| Ruthenium catalysts have come to be used as the second-generation ammonia catalysts after the iron catalyst. The characteristic feature of ruthenium catalyst is the high activity under low-temperature and low-pressure. In this paper, we prepared a series of ruthenium catalysts by impregnation, aiming at investigation the effect of promoter and supports on catalyst activity. The factors that influence the activity of the catalysts were discussed and the probably promoted mechanism of potassium fluoride was studied.Unpromoted magnesia-supported and ceria-supported ruthenium catalysts with different Ru-loading were prepared. The catalyst with 4 wt% Ru-loading exhibited the highest activity.Magnesia and lanthanide oxides were used as the support of ruthenium catalysts. In comparison, we found the activity of lanthanide oxides-supported Ru catalysts was superior to other metal oxide-supported ones such as Ru/MgO. Especially, ceria was more effective than other lanthanide oxide for ammonia synthesis when used as the support. Under the reactive condition, maybe the lanthanide oxide was reduced. Partially reduced lanthanide oxide donates electrons to Ru atom, forming the active site.Lanthanide oxides are effective promoters for Ru/MgO. They might induce similar electron-donating effect to Ru on magnesia as alkali metal. However, the promoting effect of lanthanides cannot be completely explained on the basis of their electron-donor ability only. Other studies seems to show that the effect of these elements, might decrease the hydrogen competition during nitrogen adsorption.Ruthenium is known to be active for dissociation of dinitrogen. Basic promoter is desirable because of inducing electron-donating effect. Strong basic materials such as alkali metal compounds increase the activity of ammonia synthesis under atmospheric pressure remarkably. In this paper, different potassium-promoted magnesia-supported ruthenium catalysts were compared. The activity for ammonia synthesis of potassium fluoride-promoted Ru catalyst is much higher than that of potassium oxide-promoted Ru catalyst.What induce the different activities for ammonia synthesis between KF-Ru/MgO and K2O-Ru/MgO? By TEM, XRI^ N2-TPD and XPS, the probably promoted mechanism of potassium fluoride was studied.The TEM micrographs showed that potassium fluoride-promoted Ru catalyst improved resistance to metal sintering, which means KF has structural promoting effect.The XRD analysis of reduced ruthenium catalysts showed that Ru was present as metal. In the pattern of K-promoted catalysts, no reflections corresponding to any K-based phase were ever observed, very likely due to the high dispersion of the precursors. Compared the Ru diflractive intensities of Ru/MgCK K2O-Ru/Mg(X KF-Ru/MgO, we found that the diflractive signal of Ru (002) surface decreased for K2O-ru/MgO and disappeared for KF-Ru/MgO. We considered Ru (002) surface, probably, is one of the active sites of Ru catalysts.The N2-TPD results indicated that the nitrogen-desorbed temperature decreased as potassium. It means that potassium promoter decreased the energy of N2 adsorption and activation, confirmed the electron-donating effect of potassium. From the graphs of N2-TPD, we observed two peaks. It suggested that there have two different active sites for dinitrongen absorption on Ru catalyst. The one is Ru (0001) surface containing special Bs-type site, the other have not been reported.We studied the elements on the catalysts surface by XPS. In comparison, we found the relative concentration of potassium on K2O-Ru/MgO surface is much higher than the concentration of potassium on KF-Ru/MgO surface. Therefore, we educed that the lower promoting efficiency of K2O, in comparison to KF, is very likely due to its excessive concentration on the surface, covering a larger fraction of Ru active sites. Furthermore, the K+F coadsorbate is able to induce a reconstruction of the Ru surface, whereby the number of active sites are increased.Adsorption spectra of atom and molecule are often us...
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