氫氣為燃料電池主要的能量來源，多採碳氫化合物蒸汽重組為主,其中又以甲醇產氫系統最為簡單，適用於移動式供氫。甲醇產氫常見的反應有甲醇蒸汽重組(SRM)、甲醇部分氧化(POM)與複合式甲醇蒸汽重組(OSRM)，其中SRM與OSRM反應產氫效率較高，CO選擇率低。
本實驗室過去產氫觸媒設計的研究以商業觸媒G66B(CuO/ZnO/Al2O3=30/60/10)成分為基礎，以共沉澱法製備不 同比例之CuO/ZnO/CeO2/ZrO2/Al2O3觸媒，進行SRM及OSRM反應，發現CeO2與Al2O3為負面影響，ZrO2則有不錯促進活性與增進穩定性的效果，但較高CuO負載量(大於30%)時ZrO2促進效果無法顯現，甚至有負面的效果，本研究固定CuO/ZnO/Al2O3觸媒中Al2O3含量為10 wt%，在不同CuO負載量(10~40 wt%)觸媒中引入不等量ZrO2取代部分ZnO，進行SRM及OSRM反應，藉以近一步探討ZrO2對CuO/ZnO/Al2O3觸媒的影響。研究發現ZrO2可提升觸媒的還原能力、分散性，也增進觸媒的穩定。DRFTIR分析發現ZrO2可增加甲醇吸附，適量添加可促進反應活性。觸媒中CuO/ZnO比值為影響觸媒活性的重要因素，CuO/ZnO比值小於0.8，ZrO2對觸媒活性有促進效果，如過量添加ZrO2取代ZnO，使CuO/ZnO比值大於0.8，減少 CuO/ZnO之間的交互周界，ZrO2的促進效果無法顯現，甚至對觸媒活性有負面影響。

Abstract
The proton exchange membrane fuel cells (PEMFC) usually use hydrogen as feed, and the methanol hydrogenation which is the most simply hydrogen production system therefore the system also apply to onboard equipment. The steam reforming of methanol (SRM) and oxidative steam reforming of methanol (OSRM) are two of the best hydrogen production of methanol reaction.
In our past research, commercial catalysts G66B (Nisson-Gridler) with weight ratio of 30/60/10 (CuO/ZnO/Al2O3) was used as a starting reference for designing CuO/ZnO/ZrO2/Al2O3 catalysts which were prepared by co-precipitation method for SRM and OSRM. We find out that the CeO2 and Al2O3 were negative to the catalyst activity, ZrO2 had excellent performance on catalytic activity and stability, nevertheless when high loading ZrO2 (above 30 wt %), the promotion of ZrO2 had disappeared. In this research, we fixed Al2O3 composition in the CuO/ZnO/ZrO2/Al2O3 catalyst as 10 wt%, and change the composition of rest of the species of catalyst, and introducing ZrO2 replace the partial ZnO in the catalyst test in SRM and OSRM reactions try to figure out the influence of ZrO2 in CuO/ZnO/Al2O3-based catalysts.
ZrO2 could improve the catalytic reducibility and the copper dispersion on catalyst and increase the stability of catalyst, in DRIFT we also note the obvious evidence that ZrO2 could increase the methanol adsorption on catalyst. The CuO/ZnO ratio is extremely important to the catalytic activity, when the ratio is above 0.8, introducing ZrO2 show no improvement ,when the ratio below 0.8, introducing ZrO2 improve the catalytic activity and the stability.

參考文獻
[1] P.H. Matter, D.J. Braden, U.S. Ozkan, Steam reforming of methanol to H2 over nonreduced Zr-containing CuO/ZnO catalysts, J. Catal. 223 (2004) 340－351.
[2] P.H. Matter, U.S. Ozkan, Effect of pretreatment conditions on Cu/Zn/Zr-based catalysts for the steam reforming of methanol to H2, J. Catal. 234 (2005) 463－475.
[3] D. Bianchi, T. Chafik, M. Khalfallah, S.J. Teichner, Intermediate species on zirconia supported methanol aerogel catalysts V. Adsorption of methanol, Appl. Catal. A: Gen. 123 (1995) 89－110.
[4] J. Agrell, H. Birgersson, M. Boutonnet, I. Melián-Cabrera, R.M. Navarro, J.L.G. Fierro, Production of hydrogen from methanol over Cu/ZnO catalysts promoted by ZrO2 and Al2O3, J. Catal. 219 (2003) 389－403.
[5] G. Fierro, M.L. Jacono, M. Inversi, P. Porta, F. Cioci, R. Lavecchia, Study of the reducibility of copper in CuO---ZnO catalysts by temperature-programmed reduction, Appl. Catal. A: Gen. 137 (1996)21
[6] T. Fujitani, J. Nakamura, The chemical modification seen in the Cu/ZnO methanol synthesis catalysts, Appl. Catal. A: Gen. 191 (2000) 111－129.
[7] S. Rabe, F. Vogel, A thermogravimetric study of the partial oxidation of methanol for hydrogen production over a Cu/ZnO/Al2O3 catalysts, Appl. Catal. B: Envi. 84 (2008) 827－834.
[8] M.M. Günter, T. Ressler, R.E. Jentoft, B. Bems, Redox behavior of copper oxide/zinc oxide catalysts in the steam reforming of methanol studied by in situ X-ray diffraction and absorption spectroscopy, J. Catal. 203 (2001) 133－149.
[9] S. Fukahori, H. Koga, T. Kitaoka, A. Tomoda, R. Suzuki, H. Wariishi, Hydrogen production from methanol using a SiC fiber-containing paper composite impregnated with Cu/ZnO catalyst, Appl. Catal. A: Gen. 310 (2006) 138－144.
[10] S. Velu, K. Suzuki, M.P. Kapoor, F. Ohashi, T. Osaki, Selective production of hydrogen for fuel cells via oxidative steam reforming of methanol over CuZnAl(Zr)-oxide catalysts, Appl. Catal. A: Gen. 213 (2001) 47－63.
[11] 黃罡，「甲醇蒸汽重組觸媒設計CuO/ZnO/CeO2/ZrO2/Al2O3」，國立中央大學，化學工程與材料工程研究所，碩士論文，民國97年。
[12] 張丞鈞，「甲醇氧化/蒸汽重組複合式反應觸媒之設計CuO/ZnO/CeO2/ZrO2/Al2O3」，國立中央大學，化學工程與材料工程研究所，碩士論文，民國98年。
[13] N. Takezawa , N. Iwasa, Steam reforming and dehydrogenation of methanol: Difference in the catalytic functions of copper and group VIII metals, Catalysis Today 36 (1997) 45-56
[14] H. Kobayashi, N. Takezawa, C. Minochi, Methanol-reforming reaction over copper-containing catalysts—The effects of anions and copper loading in the preparation of the catalysts by kneading method ,J. Catal. 69 (1981) 487
[15] R.O. Idem, N.N. Bakhshi, Ind. Eng. Chem. Res. 34 (1995) 1548.
[16] G.-C. Shen, S.-I. Fujita, S. Matsumoto, N. Takezawa, J. Mol, Steam reforming of methanol on binary Cu/ZnO catalysts: Effects of preparation condition upon precursors, surface structure and catalytic activity, Catal. A 124 (1997) 123.
[17] J.P. Breen, J.R.H. Ross, Methanol reforming for fuel-cell applications: development ofzirconia-containing Cu/Zn/Al catalysts, Catal. Today 51 (1999) 521-533.
[18] B.A. Peppley, J.C. Amphlett, L.M. Kearns, R.F. Mann, Methanol – steam reforming on Cu/ZnO/Al2O3. Part 1: the reaction network, Appl. Catal. A 179 (1999) 21-29.
[19] N. Takezawa, H. Kobayashi, A. Hirose, M. Shimokawabe and K. Takahashi, Steam reforming of methanol on copper-silica catalysts; effect of copper loading and calcination temperature on the reaction, Appl. Catal. 4 (1982) 127－134.
[20] I. Ritzkopf, S. Vukojevic, C. Weidenthaler, J.-D. Grunwaldt, F. Schu¨th, Decreased CO production in methanol steam reforming overCu/ZrO2 catalysts prepared by the microemulsion technique, Appl. Catal. A: Gen. 302 (2006) 215-223
[21] A. Szizybalski, F. Girgsdies, A. Rabis, Y. Wang, M. Niederberger, T.
Ressler, In situ investigations of structure–activity relationships of a Cu/ZrO2 catalyst for the steam reforming of methanol, J. Catal. 233 (2005) 297-307.
[22] H. Purnama, F. Girgsdies, T. Ressler, J.H. Schattka, R.A. Caruso, R.
Schomaecker, R. Schloegl, Catal. Lett. 94 (2004) 61.
[23] I. Ritzkopf, C. Kiener, S. Vukojevic, R. Brinkmann, H. Boennemann, F.
Schueth, Novel Cu/ZnO and Cu/ZrO2 catalysts for methanol synthesis and steam reforming, in: Proceedings of the DGMK-Conference Innovation in the Manufacture and Use of Hydrogen, DGMK Tagungsbericht 2 (2003) 49–56, ISSN: 1433-9013.
[24] J. Papavasiliou, G. Avgouropoulos, T. Ioannides, Effect of dopants on the performance of CuO–CeO2 catalysts in methanol steam reforming, Appl. Catal. B: Environ.69 (2007) 226.
[25] J. Papavasiliou, G. Avgouropoulos, T. Ioannides, Catal. Commun. 5, Production of hydrogen via combined steam reforming of methanol over CuO–CeO2 catalysts, Catal. Commun (2004) 231-235
[26] W. Shan, Z. Feng, Z. Li, J. Zhang,W. Shen, C. Li, Oxidative steam reforming of methanol on Ce0.9Cu0.1OY catalystsprepared by deposition – precipitation, coprecipitation, and Complexation – combustion methodsm J. Catal. 228 (2004) 206.
[27] J. Papavasiliou, G. Avgouropoulos, T. Ioannides, Catal. Commun. 6, Steam reforming of methanol over copper–manganese spinel oxide catalysts, Catal. Commun (2005) 497-501.
[28] H. Oguchi, T. Nishiguchi, T. Matsumoto, H. Kanai, K. Utani, Y. Matsumura,S. Imamura, Steam reforming of methanol over Cu/CeO2/ZrO2 catalysts, Appl. Catal. A: Gen. 281 (2005) 69-73.
[29] B. Lindstro¨m, J. Agrell, L.J. Pettersson, Chem. Eng. J. 93 (2003) 91
[30] J.B. Wang, C.-H. Li, T.J. Huang, A comparison of oxygen-vacancy effect on activity behaviors of carbon dioxide and steam reforming of methane over supported nickel catalysts, Catal. Lett. 103 (3/4) (2005) 239–247
[31] G.C. Chinchen, K.C. Waugh, The activity and state of the copper surface in methanol synthesis catalysts, Appl. Catal. 25 (1986) 101-107.
[32] K. Klier , Methanol Synthesis, Adv. Catal. 31 (1982) 243-313.
[33] R. Burch, S.E. Golunski, M.S. Spencer, J. Chem. Soc.,Faraday Trans. 86 (1990) 2683.
[34] N.-Y. Topsøe, H. Topsøe, On the nature of surface structural changes in Cu/ZnO methanol synthesis catalysts, Top. Catal. 8 (1999) 267-270.
[35] S. Velu, K. Suzuki, M. Okazaki, M.P. Kapoor, T. Osaki, F. Ohashi, Oxidative steam reforming of methanol over CuZnAl(Zr)-oxide catalysts for the selective production of hydrogen for fuel cells: catalyst characterization and performance evaluation, J.Catal.194(2000) 373-384.
[36] B. Lindstro¨m, L.J. Pettersson, P.G. Menon, Activity and characterization of Cu/Zn, Cu/Cr and Cu/Zr on γ-alumina for methanol reforming for fuel cell vehicles, Appl. Catal. A: Gen. 234 (2002) 111-125.
[37] E.D. Batyrev, J.C. van den Heuvel, J. Beckers, W.P.A. Jansen, H.L. Castricum, The effect of the reduction temperature on the structure of Cu/ZnO/SiO2 catalysts for methanol synthesis, J. Catal. 229 (2005) 136-143.
[38] J.P. Breen, F.C. Meunier, J.R.H. Ross, Mechanistic aspects of the steam reforming of methanol over a CuO/ZnO/ZrO2/Al2O3 catalysts, Chem. Commun. (1999) 2247－2248.
[39] T. Shishido, Y. Yamamoto, H. Morioka, K. Takaki, K. Takehira, Active Cu/ZnO and Cu/ZnO/Al2O3 catalysts prepared by homogeneous precipitation method in steam reforming of methanol,Appl. Catal. A: Gen. 263 (2004) 249.
[40] T. Shishido, M. Yamamoto, D. Li, Y. Tian, H. Morioka, M. Honda, T.
Sano, K. Takehira, Water-gas shift reaction over Cu/ZnO and Cu/ZnO/Al2O3 catalysts prepared by homogeneous precipitation, Appl. Catal. A: Gen. 303 (2006) 62-71.
[41] J.-P. Shen, C. Song, Catal. Today 77 (2002) 89.
P75 – 22,038
[42] M. Turco, G. Bagnasco, U. Costantino, F. Marmottini, T. Montanari, G. Ramis, G. Busca, Production of hydrogen from oxidative steam reforming of methanol II. Catalytic activity and reaction mechanism on Cu/ZnO/Al2O3 hydrotalcite-derived catlaysts, J. Catal. 228 (2004) 56-65.
[43] H.G. El-Shobaky, M. Mokhtar, G.A. El-Shobaky, Physicochemical surface and catalytic properties of CuO–ZnO/Al2O3 system, Appl. Catal. A 180 (1999) 335-344.
[44] J.-L. Li, T. Inui, Characterization of precursors of methanol synthesis catalysts, copper/zinc/aluminum oxides, precipitated at different pHs and temperatures , Appl. Catal. A 137 (1996) 105-117.
[45] L. Alejo, R. Lago, M.A. Peña, J.L.G. Fierro, Partial oxidation of methanol to produce hydrogen over Cu---Zn-based catalysts, Appl. Catal. A 162 (1997) 281-297.
[46] S. Velu, K. Suzuki, T. Osaki, Catal. Lett. 62 (1999) 159.
[47] J.-L. Li, X.-G. Zhang, T. Inui, Appl. Catal. A 147 (1996) 23.
[48] Y. Zhang, Q. Sun, J. Deng, D. Wu, S. Chen, A high activity Cu/ZnO/Al2O3 catalyst for methanol synthesis: Preparation and catalytic properties, Appl. Catal. A 158 (1997) 105-120.
[49] Y. Ma, Q. Sun, D. Wu, W.-H. Fan, Y.-L. Zhang, J.-F. Deng, A practical approach for the preparation of high activity Cu/ZnO/ZrO2 catalyst for methanol synthesis from CO2 hydrogenation, Appl. Catal. A 171 (1998) 45-55.
[50] Y. Ma, Q. Sun, D. Wu, W.-H. Fan, J.-F. Deng, A gel-oxalate co-precipitation process for preparation of Cu/ZnO/Al2O3 ultrafine catalyst for methanol synthesis from CO2+H2: (II) effect of various calcination conditions, Appl. Catal.A 177 (1999) 177-184.
[51] W. Ning, H. Shen, H. Liu, Appl, Study of the effect of preparation method on CuO-ZnO-Al2O3 catalyst, Catal. A 211 (2001) 153.
[52] M.A. Larrubia Vargas ,G. Busca, U. Costantino, An IR study of methanol steam reforming over ex-hydrotalcite Cu–Zn–Al catalysts, Catalysis A: Chemical 266 (2007) 188–197
[53] S. Patel, K.K. Pant, Kinetic modeling of oxidative steam reforming of methanol over Cu/ZnO/CeO2/Al2O3 catalysts, Appl. Catal. A: Gen. 356 (2009) 189－200.
[53] E. Santacesaria, S. Carrá, Cinetica dello steam reforming del metanolo, Riv. Combust. 32 (1978) 227－232.
[54] E. Santacesaria, S. Carrá, Cinetica dello steam reforming del metanolo, Riv. Combust. 32 (1978) 227－232.
[55] J.C. Amphlett, M.J. Evans, R.F. Mann, R.D. Weir, Hydrogen production by the catalytic steam reforming of methanol. Part 2: Kinetics of methanol decomposition using Girdler G66B catalyst, Can. J. Chem. 63 (1985) 605－611.
[55] J.C. Amphlett, M.J. Evans, R.F. Mann, R.D. Weir, Hydrogen production by the catalytic steam reforming of methanol. Part 3: Kinetics of methanol decomposition using Girdler C18HC catalyst, Can. J. Chem. 66 (1988) 950－956.
[56] A.J. Marchi a J.L.G. Fierro b j. Santamaria c A. Monz6n c.,i, Dehydrogenation of isopropylic alcohol on a Cu/SiO2 catalyst: a study of the activity evolution and reactivation of the catalyst, Appl. Catal. A: Gen. 142 (1996) 357－386.
[57] A.P. Meyer, J.A.S. Bett, G. Vartanian, R.A. Sederquist, Parametric analysis of 1.5 kW methanol-fuel cell power plant designs, US Army Technical Report DAAK70-77-C-0195, 1978.
[58] R. Dümpelmann, Kinetische Untersuchungen des Methanol reforming und der Wassergaskonvertierungsreaktion in einem konsentrationgeregelten Kreislaufreaktor, Ph.D. Dissertation, Eidgenössischen Technischen Hochschule, Zürich, 1992.
[59] C.J. Jiang, D.L. Trimm, M.S. Wainwright, N.W. Cant, Kinetic study of steam reforming of methanol of copper-based catalysts, Appl. Catal. A: Gen. 93 (1993) 245－255.
[60] J.C. Amphlett, R.F. Mann, B.A. Peppley, The steam-reforming of methanol: mechanism and kinetics compared to the methanol synthesis process, in: H.E. Curry-Hyde, R.F. Howe (Eds.), Studies in Surface Science and Catalysis, vol. 81, Elsevier, Amsterdam, 1994, pp. 409-412, ISBN 0-444-89535-3.
[61] G. Liu, D. Willcox, M. Garland, and H. H. Kung, The role of CO2 in methanol synthesis on Cu-Zn oxide: An isotope labeling study, J. Catal. 96 (1985) 251－260.
[62] G.C. Chinchen, P.J. Denny, D.G. Parker, M.S. Spencer, and D.A. Whan, Mechanism of methanol synthesis from CO2/CO/H2 mixtures over copper/zinc oxide/alumina catalysts: Use of 14C-labelled reactions, Appl. Catal. 30 (1987) 333.
[63] N.E. Vanderborgh, B.E. Goodby, T.E. Springer, Oxygen exchange reactions during methanol steam reforming, in: Proceedings of the 32nd International Power Sources Symposium, 1986, pp. 623－628.
[64] K.C. Waugh, Methanol synthesis”, Catalysis Today 15 (1992) 51－75.
[65] J.K. Lee, J.B. Ko, D.H. Kim, Methanol steam reforming over Cu/ZnO/Al2O3 catalyst: kinetics and effectiveness factor”, Appl. Catal. A: Gen. 278 (2004) 25－35.
[66] H. Purnama, T. Ressler, R.E. Jentoft, H. Soerijanto, R. Schlögl, R. Schomäcker, CO formation/selectivity for steam reforming of methanol with a commercial CuO/ZnO/Al2O3 catalyst, Appl. Catal. A: Gen. 259 (2004) 83－94.
[67] M. Bowker, R.A. Hadden, H. Houghton, J.N.K. Hyland, K.C. Waugh, The mechanism of methanol synthesis on copper/zinc oxide/alumina catalysts, J. Catal. 109 (1988) 263－273.
[68] S.G. Neophytides, A.J. Marchi, G.F. Froment, “Methanol synthesis by means of diffuse reflectance infrared Fourier transform and temperature-programmed reaction spectroscopy, Appl. Catal. A: 86 (1992) 45－64.
[69] I.E.Wachs, R.J. Madix, The selective oxidation of CH3OH to H2CO on a copper (110) catalyst, J. Catal. 53 (1978) 208－227
[70] G.J. Millar, C.H. Rochester, K.C. Waugh, Infrared study of methyl formate and formaldehyde adsorption on reduced and oxidised silica-supported copper catalysts, J. Chem. Soc., Faraday Trans. 87(17) (1991) 2785－2793.
[71] B.A. Peppley, J.C. Amphlett, L.M. Kearns, R.F. Mann, Methanol steam reforming on Cu/ZnO/Al2O3 catalysts. Part 2. A comprehensive kinetic model, Appl. Catal. A: Gen. 179 (1999) 31－49.
[72] J. Skrzypek, J. Sloczynski, S. Ledakowicz, Methanol synthesis, ISBN 83-01-11490-8, Polish Scientific Publishers, Warsaw, 1994.
[73] J. Nakamura, I. Nakamura, T. Uchijima, Y. Kanai, T. Watanabe, M. Saito, T. Fujitani, A surface science investigation of methanol synthesis over a Zn-deposited polycrystalline Cu surface, J. Catal. 160 (1996) 65－75.
[74] T. Fujitani, M. Saito, Y. Kanai, T. Kakumoto, T. Watanabe, The role of metal oxides in promoting a copper catalyst for methanol synthesis, Catal. Lett. 25 (1994) 271－276.
[75] H. Oguchi, H. Kanai, K. Utani, Y. Matsumura, S. Imamura, Cu2O as active species in the steam reforming of methanol by CuO/ZrO2 catalysts, Appl. Catal. A: Gen. 293 (2005) 64－70.
[76] B. Frank, F.C. Jentoft, H. Soerijanto, J. Kröhnert, R. Schlögl, R. Schomäcker, Steam reforming of methanol over copper-containing catalysts: Influence of support material on microkinetics, J. Catal. 246 (2007) 177－192.
[77] M.A. Larrubia Vargas ,G. Busca, U. Costantino, An IR study of methanol steam reforming over ex-hydrotalcite Cu–Zn–Al catalysts, Catalysis A: Chemical 266 (2007) 188–197
[78] K.M. Minachev, K.P. Kotyaev, G.I. Lin, A.Y. Rozovskii, Temperature-programmed surface reactions of methanol on commercial Cu-containing catalysts, Catal. Lett. 3 (1989) 299－307.
[79] D. Jingfa, S. Qi, Z. Yulong, C. Songying, W. Dong, A novel process for preparation of a Cu/ZnO/Al2O3 ultrafine catalyst for methanol synthesis from CO2 + H2: comparison of various preparation methods, Appl.Catal. A 139 (1996) 75.
[80] S. Patel, K.K. Pant, Selective production of hydrogen via oxidative steam reforming of methanol using Cu–Zn–Ce–Al oxide catalysts, Chem. Eng. Sci. 62 (2007) 5436－5443.
[81] S. Patel, K.K. Pant, Hydrogen production by oxidative steam reforming of methanol using ceria promoted copper-alumina catalysts, Fuel processing Tech. 88 (2007) 825－832.
[82] M. Turco, G. Bagnasco, U. Costantino, F. Marmottini, T. Montanari, G. Ramis, G. Busca, Production of hydrogen from oxidative steam reforming of methanol I. Preparation and characterization of Cu/ZnO/Al2O3 catlaysts from a hydrotalcite-like LDH precursor, J. Catal. 228 (2004) 43－55.
[83] T.L. Reitz, P.L. Lee, K.F. Czaplewski, L.C. Lang, K.E. Popp, H.H. Kung, Time-resolved XANES Investigation of CuO/ZnO in the oxidative methanol reforming reaction, J. Catal. 199 (2001) 193－201.
[84] M. Turco, G. Bagnasco, C. Cammarano, P. Senese, U. Costantino, M. Sisani, Cu/ZnO/Al2O3 catalysts for oxidative steam reforming of methanol: The role of Cu and the dispersing oxide matrix, Appl. Catal. B: Enviro. 77 (2007) 46－57.
[85] X.R. Zhang, P. Shi, J. Zhao, M. Zhao, C. Liu, Production of hydrogen for fuel cells by steam reforming of methanol on Cu/ZrO2/Al2O3 catalysts, Fuels Furn. 83 (2003) 183－192.
[86] S. Patel, K.K. Pant, Influence of preparation method on performance of Cu(Zn)(Zr)-alumina catalysts for the hydrogen production via steam reforming of methanol, J Porous Mater. 13 (2006) 373－378.
[87] Y. Okamoto, K. Fukino, T. Imanaka, S. Teranishi, J. Phys. Chem. 87 (1983) 3740.
[88] K.T. Jung, A.T. Bell, Effects of zirconia phase on the synthesis of methanol over zirconia-supported copper, Catalysis Letters 80 (2002) 63－68.
[89] D. Bianchi, T. Chafik, M. Khalfallah, S.J. Teichner, Intermediate species on zirconia supported methanol aerogel catalysts: IV. Adsorption of carbon dioxide, Appl. Catal. A: Gen. 112 (1994) 219－235.