Selectivity and Activity of Iron Molybdate Catalysts in Oxidation of Methanol

Khalid Khazzal Hummadi, Karim H. Hassan, Phillip C.H. Mitchell

Abstract


The selectivity and activity of iron molybdate catalysts prepared by different methods are compared with those of a commercial catalyst in the oxidation of methanol to formaldehyde in a continuous tubular bed reactor at 200-350 oC (473-623 oK), 10 atm (1013 kPa), with a methanol-oxygen mixture fixed at 5.5% by volume methanol: air ratio. The iron(III) molybdate catalyst prepared by co-precipitation and filtration had a selectivity towards formaldehyde in methanol oxidation comparable with a commercial catalyst; maximum selectivity (82.3%) was obtained at 573oK when the conversion was 59.7%. Catalysts prepared by reacting iron (III) and molybdate by kneading or precipitation followed by evaporation, omitting a filtration stage, were less active and less selective. The selectivity-activity relationships of these catalysts as a function of temperature were discussed in relation to the method of preparation, surface areas and composition. By combing this catalytic data with data from the patent literature we demonstrate a synergy between iron and molybdenum in regard to methanol oxidation to formaldehyde; the optimum composition corresponded to an iron mole fraction 0.2-0.3. The selectivity to formaldehyde was practically constant up to an iron mole fraction 0.3 and then decreased at higher iron concentrations. The iron component can be regarded as the activity promoter. The iron molybdate catalysts can thus be related to other two-component MoO3-based selective oxidation catalysts, e.g. bismuth and cobalt molybdates. The iron oxide functions as a relatively basic oxide abstracting, in the rate-controlling step, a proton from the methyl of a bound methoxy group of chemisorbed methanol. It was proposed that a crucial feature of the sought after iron(III) molybdate catalyst is the presence of -O-Mo-O-Fe-O-Mo-O- groups as found in the compound Fe2(MoO4)3 and for Fe3+ well dispersed in MoO3 generally. At the higher iron(III) concentrations the loss of selectivity is due to the presence of iron oxide patches or particles which catalyze the total oxidation of methanol, and the loss of activity to blocking of molybdenum sites.

 


Keywords


Selective oxidation, Methanol, Formaldehyde, Iron molybdate, Activity

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References


Boreskov, G.K., Delmon, B., Jacobs, P.A. and Poncelet, G., 1976, "In Preparation of Catalysts," Elsevier, Amsterdam, pp. 223-227.

Bowker, M., Holroyd, R., Elliott, A., Morrall, P., Alouche, A., Entwistle, C. and Toerncrona, A., 2002, “Catalysis Letters,” Vol. 83, pp. 165-176.

Catal, T., 1997, “Mars van Krevelen,” Vol. 34, p. 40.

Dia Kov. V., Larfarge, D. and Varma, A., 2001, "Methanol Oxidation Dehydrogenation in a Catalytic Packed - Bed Membrane Reactor", Catalysis Today, Vol. 76, pp. 159-167.

Diakov, V., Blackwell, B. and Varmay, A., 2002, "Methanol Oxidative Dehydrogenation in a Catalytic Peaked-Ped Membrane Reactor; Experimental and Model," Chemical Engineering Science, Vol. 57, pp. 1563-1569.

Farrauto, R.J. and Bartholomew, C.H., 1997, “Fundamentals of Industrial Catalytic Processes,“ Blackie Academic and Professional, London, p. 489.

Ivanov, K., Mitov, I. and Kruster., "Selective Oxidation of Methanol on Fe-Mo-W Catalysts," J. of Alloys and Compounds, Vol. 309(14), pp. 57-60.

Jia-Liang, Li., Wei-Lin Dai., Ky Dong, Jing- Fa Domg, 2000, " A New Silver-Containing Ceramics for Catalytic Oxidation of Methanol to Formldehyde," Materials Letters, Vol. 44(3-4), pp. 233-236.

Le Pag, J.F. and Miquel, J.In., Delmon, B., Jacobs, P.A. and Poncelt, G., 1976, "Preparation of Catalysts,"Elsevier Amsterdam, pp. 39-43.

Le Page, J.F., 1987, "Applied Heterogeneous Catalysis," Technip Paris. McCarron, E.M. III., Sleight, A.W., Mitchell, P.C.H. and Sykes. A.G., 1986,“The Chemistry and Uses of Molybdenum,” Proceedings of the Climax Fifth International Conference, Polyhedron Synposia-in- Print Number 2, Pergamon Press, Oxford, p. 129.

Monti, D., Reller, A., and Baiker, A., 1985, "Methanol Oxidation on K2SO4- Promoted Vanadium Pentoxide; Activity, Reducibility and Structure of Catalysts,” J. of Catalysis, Vol. 93, pp. 360-367.

Powder Diffraction File, 1978, “Alphabetical Listing,” Swarthmore Pennsylvania.

Satter Filled and Charles N., 1980, "Heterogenous Catalysis in Practice," Mc Graw-Hill, Inc., New York.

Soares A.P.V, Portela M.F.,Kiennemann A.,Hilaire L. and Millet J.M.M., 2001, "Iron Molybdate Catalysts for Methanol to Formaldehyde Oxidation; Effect of Mo excess on Catalystic Behaviour," Applied Catalysis, Vol. 206, pp. 221-229.

Soares A.P.V., Portela M.F. and Kiennemanu A., 2001, "Iron Molybdate Catalysts for Methanol to form Aldehyde Oxidation; Effect of Mo Excess on the Deactivation behaviour," Catalysis Communications, Vol. 2, pp. 159-164.

Soares, A.P.V., Portela, M.F., Kiennemann, A. and Hilaire, L., 2003, “Chemical Engineering Science,” Vol. 58, pp. 1315-1322.

Soares, A.P.V., Portela, M.F. and Kiennemann, A., 1997,

“3rd World Congress on Oxidation Catalysis,” Vol. 110, 807-816.

The Formaldehyde Council, Inc. (FCI): http://www.formaldehyde.org.

Topsoe, H., Clausen, B.S., Burriescin, Candia R. and Morups, 1976, "In preparation of Catalysts,” Elsevier, Amsterdam, pp. 479-487.

Wachs I.E.,2003, "Extending Surface Science Studies to Industrial Reaction Conditions; Mechanism and Kinetics of Methanol Oxidation over Silver Surface,” Surface Science, Vol. 544, pp. 1-4.

Wachs, I.E. and Briand, L.E., 2000, “US Patent 6037290,” Lehigh University, Bethlehem, PA, USA.

Wang. C.T. and Willey, R.J., 2001, “ Journal of Catalysis,”Vol. 202, pp. 211-219.




DOI: http://dx.doi.org/10.24200/tjer.vol6iss1pp1-7

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