Methanol carbonylation, platinum

The linear CO stretching frequency for the carbonylated platinum colloid while lower than that found for surface bound CO, is in the range reported for the platinum carbonyl clusters [Pt 3 (CO) 6 ] n / sind we find that the carbonylated colloid is easily transformed into the molecular cluster [Pt 12 (CO) 24 ] (10) reaction with water. The cluster was isolated in 50 yield based on platinum content of the precipitate by extraction with tetraethylammonium bromide in methanol from the aluminum hydroxide precipitated when water is added to the aluminoxane solution. The isolation of the platinum carbonyl cluster reveals nothing about the size or structure of the colloidal platinum particles, but merely emphasizes the high reactivity of metals in this highly dispersed state. The cluster isolated is presumably more a reflection of the stability of the [Pt3(CO)6]n family of clusters than a clue to the nuclearity of the colloidal metal particles - in a similar series of experiments with colloidal cobalt with a mean particle size of 20A carbonylation results in the direct formation of Co2(CO)8. 

Platinum/A-ethylpiperidine catalysts have also been used for methyl formate synthesis via methanol carbonylation [36]. 

Beden B, Lamy C, Bewick A, Kunimatsu K. 1981. Electrosorption of methanol on a platinum electrode. IR spectroscopic evidence for adsorbed carbonyl species. J Electroanal Chem 121 343-347. 

The reaction of alcohols with CO was catalyzed by Pd compounds, iodides and/or bromides, and amides (or thioamides). Thus, MeOH was carbonylated in the presence of Pd acetate, NiCl2, tV-methylpyrrolidone, Mel, and Lil to give HOAc. AcOH is prepared by the reaction of MeOH with CO in the presence of a catalyst system comprising a Pd compound, an ionic Br or I compound other than HBr or HI, a sulfone or sulfoxide, and, in some cases, a Ni compound and a phosphine oxide or a phosphinic acid.60 Palladium(II) salts catalyze the carbonylation of methyl iodide in methanol to methyl acetate in the presence of an excess of iodide, even without amine or phosphine co-ligands platinum(II) salts are less effective.61 A novel Pd11 complex (13) is a highly efficient catalyst for the carbonylation of organic alcohols and alkenes to carboxylic acids/esters.62... 

Platinum carbonylate anion clusters like [Pt3(CO)6] can be obtained by alkaline reduction of [PtCh] in a CO atmosphere. From [Pt3(CO)s] other higher nuclear-ity anions can be obtained. In this context, several examples have been reported in which this type of anionic cluster is used in the preparation of catalysts by impregnation or exchange methods. Salts of [Pt3 (CO)6 ] (n = 3, 5) have been used to prepare, by impregnation, dispersed platinum on ZnO and MgO [49] and, by ion exchange methods, to prepare Pt3 /C electrodes for the electrocatalytic oxidation of methanol [50]. A salt of [Pti2(CO)24] has recently been used to prepare... 

Nitro group in an oxime is reduced preferentially to the oximino group with ammonium sulfide [240]. In a monoxime of a diketone, the oximino group is reduced to amino group to the exclusion of the carbonyl group by catalytic hydrogenation over platinum oxide in methanolic hydrochloric acid 9-keto-10-oximino-1,2,3,4-tetrahydrophenanthraquinone afforded 10-amino-9-keto-l,2,3,4-tetrahydrophenanthrene in 78% yield [949]. 

Cathodic surfaces of finely divided platinum, palladium and nickel have a low hydrogen overvoltage and the dominant electrochemical reaction is the generation of a layer of hydrogen atoms. The electrocatalytic hydrogenation of aldehydes and ketones can be achieved at these surfaces. Cathodes of platinum or palladium black operate in both acid solution [203] and in methanol containing sodium methoxide [204], The carbonyl compound is converted to the alcohol. Reduction of 4-tert-butylcyclohexanone is not stereoselective, however, 1,2-diphenylpropan-l-one is converted to the / reo-alcohol. 

An HP IR study of the platinum catalysed carbonylation of methanol to methyl formate, revealed that the catalyst precursor, ds-[Pt(PEt3)2Cl2] is converted into cis-[Pt(PEt3)2(CO)2] along with a cluster species, [Pt3(PEt3)3(CO) ] (n = 3 or 4) [95]. A mechanism involving oxidative addition of methanol to Pt(0) followed by CO insertion into the Pt-OMe bond was suggested. 

Cluster Compounds.—An interesting new series of platinum carbonyl dianions of formula [Pt3(CO)3(p2-CO)3]2 n = 2—5) have been synthesized by reduction of [PtClg]2" with CO and methanolic NaOH.107 Species with decreasing n were isolated with increasing concentration of reducing agent (equation 18). The X-ray... 

The electrocatalytic oxygen reduction in DMFC systems requires the development of highly selective electrodes in the presence of methanol. Present electrolyte membranes based on Nafion 117 are permeable to methanol (crossover effect), which depolarizes the platinum cathode [81,82]. For this reason, our strategy, some years ago, was to produce electrocatalytic materials from the thermal decomposition of some neutral transition-metal carbonyl compounds in the presence... 

K.-I. Machida, A. Fukuoka, M. Ichikawa, M. Enyo, Preparation of chemically modified electrodes attachement of platinum carbonyl clusters, and their efficient electrocatalytic action in anodic oxidation of methanol. J. Chem. Soc. Chem. Commun. 1987, 1486-1487. 

The selective production of methanol and of ethanol by carbon monoxide hydrogenation involving pyrolysed rhodium carbonyl clusters supported on basic or amphoteric oxides, respectively, has been discussed. The nature of the support clearly plays the major role in influencing the ratio of oxygenated products to hydrocarbon products, whereas the nuclearity and charge of the starting rhodium cluster compound are of minor importance. Ichikawa has now extended this work to a study of (CO 4- Hj) reactions in the presence of alkenes and to reactions over catalysts derived from platinum and iridium clusters. Rhodium, bimetallic Rh-Co, and cobalt carbonyl clusters supported on zinc oxide and other basic oxides are active catalysts for the hydro-formylation of ethene and propene at one atm and 90-180°C. Various rhodium carbonyl cluster precursors have been used catalytic activities at about 160vary in the order Rh4(CO)i2 > Rh6(CO)ig > [Rh7(CO)i6] >... 

The addition of platinum group metals to the Co-catalyzed carbonylation significantly lowers reaction requirements. A catalyst mixture of 2.7 parts cobalt acetate, 3 parts iodine, 1.2 parts bis(triphenylphosphine)-palladium(II) chloride and 2.4 parts adi-ponitrile converts methanol to acetic acid at 120 C and 25 MPa. 

The effect of Pt particle size on oxidation of methanol has been studied by several researchers. Machida et al. [67] introduced several platinum-cluster-attached graphite electrodes and reported enhanced electrocatalytic activity in anodic methanol oxidation with Pt clusters ranging in size from Pt9 to Ptis [67]. The catalytic activity of supported Pt clusters is significantly higher than that of conventional Pt electrodes. They used platinum carbonyl clusters of the type Pt3n,(CO)6n (u= 3,5) as well as HRu3(CO)n. Modification of the graphite surface... 

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