chelating agent, metal complex and metal ion. We found the promoting effect of nitrilotriacetic acid (NTA)on hydrodesulfrization (HDS) activity of cobalt-molybdenum/alumina (Co-Mo/Al_2O_3) catalyst. Selective synthesis of synergistic site (active site) was enhanced when Co-Mo/Al_2O_3 catalysts were prepared by an impregnation method using NTA as chelating agent. In this study it was found that EDTA and trans-1,2-cyclohexane diamine-N,N,N^1, N^1-tetra-acetic acid (CyDTA) shows higher promoting effect. HDS activity of Cy-DTA-Co-Mo/Al_2O_3 was 70% higher than that of Co-Mo/Al_2O_3. Incorporation of these chelated complex into zeolite cage nor synthesis of complex chelate cluster in the cage was not confirmed.
In order to inverstigate the mechanism of activity promotion, IR spectra were measured to examine the behavior of adsorbed NO on
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the promoter and Mo sites. Mo K-edge EXAFS was also measured for clarify the local structure of active site. While HDS activity per CUS was increased, the effect of chelating agent vary greatly in dispersion of MoS2 cluster which is presumed to support the active site under reaction conditions, and in the number of coordinatively unsaturated site (CUS). It was suggested that highly dispersed cobalt is essential for formation of active site. Thus, it was demonstrated that dispersion of coblat is enhanced by chelating agent without changing local structure of active site.
HDS activity of nickel-molybdenum/alumina (Ni-Mo/Al_2O_3) and nickel-tungsten/alumina (Ni-W/Al_2O_3) was compared with that of Co-Mo/Al_2O_3. While in the case of Ni-Mo/Al_2O_3, HDS activity was not influenced by NTA nor CyDTA addition, that of Cy-DTA-Ni-W/Al_2O_3 was 60% higher than that of Ni-W/Al_2O_3. The result shows that combination of metal ion is one of an important factor for the promotion effect of chelating agent. Less
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