Study On Preparation Of Nanometer MgO As Support Of Ru-based Catalyst By Microwave And Its Morphology And Properties

Microwave technique was introduced to prepare nano-MgO which acted as thesupport of Ru-based catalyst for ammonia synthesis in this paper. The preparationconditions were studied to maximize the activity of ammonia synthesis. The nano-MgOsupport and Ru catalyst were characterized by N₂ physical adsorption, CO chemicaladsorption, X Ray Diffraction (XRD) for powder, SEM and EDS etc. Their catalyticactivity was evaluated by high-pressure micro-reactor system.MgO prepared by microwave technique showed a highly distributing surface, largesurface area and developed micropore, and its average diameter is about 30-60nm whichis among the nanoolevel. It should be the excellent support for Ru catalyst. The XRDexperiments of MgO prepared b.y usual method and microwave technique showed thatMgO prepared by microwave technique had stronger BaCO₃ peaks than MgOprepared by usual method.The catalytic activity of Ru-based catalysts for ammonium synthesis was sensitiveto their preparation conditions of MgO. The suitable conditions are as follows: thepower was 270W for preparation nano-MgO by microwave technique; treating time was30-40 minutes; calcination temperature was 600℃; mole ratio of Mg to Ba was 1:0.20;mole ratio of Mg to NH₃ in aqueous ammonia was 1:8; washing by low-concentrationammonia solution instead of organic solvent could obtain better support.The kinetics of Mg(OH)₂ decomposition into MgO in calcination process wasinvestigated by TG/DSC systemically. The result showed that Mg(OH)₂ decomposingpeak was about 342.3℃, and its decomposing temperature was between 273℃and427℃with the weight loss of 25.9%. According to the diameter change of MgOcrystals with calcination temperature and time, the kinetics equation of growth ofnano-MgO crystals was G⁴=6.51×10⁶ t exp(-39700/RT) nm⁴·h^-1.The experiments indicated that not only in the process of nano-MgO preparation,but also in impregnation of Ru active components, addition Of surfactants could achieveuniform and smooth surface for Ru catalyst, and its activity was improved to some degree.For instance, with the addition of OP-10 during preparation of nano-MgO, the activityof corresponding catalyst was as high as 11.38% under the condition of 475℃, 10 MPaand 10000 h^-1 which is 17% higher than the catalyst free of surfactant.