Synergism and Kinetics in CO Oxidation over Palladium-Rhodium Bimetallic Catalysts

Yoon KJ; Kang HK; Yie JE

Korean Journal of Chemical Engineering, Vol.14, No.5, 399-406, September, 1997

The activity and kinetics of CO oxidation over alumina-supported Pd-Rh bimetallic catalysts were investigated. One bimetallic catalyst, Pd-Rh(2), was prepared by two-step impregnation and another, Pd-Rh(1), by simultaneous impregnation. Monometallic catalysts as well as a physical mixture of them were also prepared. The catalysts were characterized by selective chemisorption of both H2 and CO, and an attempt was made to determine the surface compositions of the bimetallic catalysts. The bimetallic catalysts showed different kinetic behavior, such as higher turnover frequencies (TOFs), lower apparent activation energies and/or negative reaction orders for CO which were smaller in the absolute value, from that of the monometallic catalysts as well as a physical mixture of them. It is suggested that this Pd-Rh synergism is due to an interaction on the catalyst surface, such that adsorbed CO or oxygen on one metal migrates to the other metal site so that the reaction rate is facilitated and also that the particles of Pd and Rh are located close enough to each other for the interaction to occur. On the surface of Pd-Rh(2) most of the Pd and Rh particles existed as separate entities, while a great portion or the particles on Pd-Rh(1) exhibited the surface enrichment of Pd. This explains the higher TOF and the negative reaction orders for CO over Pd-Rh(2) which were smaller in the absolute value than those over Pd-Rh(1)

Keywords:CO Oxidation;Kinetics;Palladium-rhodium;Surface Composition;Synergism

[References]

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[Referenced By]

[1] Anderson JR, Pratt KC, "Introduction to Characterization and Testing of Catalysts," Chap. 1, Academic Press, North Ryde, Australia (1985)

[2] Benson JE, Hwang HS, Boudart M, J. Catal., 30, 146 (1973)

[3] Berlowitz PJ, Penden CHF, Goodman DW, J. Phys. Chem., 92, 5213 (1988)

[4] Boudart M, Djega-Mariadassou G, "Kinetics of Heterogeneous Catalytic Reactions," p. 69, and p. 157, Princeton University Press, Princeton (1984)

[5] Choi KI, Vannice MA, J. Catal., 131, 1 (1991)

[6] Eischens RP, Pliskin WA, Adv. Catal. Related Subjects, 10, 1 (1958)

[7] Emmett PH, Brunauer S, J. Am. Chem. Soc., 59, 310 (1937)

[8] Engel T, Ertl G, Adv. Catal., 28, 1 (1979)

[9] Fisher GB, Zammit MG, Labarge WJ, Automotive Eng., 100, 37 (1992)

[10] Foger K, "Dispersed Metal Catalysts," in "Catalysis-Science and Technology," Anderson, J.R. and Boudart, M., Eds., Springer-Verlag, Berlin, 6, 227 (1984)

[11] Goodman DW, Penden CHF, J. Phys. Chem., 90, 4839 (1986)

[12] Heck RM, Farrauto RJ, "Catalytic Air Pollution Control: Commercial Technology," Chap. 6, Van Nostrand Reinhold, New York (1995)

[13] Ioannides T, Efstathiou AM, Zhang ZL, Verykios XE, J. Catal., 156(2), 265 (1995)

[14] Jung HJ, Walker PL, Vannice MA, J. Catal., 75, 416 (1982)

[15] Kaminsky M, Yoon KJ, Geoffroy GL, Vannice MA, J. Catal., 91, 338 (1985)

[16] Kim SI, Yoon KJ, HWAHAK KONGHAK, 34(5), 658 (1996)

[17] Kim Y, Shi SK, White JM, J. Catal., 61, 374 (1980)

[18] Knor Z, Catal. Rev.-Sci. Eng., 1, 257 (1968)

[19] Landry SM, DallaBetta RA, Lu JP, Boudart M, J. Phys. Chem., 94, 1203 (1990)

[20] Logan AD, Paffett MT, J. Catal., 133, 179 (1992)

[21] Lui Y, Dettling J, "Evolution of a Pd/Rh TWC Catalyst Technology," SAE 930249 (1993)

[22] Matsushima T, Almy DB, Foyt DC, Close JS, White JM, J. Catal., 39, 277 (1975)

[23] Moss RL, "Preparation and Characterization of Supported Metal Catalysts," in "Experimental Methods in Catalytic Research," Anderson, R.B. and Dawson, P.T., Eds., Academic Press, New York, 2, 43 (1976)

[24] Moss RL, Whalley L, Adv. Catal., 22, 115 (1972)

[25] Oh SE, Carpenter JE, J. Catal., 80, 472 (1983)

[26] Oh SE, Carpenter JE, J. Catal., 98, 178 (1986)

[27] Oh SE, Eickel CC, J. Catal., 128, 526 (1991)

[28] Oh SH, Fisher GB, Carpenter JE, Goodman DW, J. Catal., 100, 360 (1986)

[29] Park SD, Lee IW, Choi MJ, Hong SI, HWAHAK KONGHAK, 30(5), 571 (1992)

[30] Sachtler WMH, Catal. Rev.-Sci. Eng., 14, 193 (1976)

[31] Satterfield CN, "Heterogeneous Catalysis in Practice," McGraw-Hill, New York, 313 (1980)

[32] Schlatter JC, Taylor KC, J. Catal., 49, 42 (1977)

[33] Smith JM, "Chemical Engineering Kinetics," McGraw-Hill Kogakusha, Tokyo, 470 (1981)

[34] Somorjai GA, Catal. Rev.-Sci. Eng., 23, 189 (1981)

[35] Taylor KC, Ind. Eng. Chem. Prod. Res. Dev., 15, 264 (1976)

[36] Taylor KC, "Automobile Catalytic Converters," in "Catalysis-Science and Technology," Anderson, J.R. and Boudart, M., Eds., Springer-Verlag, Berlin, 5, 119 (1984)

[37] Vannice MA, "Catalytic Activation of Carbon Monoxide on Metal Surfaces," in "Catalysis-Science and Technology," Anderson, J.R. and Boudart, M., Eds., Springer-Verlag, Berlin, 3, 139 (1982)

[38] Williamson WB, Lewis D, Perry J, Gandhi HS, Ind. Eng. Chem. Prod. Res. Dev., 23, 531 (1984)

[39] Wong C, McCabe RW, J. Catal., 119, 47 (1989)

[40] Yang AC, Garland CW, J. Phys. Chem., 61, 1504 (1957)

[41] Yao YFY, J. Catal., 87, 152 (1984)

[42] Yoon KJ, Kim EJ, Korean J. Chem. Eng., 12(2), 221 (1995)