Kinetics of the partial oxidation of methanol over a Fe-Mo catalyst S.A.R.K. Deshmukh * , M. van Sint Annaland, J.A.M. Kuipers Faculty of Science and Technology, University of Twente, P.O. Box 217, 7500 AE, The Netherlands Received 13 March 2005; received in revised form 26 March 2005; accepted 10 May 2005 Available online 16 June 2005 Abstract The intrinsic steady-state kinetics of the partial oxidation of methanol to formaldehyde over a commercial Fe-Mo catalyst has been studied experimentally in a differentially operated reactor at temperatures of 230–260 8C, over a wide range of methanol and oxygen concentrations. The principal products found were formaldehyde, water, dimethyl ether (DME) and dimethoxymethane (DMM). The kinetics of the formaldehyde formation from methanol could be well described with Langmuir–Hinshelwood kinetics, assuming two different metal oxide sites, one containing adsorbed oxygenates and the other one containing lattice oxygen. The presence of water vapor lowered the formaldehyde formation rate significantly, especially at lower water partial pressures. These results could be well explained in terms of competitive adsorption of water with methanol on the free active catalyst sites. For the most important side reactions, i.e. dimethyl ether formation as well as dimethoxymethane formation the forward reaction rates were determined from the selectivity data. The conversion rate of dimethyl ether to formaldehyde was also measured with separate experiments in the differential reactor. Carbon monoxide was not formed during the differential kinetic measurements of formaldehyde formation from methanol. Therefore, the rate of formaldehyde oxidation to CO was studied separately in a dual bed catalyst, where formaldehyde was formed in the first integral reactor at low temperatures and subsequently converted to CO in a differential reactor. The rate of CO formation was first order in formaldehyde and the oxygen dependency was the same as that for the formaldehyde formation from methanol. Rate expressions for all reactions were formulated based on the above assumptions and a multivariate Levenberg–Marquardt method was used to fit all the model constants to all the experiments for all reaction rates simultaneously, while additionally accounting for axial concentration profiles in the reactor. The observed influences of composition and temperature on the reaction rates could be well described. # 2005 Elsevier B.V. All rights reserved. Keywords: Catalytic oxidation; Methanol; Formaldehyde; Carbon monoxide; Kinetics; Differential reactor 1. Introduction Formaldehyde is a base chemical of major industrial importance. In spite of fluctuations in the world economy, the growth of formaldehyde production has been remarkably steady and is expected to continue. The main industrial use of formaldehyde is in the production of urea-phenolic and melamine resins, which are used in the manufacture of chipboard (compressed wood) and plywood. Other well- established applications are in the production of paints, cosmetics, explosives, fertilizers, dyes, textiles and papers. Industrial processes for formaldehyde production can be divided in silver-catalyzed and metal oxide catalyzed processes. Most of the newly built formaldehyde plants (more than 70%) are based on the metal oxide catalyst (Fe- Mo) due to near complete conversion of methanol (exceeding 99%) as well as very high formaldehyde selectivity (95%) and, most importantly, due to stringent environmental regulations being imposed. In this process, all of the formaldehyde is produced by the exothermic partial oxidation of methanol, essentially at atmospheric pressures and temperatures of 250–400 8C. Overall plant yields are 88–92% [1]. Generally, a multitubular non-adiabatic packed bed reactor, with the heat transfer fluid flowing on the shell side, is used. The feed to the reactor is lean in methanol and rich in oxygen. However, if the oxygen in the reactor is www.elsevier.com/locate/apcata Applied Catalysis A: General 289 (2005) 240–255 * Corresponding author. Tel.: +31 534894478; fax: +31 534892882. E-mail address: salim_deshmukh@yahoo.com (S.A.R.K. Deshmukh). 0926-860X/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2005.05.005