Methanol oxidation iron molybdate

The methanol oxidation iron-molybdate process takes place in a shell-and-tube fixed-bed reactor where the catalysts are packed within the tubes and the circulating oil coolant maintains catalyst temperatures of 350-450°C, with the higher temperatures occurring in the hot spot region. The process is conducted at 100% methanol conversion with greater than 90% formaldehyde selectivity, which results in formaldehyde yields greater than 90%. The higher formaldehyde yield of the methanol oxidation iron-molybdate process makes it the preferred process for new plants. 

House, M., Carley, A. and Bowker, M. (2007). Selective Oxidation of Methanol on Iron Molybdate Catalysts and the Effects of Surface Reduction, J. Catal., 252, pp. 88-96. 

Iron molybdates, well known as selective methanol oxidation catalysts, are also active for the propene oxidation, but not particularly selective with respect to acrolein. Acetone is the chief product at low temperature (200°C), whereas carbon oxides, besides some acrolein, predominate at higher temperatures [182,257], Firsova et al. [112,113] report that adsorption of propene on iron molybdate (Fe/Me = 1/2) at 80—120°C causes cation reduction (Fe3+ -> Fe2+) as revealed by 7-resonance spectroscopy. Treatment with oxygen at 400°C could not effect reoxidation (in contrast to similarly reduced tin molybdate). The authors assume that this phenomenon is related to the low selectivity of iron molybdate. 

Selective oxidation of methanol is the industrial route to formaldehyde. In practice, two types of process are used, differing with respect to the catalyst and process conditions. Silver is a very active catalyst at 600— 700°C and requires a high methanol/oxygen ratio for a good selectivity, while iron molybdate catalysts are already active at 350° C and may be used with low methanol/oxygen ratios. 

Pernicone et al. [253,254] bring forward some evidence that surface acidity also plays a role with iron molybdate catalysts. Hammett indicators adsorbed over the molybdate assume the acid colour. Pyridine poisons the oxidation of methanol to formaldehyde. A correlation is reported between acidity and activity [253]. The authors agree with Ai that the acid sites are connected with Mo6+ ions. 

Iron oxide is an important component in catalysts used in a number of industrially important processes. Table I shows some notable examples which include iron molybdate catalysts in selective oxidation of methanol to formaldehyde, ferrite catalysts in selective oxidative dehyrogenation of butene to butadiene and of ethylbenzene to styrene, iron antimony oxide in ammoxidation of propene to acrylonitrile, and iron chromium oxide in the high temperature water-gas shift reaction. In some other reactions, iron oxide is added as a promoter to improve the performance of the catalyst. 

Methanol Oxidation. - The selective oxidation of methanol to formaldehyde by vanadium-containing catalysts has been widely studied even though in practice only iron molybdate and Ag catalysts are used for this reaction. 

A good example of the latter case is the reaction of iron with silica in silica-supported iron molybdate, a fact which made impossible the use of silica as a support in the case of catalysts used for the oxidation of methanol to formaldehyde. Some of the methods to overcome these difficulties in catalyst preparation are the subject of this section. 

Raman investigation by Hill and coworkers (Wilson et al., 1990) of bulk and supported iron molybdate catalysts during methanol oxidation to formaldehyde. This Raman reaction cell was designed to minimize void... 

The mechanism for the oxidation of methanol to formaldehyde on iron molybdate catalysts (illustrated in Figure 4) envisages the H-abstraction and electron transfer of surface methoxy species desorption of the products and reoxidation of metal sites complete the cycle. 

The selective oxidation of methanol to formaldehyde is a technologically relevant [1,2] reaction carried out over metallic silver or iron-molybdate catalysts. The reaction is also suitable as a model reaction to understand the chemical principles of modifying the oxidizing potential for dissociated oxygen on various surfaces [3,4,5,6,7]. 

A COMPARISON OF IRON MOLYBDATE CATALYSTS FOR METHANOL OXIDATION PREPARED BY COPRECIPTATION AND NEW SOL-GEL METHOD... 

Formaldehyde is nowadays one of the major produced chemicals due to its uses in many fields of chemical industry [1]. The commercial production started in 1890 using metallic copper catalysts. In 1910 copper catalysts were replaced by silver catalysts with higher yields [2]. Although the first report of the excellent catalytic behavior of iron molybdates in selective oxidation of methanol to formaldehyde is of 1931, the related industrial process based on them only went into operation in 1940-50 [1]. A recent report [3] shows that iron molybdates and silver catalysts are nowadays equally used as industrial catalysts for formaldehyde production. 

Sol-gel techniques provide interesting routes to prepare iron molybdates catalysts for selective oxidation of methanol. Catalysts prepared by this method have higher surfiice areas than catalysts prepared by coprecipitation techniques what allows to operate at lower tempo tures with the advantage of limiting the consecutive oxidation of formaldehyde to CO. 

Petrini, G., F.Gaibasa, M. Petrera and N. Pemicone, Study of Iron(II) Molybdate as Precursor of Catalysts for Methanol Oxidation to Formaldehyde , in Chemistry and Uses of Molybdetmm, Ed. H. F. Barry and P. C. Mitchell, p.437. Climax Molybdenum Company, Ann Arbor, Michigan, USA (1982). 

The selective oxidation of methanol to give formaldehyde is in practice performed in two different processes, one using metallic silver, the other using iron molybdate as catalyst. Vanadium oxide has been shown to be a good selective catalyst in a variety of oxidation processes (refs. 1-2) and we have previously shown that it is also selective for methanol oxidation (refs. 3-5) when the V Og is applied as a very thin layer (monolayer) on different supports the support can have a significant influence on the activity and selectivity of these monolayer catalysts, as was shown by Roozeboom (ref. 6). In a previous paper (ref. 5), it was shown that both the type of support (A Og or TiC ) and the crystal structure of the TiO have an influence on the selectivity of the catalyst for the production of formaldehyde in general, production of the formaldehyde increases with a decrease in the reducibility of the vanadia. 

For example transition metal such as M0O3 and Cr203, are good catalysts for polymerization of olefins a mixture of copper on chromium oxides, called copper chromite, is used for hydrogenation and, a mixture of iron and molybdenum oxide, called iron molybdate, is used for formaldehyde formation from methanol. 

A kinetic study of methanol oxidation over stoichiometric iron molybdate catalyst was performed in a fixed-bed integral reactor showing kinetic influences of reaction products. In the temperature range of 548-618 K it was not possible to fit the fomoation rate data to a single power rate law. Dimethyl ether formation presents only a second order dependence with respect to methanol. CO formation seems to be inhibited by water and formaldehyde and rate data fit well to the power rate law ... 

Iron molybdates are industrial catalysts for selective oxidation of methanol to formaldehyde [1]. Since the pioneer work of Atkins et al [2] in 1931, a large number of papers and patents has been published and the catalytic systems his relatively well characterised. 

Many kinetics studies have been performed for methanol to formaldehyde oxidation over iron molybdates. The majority of authors accept a Mars van Krevelen mechanism. However a great number of kinetic laws have been presented for this reaction. 

Bulk catalysts comprise mainly active substances, but some binder is often added to aid the forming/shaping operation. This is the case for iron oxide for the water-gas shift (WGS) reaction, iron molybdate for the oxidation of methanol to formaldehyde, and vanadyl pyrophosphate for butane oxidation to maleic anhydride. However, in some cases, bulk catalysts are used as prepared, without the need for addition of the binder. Typically, this involves catalysts prepared by high temperature fusion (eg, the iron-based ammonia synthesis catalyst). The need for the addition of binder, or the requirement for pelleting, solely depends on the strength required for the catalyst under the reaction conditions and the reactor type that is used in. This requires consideration of attrition resistance, and oxide... 

Formaldehyde is produced by oxidation of methanol or oxidative dehydrogenation of methanol. Oxidation of methanol (route (a) in Topic 5.3.2] is a strongly exothermic reaction (AH = -243 kj mol ) that is carried out in a pressure-less oxidation with air in a multi-tubular reactor. The reaction is catalyzed by an iron/molybde-num oxide contact, with Fe2(Mo04) being the active catalytic species. The oxidation is carried out at 350 °C with quantitative methanol conversion. The main side reaction is the total oxidation of methanol to CO2 and water. 

The selective oxidation of CH3OH to HCHO represents the industrial production of one of the major chemical intermediates. Two different catalytic oxidation industrial processes are in use for methanol oxidation. One process employs unsupported silver catalysts and the other employs bulk iron-molybdate, Fe2(Mo04)3, catalysts. The silver catalyst process is used when limited amounts of formaldehyde are desired and the process can be quickly started and shut down. 

Routray, K., Zhou, W., Kiely, C., et al. (2010). Origin of the Synergistic Interaction Between M0O3 and Iron Molybdate for the Selective Oxidation of Methanol to Formaldehyde, J. Catal., 275, pp. 84-98. 

Soares A., Portela M. and Kiennemann A. (2005). Methanol Selective Oxidation to Formaldehyde over Iron-molybdate Catalysts, Catal. Rev. Sci. Eng., 47,125-174. 

House, M., Carley, A., Echevenia-Valda, R., et al. (2008). Effect of Varying the Cation Ratio within Iron Molybdate Catalysts for the Selective Oxidation of Methanol, J. Phys. Chem. C, 112, pp. 4333-4341. 

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