Dissertation
Dissertation > Industrial Technology > General industrial technology > Materials science and engineering > Special structural materials

Influence of La2O3, CeO2 on Preparing the Nanometer Cobalt-based Catalysis Material by the High Energy Ball Mill

Author ZhangQuan
Tutor LiaoShuZhi
School Hunan Normal University
Course Condensed Matter Physics
Keywords high energy ball milling cobalt-base catalyst rare earth oxide mechanism
CLC TB383
Type Master's thesis
Year 2005
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The catalytic conversion of coal into liquid and gaseous fuel by Fischer - Tropsch synthesis (FTS) has been well known for the last 50 years. Today, this procedure is again of great interest, because it is a method of obtaining "clean" fuels and chemicals. Iron, nickel and cobalt catalysts with promoters are most widely used for this reaction The major roles played by these metals or metal ions, in particular, cobalt, are (i) to hydrogenate the dissociating carbon species, (ii) to promote the chain growth and (iii) to restrict the deactivation by carbonaceous deposits. Considering all the mentioned, cobalt-based catalysts are currently the best Fischer - Tropsch catalysts. Promoter, such as ruthenium, zirconia and rare earth oxide like lanthana and ceria, can influence the activity and selectivity of cobalt-based catalysts. In the part, rare earth oxides, such as lanthana and ceria, are studied in the particular as promoters because there are very rich resources in China. Cobalt-based catalysts are often prepared using the incipient wetness impregnation method or spray method and rarely using high energy ball milling. In recent years, high energy ball mill method, which has attract wide attention in the field material field, has been widely applied to produce supersaturated crystalline solid solutions,amorphous phases, nanocrystalline solids and so on.In this paper, the cobalt-based catalytic materials , Co100-x(La2O3x, Co100-x(CeO2x (x=1, 2, 3, ...., 10, 15, 20wt), were prepared by high energy ball mill method and the effects of the rare earth oxides(La2O3, CeO2) addition on cobalt-based catalytic materials during the process of high energy ball milling was studied. The crystal sizes and stresses caused by mechanical alloying of these powders were studied by the X-ray diffraction.It was showed that crystal size of Co96(La2O34 powders (Co (100)) decreased gradually during process of ball milling, which was 15. 5nm after ball milling for an hour and reduced to 6nm milled for 71 hours. The macrostress of the powders (Co(100)) increased gradually during the process. The microstress(Co(100)) of the powders increased in the early 31 hours and decreased gradually at the rest time. The microstress(Co(002)) reached the maximum at 59h and then decreased. Relationship of microstress of Co100-x(La2O3) x powders (Co (100)) with the content of La2O3 was that, when x≤4, the microstress of the powders increased with increase of the content of La2O3 and reached the maximum when x=5, then decreased appreciably. It was observed that for the powders of Co100-x(La2O3x mill ed for 63 hours, when x≤4, the samples presented the X-ray diffraction peaks of F. C. C structure of CoO, while the peaks disappeared when x≥5. When x≤4 the samples presentthe X-ray diffraction peaks of F. C. C structure of CoO, while the peaks disappeared when x^5. It was showed that some content of La^Os can inhibit from the oxidation of cobalt during ball milling process. It was believed that during the ball milling, there were rich content of LaA in the grain boundary regions and surfaces of the powders of Coioo,(La203)i when x^5, and the bigger size of La3+ induced cobalt lattice deformation which blocked the entry of oxygen into cobalt lattice and so inhibited oxidation of cobalt; but when x^4, the lattice deformation which La3+ caused was too slight to block the entry of oxygen into cobalt lattice., which caused oxidation of cobalt It was showed that crystal size of Co94(Ce02)6 powders (Co (100)) decreased gradually during the process of ball milling, which was 17nm after ball milling for an hour and reduced to 7nm milled for 71 hours. The macrostress of the powders(Co(100)) increased gradually during the process. The microstress of the powders (Co (100)) increased in the early 55h and decreased gradually at the rest time. The microstress(Co(002)) reached the maximum at 59h and then decreased. Relationship of microstress of Coi00-X (CeO2), powders (Co (100)) with the content of CeO2 was, when x^7, the microstress of the powders increased with increase of the content of CeO2 and reached the maximum when x=7, and then decreased rapidly. The microstress of the powders, when x=7, 8, was far bigger than thatof other contents of CeO2. It was observed that for the powders of Coioo-x(CeO2)? milled for 63 hours, when x=7, 8, the samples presented the X-ray diffraction peaks of F. C. C structure of CoO, while the peaks disappeared while other contents of CeO2. It was showed that some content of rare earth oxides CeO2 can inhibit the oxidation of Co during ball milling. It was believed that during the ball milling, there were very rich content of CeO2 in cobalt grain boundary regions and surfaces of the powders when x=7, 8, the bigger size of Ce4+ induced cobalt lattice deformation which blocked the entry of oxygen into cobalt lattice and so inhibited oxidation of cobalt; but when other contents of CeO2, the cobalt lattice deformation which Ce4+ caused was too slight to block the entry of oxygen into cobalt lattice., which caused oxidation of cobalt.The mechanism that rare earth and its oxide can improve oxidation resistance of metals is still controversial. Differently, we find that some content of rare earth oxides (La203, CeO2) can inhibit from the oxidation of cobalt during ball milling process, we believe that during the ball milling, there are very rich contents of rare earth oxides (La203, CeO2) in grain boundary regions and surfaces of the powders, the bigger size of rare earth oxides (La203, CeO2) induce cobalt lattice deformation which block the entry of oxygen into cobalt lattice and so inhibited oxidation of cobalt; but when other

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