利用恒温还原和程序升温还原技术研究了水分压对铁基费托合成催化剂还原路径、还原机理和表观活化能的影响.程序升温还原结果表明,水分压对催化剂的还原路径没有明显的影响,催化剂均首先由α-Fe_2O_3还原为Fe_3O_4,然后超顺磁态Fe_3O_4先还原为FeO,再还原为α-Fe,而顺磁态Fe_3O_4则直接还原为α-Fe.恒温还原结果表明,催化剂在2.5%H_2O-97.5%H_2气氛中还原时,还原过程达到平衡时的还原程度随还原温度的升高而增加.利用Hancock-Sharp方法分析了恒温还原过程的动力学模型.结果表明,还原温度较低时,催化剂在2.5%H_2O-97.5%H_2气氛中还原时受内扩散模型控制;还原温度较高时则受晶相形成与生长模型控制.利用Kissinger方法计算了还原过程的活化能,发现随着水分压的增加,表观活化能呈增大的趋势.水分压对Fe_3O_4还原为α-Fe过程的影响大于其对α-Fe_2O_3还原为Fe_3O_4过程的影响.
The effect of H_2O partial pressure on the reduction pathway, mechanism, and apparent activation energy of an iron-based Fischer-Tropsch catalyst was investigated by isothermal and temperature-programmed reduction (TPR). The TPR results indicated that the H_2O partial pressure had no obvious influence on the reduction pathway of the catalyst in H_2. α-Fe_2O_3 in the catalyst was first reduced to Fe_3O_4. The formed superparamagnetie Fe_3O_4 was reduced to a-Fe via FeO as an intermediate, while the formed paramagnetic Fe_3O_4 was reduced to α-Fe directly. The isothermal reduction of the catalyst showed that the reduction degree of the catalyst increased with the increase of reduction temperature when the reaction approached to equilibrium. The reduction mechanism analyzed based on the Hancock-Sharp method indicated that the reduction of the catalyst in 2.5%H_2O-97.5%H_2 at lower temperature was controlled by the inner diffusion model. However, at higher temperature the reduction process was controlled by the formation and growth of nuclei model. The apparent activation energy calculated based on the Kissinger method was increased with increasing H_2O partial pressure in H_2. The H_2O partial pressure had stronger influence on the reduction of Fe_3O_4 to α-Fe than that on the reduction of α-Fe_2O_3 to Fe_3O_4.
参考文献
| [1] | Dry M E .[J].Catalysis Today,2002,71:227. |
| [2] | de Smit, E.;Beale, A.M.;Nikitenko, S.;Weckhuysen, B.M. .Local and long range order in promoted iron-based Fischer-Tropsch catalysts: A combined in situ X-ray absorption spectroscopy/wide angle X-ray scattering study[J].Journal of Catalysis,2009(2):244-256. |
| [3] | Bukur DB.;Manne RK.;Lang XS.;Nowicki L. .ACTIVATION STUDIES WITH A PRECIPITATED IRON CATALYST FOR FISCHER-TROPSCH SYNTHESIS .2. REACTION STUDIES[J].Journal of Catalysis,1995(2):366-375. |
| [4] | 安霞,吴宝山,万海军,李廷真,陶智超,相宏伟,李永旺.浸渍钠对铁基催化剂F-T合成浆态床反应性能的影响[J].催化学报,2007(09):766-772. |
| [5] | 吴宝山,白亮,张志新,相宏伟,李永旺,易凡,徐斌富.不同沉淀剂制备的铁基催化剂对浆态床F-T合成反应的催化性能[J].催化学报,2005(05):371-376. |
| [6] | 沈俭一;林励吾;章素;梁东白 .[J].催化学报,1993,14(07) |
| [7] | 沈俭一;林励吾;Berry F J .[J].催化学报,1993,14(01) |
| [8] | Wang H;Yang Y;Wu B S;Xu J Ding M Y Wang H L Fan W H Xiang H W Li Y W .[J].Journal of Molecular Catalysis A:Chemical,2009,308:96. |
| [9] | Tiernan M J;Barnes P A;Parkes G M B .[J].Journal of Physical Chemistry B,2001,105:220. |
| [10] | Ning W S;Koizumi N;Chang H;Mochizuki T Itoh T Yamada M.[J].Applied Catalysis A:General,2006:312 35. |
| [11] | Botes FG .The Effects of Water and CO2 on the Reaction Kinetics in the Iron-Based Low-Temperature Fischer-Tropsch Synthesis: A Literature Review[J].Catalysis Reviews. Science and Engineering,2008(4):471-491. |
| [12] | Satterfield C N;Hanlon R T;Tung S E;Zou Z M Papaefthymiou G C .[J].Industrial and Engineering Chemistry:Product Research and Development,1986,25:407. |
| [13] | Wimmers O J;Arnoldy P;Moulijn J A .[J].Journal of Physical Chemistry,1986,90:1331. |
| [14] | Khawam A;Flanagan D R .[J].Journal of Physical Chemistry B,2006,110:17315. |
| [15] | 王洪,杨勇,吴宝山,许健,王虎林,定明月,相宏伟,李永旺.焙烧温度对费托合成铁基催化剂还原动力学的影响[J].催化学报,2009(11):1101-1108. |
| [16] | Hancock J D;Sharp J H .[J].Journal of the American Ceramic Society,1972,55:74. |
| [17] | Kissinger H E .[J].Analytical Chemistry,1957,29:1702. |
| [18] | K(u)ndig W;B(o)mmel H;Constabaris G;Lindquist R H .[J].Physical Review,1966,142:327. |
| [19] | Jin Y;Datye A K .[J].Journal of Catalysis,2000,196:8. |
| [20] | Kock A J H M;Fortuin H M;Geus J W .[J].Journal of Catalysis,1985,96:261. |
| [21] | 葛庆仁.气固反应动力学[M].北京:原子能出版社,1991:34. |
| [22] | Nabi G;Lu W K .[J].Industrial and Engineering Chemistry Fundamentals,1974,13:311. |
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