Surface Characterization of Supported MoO<SUB>3</SUB> Catalysts by TPR

Jin-Wook Ha

Journal of Industrial and Engineering Chemistry, Vol.4, No.3, 191-196, September, 1998

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Surface Characterization of Supported MoO₃ Catalysts by TPR

Jin-Wook Ha^†

Department of Chemical Engineering, College of Engineering, Soonchunhyang University, Asan 336-745, Korea

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Temperature programmed reduction (TPR) and X-ray diffraction (XRD) were performed for the characterization of supported MoO₃ catalysts. Silica supported MoO₃ (surface loading from 0.2 to 4.0 atoms Mo/nm²) and alumina supported MoO₃ (surface loading from 0.6 to 12.0 atoms Mo/nm²) were reduced from 400 to 1000 ℃. TPR results of physically mined samples show that bulk MoO₃ is reduced in the first reduction stage. This is in contrast to the literature where the first reduction peak is attributed to dispersed and microcrystalline of MoO₃, while the second peak is attributed to bulk MoO₃. It is also noted that the area of the first TPR peak is close to half that of the second TPR peak. This implies that MoO₃ crystals are reduced over supports by a two step process as Mo⁶⁺→Mo⁴⁺→Mo metal. Finally, the reduction mechanism over silica can be described as a simultaneous, parallel pathway for both types of species (polymolybdate and crystalline MoO₃). And well dispersed polymolybdate (peak maximum at 490 ℃) is reduced more easily than bulk MoO₃ (peak maximum at 540 ℃) over alumina.

Keywords:MoO₃;TPR;SiO₂;Al₂O₃

[References]

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[1] Gentry SJ, Walsh PT, J. Chem. Soc.-Faraday Trans., 78, 1515 (1982)

[2] Jacobs PA, Linart J, Nijs H, Uytterhoeven JB, J. Chem. Soc.-Faraday Trans., 73, 1745 (1977)

[3] Wagstaff N, Prins R, J. Catal., 59, 434 (1979)

[4] Isaacs BH, Petersen EE, J. Catal., 77, 43 (1982)

[5] Lycourghiotis A, Defosse C, Delannay F, Lemaitre J, Delmon B, J. Chem. Soc.-Faraday Trans., 75, 1677 (1980)

[6] Gentry SD, Hurst NW, Jones A, J. Chem. Soc.-Faraday Trans., 77, 603 (1981)

[7] Nurst NW, Gentry SJ, Jones A, McNicol BD, Catal. Rev.-Sci. Eng., 24, 233 (1982)

[8] Monti DAM, Baiker A, J. Catal., 83, 323 (1983)

[9] Massoth FE, Adv. Catal., 28, 265 (1978)

[10] Thomas R, vanOers EM, deBeer VHJ, Mdedma J, Moulijn JA, J. Catal., 76, 241 (1982)

[11] Thomas R, vanOers EM, deBeer VHJ, Moulijn JA, J. Catal., 84, 275 (1983)

[12] Nag NK, Frankel D, Moulijn JA, Gates BC, J. Catal., 66, 162 (1980)

[13] Yao HC, J. Catal., 70, 440 (1981)

[14] Brito J, Laine J, Polyhedron, 5(1-2), 179 (1986)

[15] delArco M, Carrazan SRG, Rives V, Gil-Llambias FT, Malet P, J. Catal., 141, 48 (1993)

[16] Caceres CV, Fierro JL, Lopez-Agudo A, Blanco MN, Thomas HJ, J. Catal., 95, 501 (1985)

[17] Datta AK, Ha JW, Regalbuto JR, J. Catal., 133, 55 (1992)

[18] Ismail HM, Zaki MI, Bond GC, Shukri R, Appl. Catal., 72, L1 (1991)

[19] deBoer M, Ph.D. Dissertation, University of Amsterdam, The Netherlands (1992)

[20] Williams CC, J. Phys. Chem., 95, 8781 (1991)