Copper methanol dehydrogenation

This study reports improved stabilities of skeletal Cu catalysts for use in organic synthesis reactions. The promoted skeletal Cu catalysts have been characterised by measuring their resistance to structural rearrangement in caustic solutions, thermal stabilities and activities for the reactions of methanol dehydrogenation and methyl formate hydrogenolysis. Comparisons have been made with an unpromoted skeletal Cu catalyst and a commercial coprecipitated copper chromite catalyst. 

Hoffmaim developed flameless combustion of methanol in 1867. He used a platinum coil as a caMyst that glowed red hot as the methanol dehydrogenated and produced some formaldehyde. A commercial plant was designed by Trillat in 1889 to convert a methanoFair mixture into formaldehyde nsing a platinized asbestos catalyst. Trillat subsequently showed that other catalysts could also be used, such as oxidized copper at 330°C, although platinum at 200°C was most effective. Yields of about 50% formaldehyde were produced and he claimed that the addition of 20% steam to the gases improved performance. 

In the presence of metallic copper, metallic silver, or a copper-silver alloy used in the form of gauze or as metal deposited on a low surface area inert support, methanol can be dehydrogenated to formaldehyde at 400—500°C. 

In order to recognize the pattern of reactivity of alcohols on modified nickel surfaces, it is essential to know the reaction pathways exhibited by less reactive surfaces. Initially the dehydrogenation of CH3OH was studied on copper (4 ) and silver (5 ) single crystal surfaces. On Cu(110), following the preadsorption of submonolayer quantities of atomic oxygen, methanol reacted via the following sequence (4,6) ... 

Two major pathways for CSRM have been suggested using copper-based catalysts (i) a decomposition-WGSR sequence and (ii) dehydrogenation of methanol to methyl formate (Equation 6.7). 

It includes the steam reforming of methane over a nickel catalyst to synthesis gas followed by the copper-catalyzed transformation of the latter to methanol (see Section 3.5.1). Finally, formaldehyde is produced by oxidative dehydrogenation of methanol. 

Copper-catalysts promoted with i) other group VIA or VIIIA metals and ii) alcaline or alcaline earth elements (IA or IIA) are used for selective hydrogenation of various organic compounds (1). Moreover Cu(Co) Zn-Al catalysts were extensively studied for the synthesis of methanol and of light alcohols (2,3). More recently, due to the development of fine chemical processes, detailed studies of copper catalysts were carried out in order to show, like for noble metals, the effect of supports (SMSI), of promoters and of activation-on metal dispersion or reduction, on alloy formation... For example modified copper catalysts are known for their utilization in the dehydrogenation of esters (4-6), in the hydrolysis of nitriles (7), in the selective hydrogenation of nitriles (8), in the amination of alcohols (9)... 

In some cases, the reaction of silicon and methanol has been optimized for formation of (MeO)4Si. As discussed above, thiophene addition favored formation of (MeO SiH. Both thiophene and propyl chloride poison copper copper poisoning seems to favor formation of the trialkoxysilane. High-temperature pretreatment disfavors trialkoxysilane formation copper is formed on the surface of the silicon during pretreatment at 450 °C98. Metallic Cu catalyzes dehydrogenation of alcohols and favors formation of (RO)4Si. Workers from Tonen Corporation reported 50% conversion of silicon to make (MeO Si with 92% selectivity if silicon, methanol and Cu(OMe)2 were pretreated (lower conversion and selectivity without pretreatment) and then reacted at 180 °C and 1 atmosphere99. 

Skeletal Cu-Zn catalysts show great potential as alternatives to coprecipitated Cu0-Zn0-Al203 catalysts used commercially for low temperature methanol synthesis and water gas shift (WGS) reactions. They can also be used for other reactions such as steam reforming of methanol, methyl formate production by dehydrogenation of methanol, and hydrogenolysis of alkyl formates to produce alcohols. In all these reactions zinc oxide-promoted skeletal copper catalysts have been found to have high activity and selectivity. 

Takezawa N, Iwasa N. Steam reforming and dehydrogenation of methanol difference in the catalytic functions of copper and group VIII metals. Catal Today. 1997 36(l) 45-56. 

The methanol is dehydrogenated in the gas phase around I90. at atmospheric pressure, in the presence of a copper-based catalyst on a support, promoted by other metals such as Zr, Zn. M etc... 

Dehydrogenation of methanol over copper containing catalysts at the temperature range 200—400° C is achieved by two Hnearly indepen dent stepwise channels... 

The catalytic activities of metal ion-exchanged TSMs for the methanol conversion are individually different, depending on the metal ion. Figure 8 shows the attractive reactions found in this study. It is of particular interest that the catalytic activity of copper varies depending on the oxidation state. Cu -TSM is inactive, whereas Cu " - and Cu°-TSMs catalyze selectively the dehydrogenation of methanol to methyl formate and to formaldehyde, respectively. Cu -TSM has potential for practical use because of its high stability and high selectivity for the methly formate formation. 

The condensation of a, dicarbonyl compounds (49) with aj3-diamino compounds (50), which proceeds through the dihydropyrazine (51), has been much used for the synthesis of alkyl- and arylpyrazines (52). These reactions are usually carried out in methanol, ethanol, or ether in the presence of sodium or potassium hydroxide. The dihydropyrazines may be isolated, or oxidized directly to the pyrazine. Dehydrogenating agents that have been employed include oxygen in aqueous alkali (329), air in the presence of potassium hydroxide (330), sodium amylate in amyl alcohol (330a), alcoholic ferric chloride (24), and copper chromite catalyst at 300° (331) (see also Section 1). Pyrazines prepared by this method and modifications described below are listed in Table II.8 (2, 6, 24, 60, 80,195, 329-382) and some additional data are provided in Sections VI. 1 A, VlII.lA(l), and IX.4A(1). 

Supported copper-based catalysts are active for a great variety of reactions and there have been many fundamental studies of their catalytic and solid state properties. Among them, the oxidation of hydrocarbons and CO (1), alkanes (2) and alcohols (3) dehydrogenation, hydrogenation of ketones (4), allyl alcohols and a- and 6-unsaturated aldehydes and ketones (5), alcohol amination (6), low temperature water gas shift (7). methanol synthesis (8), oxidative condensation of methanol (9), hydrolysis of acrylonitrile to acrylamide (10), and removal of NOx pollutants (11). 

Introduction.—The oxidative dehydrogenation of alcohols to aldehydes and ketones over various catalysts, including copper and particularly silver, is a well-established industrial process. The conversion of methanol to formaldehyde over silver catalysts is the most common process, with reaction at 750—900 K under conditions of excess methanol and at high oxygen conversion selectivities are in the region 80—95%. Isopropanol and isobutanol are also oxidized commercially in a similar manner. By-products from these reactions include carbon dioxide, carbon monoxide, hydrogen, carboxylic acids, alkenes, and alkanes. 

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