摘要
甲烷与二氧化碳重整制取低碳氢比(CO／H2比为1)的合成气,为费托合成提供理想的原料。同时CO2是重整反应的反应物,这不但在一定程度上减少了温室气体的排放,而且能够将CO2作为一种可以利用的碳源。因此该反应对于节约资源和发展低碳循环经济都具有重要的意义,同时还能缓解日益严重的环境问题。虽然甲烷与二氧化碳重整具有环境和经济上的诸多优势,但重整反应始终没有工业化,其主要原因为贵金属成本高和镍基催化剂积碳问题严重。
本文以金属碳化钼以及镍改性碳化钼为催化剂,对其甲烷与二氧化碳重整反应进行研究,研究工作主要有如下三方面：
1.采用程序升温碳化方法以MoO3为前躯体碳化制备Mo2C,采用XRD对其进行表征分析,考察碳化温度、Mo2C／Al2O3、以及等离子体放电对Mo2C催化剂催化CH4-CO2重整反应活性以及稳定性的影响。结果表明常压下高温低空速有利于Mo2C的稳定,等离子体放电对其活性影响很小,催化剂活性失活主要原因是Mo2C氧化失活而不是积碳。
2.采用共沉淀的方法制备NiMoOx前躯体,并采用程序升温法碳化制备Ni-Mo2C,考察镍的加入对碳化物碳化温度的影响。同时考察了不同Ni／Mo比,空速、不同合成温度对催化活性的影响,以及常压高温条件下Ni-Mo2C催化剂的稳定性。结果表明在常压下Ni-Mo2C催化剂具有较高的稳定性,在实验的36小时内活性相对稳定,CH4转化率达到85%以上。
3.用程序升温还原(CH4-TPR)和程序升温氧化(CO2-TPO)等技术对催化剂的微观反应机制进行研究,结果表明：镍的加入有利于碳化物的合成,同时促进甲烷裂解,从而有利于碳化物在常压条件下的氧化-碳化循环的建立。
The synthesis gas with a low hydrocarbon ration produced by the reforming of methane with carbon dioxide provides an ideal raw material for Fischer-Tropsch synthesis. While CO2 being a reactant, this not only reduce greenhouse gas emissions to some extent, but also make CO2 as an available carbon source. So this reforming reaction is significant on resource conservation and the development of low-carbon economy when easing the increasingly serious environmental problems. Although the reforming has many environmental and economic advantages, this still has not been industrialized, which mainly due to the high cost of precious metals and the serious problem of nickel-based catalysts coking. In this paper, metal molybdenum carbide and nickel modified molybdenum carbide catalyst were prepared and their catalytic performances were investigated for CH4-CO2 reforming reaction in laboratory scale. The main content was described from three aspects as follows:
1. Mo2C was prepared from the precursor MoO3 by temperature programmed carbonization method and characterized by XRD analysis. Carbonization temperature, Mo2C/Al2O3, and the impact from plasma discharge on activity and stability of CH4-CO2 reforming reaction with Mo2C being the catalyst were also studied. The results show that low-speed and high temperature at atmospheric pressure are conducive to Mo2C stability, and plasma discharge has little effect on its activity. The main reason of catalyst deactivation is Mo2C oxidation inactivation rather than coke.
2. NiMoOx and Ni-Mo2C were prepared by co-precipitation and temperature programmed carbonization method respectively. The effect of added nickel on carburized temperature of the carbide was studied. We also investigated the impact of different Ni/Mo ratio, GHSV, synthesis temperature on the catalytic activity and stability of Ni-Mo2C catalyst at atmospheric pressure and high temperature. The results show that under atmospheric pressure Ni-Mo2C catalyst has high stability, and within the experimental 36 hours the activity is relatively stable, the conversion rate of CH4 can reach to 85%.
3. The reaction mechanism was studied by temperature programmed reduction (CH4-TPR) and temperature programmed oxidation (CO2-TPO). The results show that the addition of nickel is facilitated for carbide synthesis and promoting methane decomposition, therefore it is conducive to the stability of molybdenum carbide at atmospheric pressure.
引文
[1]李文钊.天然气催化转化新进展.石油与天然气化工,1998,27(1)：1-3
[2]李正清,陶鹏万.现代化工.2000,20(3),5
[3]Bach W, Fiebig S, China's Key Role in Climate Protection, Energy,1998,23 (4):253-270, Berlin:SPringer-Verlag,1993,321-337.
[4]张坤民.21世纪中国环境面临的挑战与决策[J].环境保护,1999,1：33-35.
[5]黄伟传,詹锋.富集CO2油田气生产食品级CO2.天然气化工,1991,16(4)：25-27
[6]肖亚平.二氧化碳温室效应对策[J].现代化工,1995,(9)：34-36
[7]陈吉祥,王日杰,张继炎.甲烷与二氧化碳重整制取合成气研究进展[J].天然气化工.2003.28：32-37
[8]阎子峰,宋林花.天然气有效利用途径回顾[J1.石油大学学报(自然科学版),1997,21(1)：103-105
[9]化工部天然气化工信息站.国内碳一化学进展一甲烷化学及合成气化学[J].天然气化工,1995,20(3)：44-49
[10]黄海燕,沈志虹.天然气转化制合成气的研究[J].石油与天然气化工.2000,29(6)276-279
[11]HooK J. A. van. Methane steam reforming. Catal. Rev. Sci. Eng,1980,21 (1):1.
[12]Lang J.Z.Phy.Chem,1888,2:161.
[13]Neumann B and Jacob K. Z. Elektrochem.1924,30:557
[14]Bymc Jr. P. J, Gohr R. J, Haslam R. T. Recent progress in hydrogenation of petroleum. Ind. Eng. Chem,1932,24:1129.
[15]Kochloffl K, Ertl G, Knozinger H, et al. Handbook of Heterogeneous Catalysis, Vol.4, P.1819, wiley,1997.
[16]毕先钧,洪品杰,戴树珊.甲烷部分氧化制合成气的研究[J].分子催化,1998,12(5)：342-348
[17]路勇,沈师孔.甲烷部分催化氧化制合成气研究新进展[J].石油与天然气化工,1997,26(1)：6-14
[18]严前古,于作龙,远松月.甲烷部分氧化制合成气研究进展[J].石油与天然气化工,1997,26(3)：145-151
[19]陶家林,李庆,康星武.甲烷氧化制合成气300m3／d规模扩试技术开发[J].天然气化工，2001,26(1)：27-30
[20]Huff M, Torniainen P. W, Schmidt L. D. Partial oxidation of alkanes over noble metal coated monoliths. Catal Today,1994,21 (1):113-128.
[21]Pena M. A, Gomez J. P, Fierro J. L. G. New catalytic routes for syngas and hydrogen production. Appl. Catal. A,1996,144:7-57.
[22]Rostrup-Nielsen J. R. Production of synthesis Gas. Catal. Today,1993,18:305-324.
[23]Bradford M. C.J, Annice M. A. C02 reforming of CH4 over supported Pt catalysts.J Catal,1998,173(1):157-171
[24]Ashcrift A. T, Cheetham A. K, Green M. L. H. Partial oxidation of methan synthesis gas using carbon dioxide. Nature,1991,52:225-226
[25]吴越.气化和气体合成反应的热力学.中国工业出版社,北京,1965
[26]许峥,张继炎,张鎏.甲烷二氧化碳反应热力学研究.石油化工,1977
[27]Wang S. B, Lu G. Q, Millar Graeme J. Carbon dioxide reforming of methane to produce synthesis gas over metal-supported catalyst:state of art. Energy & Fuels,1996, 10:896-904.
[28]Gadalla A. M, Bower B. The role of catalyst support on the aetivity of nickel for reforming methane with CO2. Chem. Eng. Sci,1988,43(11):3049-3062.
[29]Portugal U. L, Santos A. C. S. F. and Bueno J. M. C. CO2 reforming of CH4 over Rh-containing catalysts. J Mol Catal a-Chem,2002,184:311-322.
[30]Yang M and Papp H. CO2 reforming of methane to syngas over highly active and stable Pt/MgO catalysts. Catal Today,2006,115:199-204.
[31]Verykios X. E. Mechanistic aspects of the reaction of C02 reforming of methane over Rh/Al2O3 catalyst. Appl. Catal. A,2003,255:101-111.
[32]Matsui N.0, Anzai K, Akamatsu N, et al. Reaction mechanism of carbon dioxide reforming of methane with Ru-loaded lanthanum oxide catalyst. Appl. Catal. A,1999, 179:247-256.
[33]Wei J. M and I glesia E. Isotopic and kinetic assessment of the mechanism of methane reforming and decomposition reactions on supported iridium catalysts. Phys. Chem. Chem. Phys,2004,6(13):3754-3759.
[34]Stagg-Williams S. M, Noronha F. B, et al. CO2 reforming of CH4 over Pt/ZrO2 catalysts promoted with La and Ce oxides. J Catal.2000,194:240-249.
[35]Hei M. J, Chen H. B, Yi J, et al. CO2 reforming of methane on transition metal surfaces. Surf Sci,1998,417:82-96
[36]Halliche D, Bouarab R, Cherif i 0, Bettahar M. M. Carbon dioxide reforming of methane on modified Ni/α-Al2O3 catalysts. Catal Today,1996,29:373-377
[37]Bradford M. C. J and Vannice M. A. Catalytic reforming of methane with carbon dioxide over nickel catalysts I. Catalyst characterization and activity. Appl. Catal. A, 1996,142:73-96
[38]Zhang Z. L and Verykios X.E. Mechanistic aspects of carbon dioxide reforming of methane to synthesis gas over Ni catalysts. Catal Lett,1996,38:175-179.
[39]Chen Y. G., Tomishige K. and Fujimoto K. Formation and characteristic properties of carbonaceous species on nickel-magnesia solid solution catalysts during CH4-CO2 reforming reaction. Appl. Catal. A,1997,161:L11-L17
[40]THoriuehi Osaki, Tatsuro Horiuchi, Kenzi Suzuki TSuuzki, et al. Catalyst performance of Mo2S and WS2 of the CO2 reforming of CH4 suppression of carbon deposition. Appl. Catal. A,1997,155(2):229-238
[41]Krylov O.V, Mamedov A. K, MiZrabkova S. R. Inertaction of carbon dioxide with methane on oxide catalysts. Catal Today,1998,42(3):211-215
[42]Claridge J.B, York A. P. E, Brungs A. J, et al. New Catalysts for the Conversion of Methane to Synthesis Gas:Molybdenum and Tungsten Carbide. J Catal, 1998,180:85-100
[43]Terribile D, Trovarelli A, Primavera A, Dolcetti G, et al. Catalytic combustion of hydrocarbons with Mn and Cu-doped ceria-zirconia solid solutions. Catal Today,1999, 47(1-4):133-140.
[44]Li X. S, Chang J. S, Park S. E. Carbon as an intermediate during the carbon dioxide reforming of methane over zirconia-supported high nickel loading catalysts. Chem. Lett.1999,10:1099-1100.
[45]Li X. S, Chang J. S, Tian M. Y, Park and S. E. CO2 reforming of methane over modified Ni/ZrO2 catalysts. Applied Organometallic Chemistry 2001,15(2):109-112.
[46]Roh H. S, Potdar H. S, Jun K. W. Carbon dioxide reforming of methane over coprecipitated Ni-CeO2, Ni-ZrO2 and Ni-Ce-Zr02 catalysts. Catal Today 2004,93-95: 39-44.
[47]Trovarelli A, deLeitenburg C, Dolcetti G. Design better cerium-based oxidation catalysts. Chem tech 1997,27(6):32-37.
[48]Rossignol S, Gerard F, Duprez D. Effect of the preparation method on the properties of zirconia-ceria materials. J. Mater. Chem.1999,9(7):1615-1620
[49]Bradford M. C. J. and Vannice M.A. Catal Rev. Sci.Eng,1999 41(1):1-42
[50]严洪杰,杨骏英,周德幢.CeO2对Ni／γ-Al2O3,Pt／γ-Al2O3中Ni,Pt分散度的影响.天然气化工1992,17(5),26.
[51]宋一兵,赵修华,纪红兵,林维明.CH4、CO2与O2催化氧化重整制合成气的研究—催化剂中Ce02的作用及影响.天然气化工,1998,23(4)：12-14.
[52]Wang S. B., Lu G. Q. M. Effects of promoters on catalytic activity and carbon
deposition of Ni/γ-Al2O3 catalysts in CO2 reforming of CH4. J. Chem. Technol. Biotechnol. 2000,75(7):589-595.
[53]Wang S. B, Lu G. Q. Role of CeO2 in Ni/CeO2-Al2O3 catalysts for carbon dioxide reforming of methane. Appl. Catal. B,1998,19(3-4):267-277.
[54]Damyanova S, Bueno J.M. C. Effect of CeO2 loading on the surface and catalytic behaviors of CeO2-Al2O3-supported Pt catalysts. Appl. Catal. A,2003,253(1):135-150.
[55]许峥,李玉敏,张继炎,张鎏,何菲.甲烷二氧化碳重整制合成气的镍基催化剂性能Ⅱ.碱性助剂的作用.催化学报1997,18(5)：364-367.
[56]Martinez R, Romero E, Guimon C, Bilbao R. CO2 reforming of methane over coprecipitated Ni-Al catalysts modified with lanthanum. Appl. Catal. A,2004,274 (1-2):139-149
[57]Miao Q, Xiong G. X, Li X. S, et al. Acid-baseproperties and the directions of oxidative transformation of methane over nickel-based catalysts. Catal Lett.1996, 41(3-4):165-169.
[58]Chang J. S, Park S. E, Yoo J. W, Park J. N. Catalytic behavior of supported KNiCa catalyst and mechanistic consideration for carbon dioxide reforming of methane. J Catal,2000,195(1):1-11.
[59]Osaki T, Mori T. Role of potassium in carbon-free CO2 reforming of methane on K-promoted Ni/Al2O3 catalysts. J Catal,2001,204(1):89-97.
[60]Juan-Juan J, Roman-Martinez M. C. Catalytic activity and characterization of Ni/Al2O3 and NiK/Al2O3 catalysts for CO2 methane reforming. Appl. Catal. A,2004, 264 (2):169-174.
[61]Stagg S. M, Romeo E, Padro C, Resasco D. E. Effect of promotion with Sn on supported Pt catalysts for CO2 reforming of CH4. J Catal,1998,178(1):137-145.
[62]Choi J. S, Moon K. I, et al. Stable carbon dioxide reforming of methane over modified Ni/Al2O3 catalysts. Catal Lett,1998,52(1-2):43-47.
[63]Nichio N, CasellaM. L, Santori G. F, Ponzi E. N. Stability promotion of Ni/alpha-Al2O3 catalysts by tin added via surface organometallic chemistry on metals-Application in methane reforming processes. Catal Today,2000,62(2-3):231-240.
[64]Hou Z. Y, Yokota 0, Tanaka T, Yashima T. Surface properties of a coke-free Sn doped nickel catalyst for the CO2reforming of methane. Appl. Surf. Sci,2004, 233(1-4):58-68.
[65]Levy R. B and Boudart M. Platinum-Like Behavior of Tungsten Carbide in Surface Catalysis. Science,1973,181:547-549
[66]Wu H and Chen J. Surface Chemistry of Transition Metal Carbides. Chem Rev,2005, 105:185-212
[67]Oyama S. T. Preparation and catalytic properties of transition metal carbides and nitrides. Catal Today,1992,15:179-200
[68]幺志伟.过渡金属氮化物、碳化物和磷化物的制备、表征及NO解离和还原性能[D].辽宁：大连理工大学化工学院,2009.
[69]Leclercq L, Imura K, Yoshida S, et al. Preparation of catalysis Ⅱ. Delmon B, Grange P, Jacobs P et al. Eds, P.627, Elsevier, Amsterdam,1979.
[70]Hyeon T, Fang M, Suslick K. S. Nanostructure molybdenum carbide:sonochemical synthesis and catalytic properties. J. Am. Chem. Soc,1996,118:5492-5493.
[71]Li S, Lee J. S, Hyeon T, et al. Catalytic hydrodenitrogenation of indole over molybdenum nitrides and carbides with defferent structure. Appl. Catal. A,1999, 184:1-9.
[72]Volpe L, Boudart M. Compounds of molybdenum and tungsten with high specific surface area. I. Nitrides. J Solid State Chem,1985,59:332-347.
[73]Volpe L, Boudart M. Compounds of molybdenum and tungsten with high specific surface area. Ⅱ. Carbides. J Solid State Chem,1985,59:348-356.
[74]Mitao T, Shishikuka I, Mjatsuoka M, et al. CVD synthesis of alumina-supported molybdenum carbide catalyst, Chem. Lett,1996:561-562
[75]Subramanya H. P, Hegde M. S, Vasathacharya H. Y, et al. Synthesis of TiN, VN and CrN from ammonolysis of TiS2, VS2 and Cr2S3. J Solid State Chem,1997,134:120-127.
[76]Zheng D, Hampden-Smith M. J. Room-temperature synthesis of molybdenum and tungsten carbides Mo2C and W2C, via chemical reduction methods. Chem. Mater,1992,4:968-970.
[77]Koyamo T, Lee C. H, Fukunaga T, et al. Formation of iron nitrides by mechanical alloying in ammonia atmosphere. Mater. Sci. Forum,1992,88-90:809-816.
[78]Kaczmarek W. A, Ninham B. W, Onsyzkiewicz I, Synthesis of Fe3N by mechano-chemical reactions between iron and organic Hx(CN)6 ring compounds. J Mater Sci,1995, 30(21):5514-5521.
[79]Ronsheim P, Mazza A, Christensen A. N, et al. Thermal plasma synthesis of transition metal nitrides and alloys. Plasma. Chem. Plasma. Process,1981,1(2):135-147.
[80]Wu J. D, Wu C. Z, Song Z. M, et al. Preparation of molybdenum nitrides by laser-promoted nitridation reaction. Thin Solid Films,1997,311(1-2):62-66
[81]Sehested J, Jacobsen C. J. H, Rokni S, et al. Activity and stability of molybdenum carbide as a catalyst for CO2 reforming. J Catal,2001,201:206-212
[82]Schlatter J. C, Oyama S. T, Metcalfe J. E, et al. Catalytic behavior of selected transition metal carbides, nitrides, and borides in the hydrodenitrogenation of quinoline. Ind. Eng. Chem. Res,1988,27:1648-1653
[83]Aegerter P. A, Quigley W. C, Simpson G. J, et al. Thiophene hydrodesul furization over alumina-supported molybdenum carbide and nitride catalysts:adsorption sites, catalytic activities, and nature of the active surface. J Catal,1996,164:109-121
[84]Gallo P. D, Meunier F, et al. Selective n-butane isomerization over high specific surface area MoO3-carbon-modified catalyst. Ind Eng Chem Res,1997,36:4166-4175
[85]Hemming F, Wehrer P, Katrib A, et al. Reactivity of hexanes (2MP, MCP and CH) on W, W2C and WC powders. Part Ⅱ. Approach to the reaction mechanisms using concepts of organometallic chemistry. J Mol. Catal. A,1997,124:39-56
[86]Nagai M, Kurakami T, Omi S. Activity of carbided molybdena-alumina for CO2 hydrogenation. Catal Today,1998,45:235-239
[87]Ranhotra G. S, Bell A. T, Reimer J. A. Molybdenum carbide catalysts:I. Synthesis of unsupported powders J Catal,1987,108:40-49
[88]Hwu H. H, Chen J. G. Potential application of tungsten carbides as electrocatalysts: IV. Reactions of methanol and water on closed-packed carbide surfaces. J Phys. Chem.B,2003,107:2029-2039
[89]朱全力,杨建,季生福等.过渡金属碳化物的研究进展.化学进展.2004,16(3)382-385
[90]Rostrup-Nielsen J. R, in:J. R. Anderson, M. Boudart (Eds.). Catalysis Science and Technology, vol.5, Springer, Berlin,1984, p. 1.M
[91]Xiao T. C, Hanif A, York Andrew P. E, et al. Study on preparation of high surface area tungsten carbides and phase transition during the carburization. Phys. Chem. Chem. Phys,2002,4:4549-4554.
[92]Darujati A. R. S, LaMont D. C and Thomson W. J. Oxidation stability of Mo2C catalysts under fuel reforming conditions. Appl. Catal. A,2003,253:397-407.
[93]Zhu Q. L, Zhang B, Yang J, et al. The promotion of nickel to Mo2C/Al2O3 catalyst for the partial oxidation of methane to syngas. New J Chem,2003,27:1633-1638.
[94]Zhu Q. L, Zhang B, Zhao J, et al. The effect of secondary metal on Mo2C/Al2O3 catalyst for the partial oxidation of methane to syngas. J Mol Catal a-Chem,2004, 213:199-205.
[95]Naito S, Tsuji M and Miyao T. Mechanistic difference of the CO2 reforming of CH4 over unsupported and zirconia supported molybdenum carbide catalysts. Catal Today, 2002,77:161-165.
[96]Sehested J, Jacobsen C. J. H, Rokni S, et al. Activity and stability of molybdenum carbide as a catalyst for CO2 reforming. J Catal,2001,201:206-212.
[97]LaMont D. C. and Thomson W. J. Dry reforming kinetics over a bulk molybdenum carbide catalyst. Chem Eng Sci,2005,60:3553-3559.
[98]Tsuji M, Miyao T, Naito S. Remarkable support effect of ZrO2 upon the CO2 reforming of CH4 over supported molybdenum carbide catalysts. Catal Lett,2000,69:195-198.
[99]Lyer M. V, Dadyburjor D. B. Top Catal,2004,29:197
[100]Lamont D. C, A. Gilligan J, Darujati A. R. S, et al. The effect of Mo2C synthesis and pretreatment on catalytic stability in oxidative reforming environments. Appl. Catal. A,2003,255:239-253.
[101]Darujati A. R. S, Thomson W. J. Stability of supported and promoted-molybdenum carbide catalysts in dry-methane reforming. Appl. Catal. A,2005,296:139-147.
[102]Nagai M, Zahidul A. M, Matauda K. Nano-structured nickel-molybdenum carbide catalyst for low-temperature water-gas shift reaction. Appl. Catal. A,2006, 313:137-145.
[103]Wang H, Wang A. Q, Wang X. D, et al. One-pot synthesized MoC imbedded in ordered mesoporous carbon as a catalyst for N2H4 decomposition. Chem. Commun, 2008:2565-2567.
[104]Wu W.C, Wu Z. L, Liang C.H, et al. In Situ FT-IR Spectroscopic Studies of CO Adsorption on Fresh Mo2C/Al2O3 Catalyst. J. Phys. Chem. B,2003,107:7088-7094
[105]Wu W, Wu Z, Liang C, et al. An IR study on the surface passivation of M02C/Al2O3 catalyst with 02, H20 and C02. Phys. Chem. Chem. Phys,2004,6:5603-5608
[106]Ji N, Zhang T, Zheng M, et al. Direct Catalytic Conversion of Cellulose into Ethylene Glycol Using Nickel-Promoted Tungsten Carbide Catalysts. Angewandte Chemie International Edition,2008,47:8510-851