Molybdate methanol oxidation

Figure 2 Microprobe Raman analysis of an iron-molybdate methanol oxidation catalyst (a) mixture of M0O3 and Fe2(Mo04)3 (b) Fe2(Mo04)3 (c) M0O3.

Ruthenium on platinum was found to promote the oxidation of AoCOad while tin on platinum was found effective for eoCOad. Enhancement of the methanol oxidation to CO2 was confirmed on platiniua with either rutheniiim or tin. Molybdates on platinum was also found to promote the oxidation of botheoCOad ai d methanol. 

Ruthenium, tin and molybdates all showed enhancement effects on the COad oxidation and the methanol oxidation. The effects are compared in Table 4-1. 

Both ruthenium and tin showed gieat enhancement effects on the methanol oxidation also. On the contrary, only slight effects were seen for molybdate probably because of its low working potential range where COad formation is not very fast. 

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. 

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. 

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... 

In the following we will investigate the methanol oxidation process over silver, copper and heteropoly molybdates in order to identify the occurrence of the possible reaction pathways from Schemes 2 and 3 on polycrystalline surfaces and at atmospheric pressure. The main emphasis in these experiments will be on the source of active oxygen. This focus was chosen to better understand the involvement of bulk and sub-surface [10,48] chemistry in selective oxidation catalysis. Such an understanding is required when the catalytic performance is compared between series of chemically different systems which are chosen to investigate only one surface property such as acidity. These experiments will naturally only cover a small selection of the problems discussed with the reaction Schemes. 

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

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. 

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 ... 

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. 

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. 

Briand, L., Hirt, A. and Wachs, I. (2001). Quantitative Determination of the Number of Surface Active Sites and the Turnover Frequencies for Methanol Oxidation over Metal Oxide Catalysts Application to Bulk Metal Molybdates and Pure Metal Oxide Catalysts, J. Catal., 202, pp. 268-278. 

Briand, L.E., Hirt, A.M., and Wachs, I.E. Quantitative determination of the number of surface active sites and the turnover frequencies for methanol oxidation over metal oxide catalysts Application to bulk metal molybdates and pure metal oxide catalysts. J. Catal. 2001, 202, 268-278. 

Wachs, I.E. and Briand, L.E. In situ Formation of Iron-Molybdate Catalysts for Methanol Oxidation to Formaldehyde. U.S. patent No. 6,331,503 Bl, December 18,2001. 

Benzene oxidation to maleie anhydride. Methanol oxidation to formaldehyde (iron molybdate catalyst). 

Different Fe203/Mo03 catalysts were prepared by kneading, precipitation and co-precipitation methods. Their activities and selectivities in the oxidation of methanol to formaldehyde were compared with those of a commercial catalyst. 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 573 K when the conversion was 59.7%. Catalysts prepared by reacting iron(IIl) and molybdate by kneading or precipitation followed by evaporation, omitting a filtration stage, were less active and less selective. 

Oxidation Catalysis. The multiple oxidation states available in molybdenum oxide species make these exceUent catalysts in oxidation reactions. The oxidation of methanol (qv) to formaldehyde (qv) is generally carried out commercially on mixed ferric molybdate—molybdenum trioxide catalysts. The oxidation of propylene (qv) to acrolein (77) and the ammoxidation of propylene to acrylonitrile (qv) (78) are each carried out over bismuth—molybdenum oxide catalyst systems. The latter (Sohio) process produces in excess of 3.6 x 10 t/yr of acrylonitrile, which finds use in the production of fibers (qv), elastomers (qv), and water-soluble polymers. 

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