S. M. Yunusov

Anionic ruthenium cluster K2[Ru4(CO)13] as precursor of catalytically active ruthenium particles and potassium promoter. New efficient ammonia synthesis catalysts based on supported K2[Ru4(CO)13]

Abstract New efficient potassium-promoted catalysts for ammonia synthesis are reported. For preparation of the catalysts, anionic ruthenium cluster K2[Ru4(CO)13] was used as a precursor of both catalytically active metal particles and potassium promoter while magnesium oxide and new original graphite-like active carbon CFC-1 were employed as supports. The catalysts found are capable of catalysing the ammonia synthesis starting from 250°C (1 atm) and exceed markedly in their activity at 300–400°C and atmospheric pressure the industrial ammonia synthesis catalyst (SA-1). Especially effective is the K2[Ru4(CO)13] catalyst on MgO. The replacement of MgO by γ-Al2O3 and SiO2 results in a sharp decrease in activity of the catalyst in ammonia synthesis. This indicates the importance of the basic properties of a support for the achievement of high ammonia synthesis rates.

The effect of Co and Ir on the activity of the K2[Fe2(CO)8]- and K2[Ru4(CO)13]-based systems in ammonia synthesis.: The synergistic acceleration of the ammonia synthesis over the K2[Fe2(CO)8]+K catalysts by iridium

The effect of Co and Ir on the ammonia synthesis over the K2[Fe2(CO)8]+K and K2[Ru4(CO)13]+K catalysts on graphite-like active carbon “Sibunit” has been investigated. The catalysts were prepared by depositing K2[Fe2(CO)8] and K2[Ru4(CO)13] onto the “Sibunit” carbon-supported Co and Ir, followed by thermal decomposition of the deposited cluster and treatment of the resulting sample with metallic potassium. The catalysts containing no potassium metal have been studied as well. It has been found that the presence of Co in the Ru catalysts substantially decreases the ammonia synthesis rate. Similar results have been obtained on testing the Ru–Ir samples. By contrast, the introduction of Ir in the K2[Fe2(CO)8]+K catalysts leads to a synergistic acceleration of the process of the ammonia synthesis. The strongest accelerating effect of Ir is observed at 200°C. A rise in the reaction temperature to 250, 300 and then to 350°C results in a gradual weakening of the Fe–Ir synergism. An important feature of the Fe–Ir catalysts found is their increased activity in the ammonia synthesis at 150°C. The presence of Co in the iron catalysts little affects, in general, the ammonia synthesis rate, although some acceleration of this process by Co at 350 and 400°C for the samples not treated with potassium metal can be noted.

On the path to catalysts for the low-temperature ammonia synthesis

A nontraditional approach to the development of catalysts for low-temperature ammonia synthesis is considered. The approach is characterized by application of catalysts representing heterogeneous analogs of the known homogeneous nitrogen-fixing systems based on transition metal compounds and strong electron donors. The use of this approach led to the development of catalysts that considerably surpass in their activity (at atmospheric pressure) the industrial catalyst for the ammonia synthesis. Some of the developed catalysts are active in the formation of ammonia from dinitrogen and dihidrogen even at 110–150°C. The mechanisms of activation and hydrogenation of dinitrogen over these new catalysts are discussed.

Sodium-potassium synergism in the alkylation of toluene and naphthalene with ethene in C10H8−Na−K systems in THF

Sodium-potassium synergism in the alkylation of toluene and naphthalene with ethene in naphthalene-alkali metal systems in THF was discovered. In the case of toluene, the maximum synergistic effect is observed at an Na∶K molar ratio of 1∶1. With this Na∶K molar ratio, the yields of the products of toluene alkylation with ethene considerably increase. The efficiency of naphthalene alkylation (in the presence of toluene) is also markedly enhanced on replacement of sodium or potassium by their mixture.

H-D exchange on graphite–potassium intercalation compounds

Potassium graphite intercalation compounds are able to activate C–H bonds of hydrocarbons at room temperature. In this paper, the hydrogen–deuterium exchange of CHD3 in the presence of C8K, C24K and C36K is described.

Coordination chemistry of anticrowns. Synthesis and structure of a complex of cyclic trimeric perfluoro-o-phenylenemercury (o-C6F4Hg)3 with tungsten hexacarbonyl

The reaction of the three-mercury anticrown (o-C6F4Hg)3 (1) with tungsten hexacarbonyl in CH2Cl2 at 20 °C in the dark affords the complex {[(o-C6F4Hg)3]2[W(CO)6]} (2) containing two anticrown molecules per W(CO)6 molecule. According to the X-ray diffraction data, two carbonyl groups of W(CO)6 are involved in the formation of 2, each of these carbonyl groups being coordinated via the oxygen atom to a single mercury center of one of the two molecules 1. The formation of the complex is accompanied by a shift of ν(CO) bands in the IR spectrum with respect to the corresponding bands of the starting W(CO)6.

Transformations of cyclohexa-1,4-diene under the action of biphenyl—alkali metal systems in THF. Synergistic acceleration by mixtures of lithium and sodium

In the interaction of cyclohexa-1,4-diene (1,4-CHD) with a mixture of biphenyl and metallic lithium or sodium in THF at 20 °C, three processes occur, viz., disproportionation of 1,4-CHD to form benzene and cyclohexene, dehydrogenation of 1,4-CHD to form benzene and molecular hydrogen, and dehydrogenation of 1,4-CHD to form benzene and lithium or sodium hydride. In the case of lithium on the use of an equimolar amount of biphenyl, the isomerization of 1,4-CHD to cyclohexa-1,3-diene is also observed. When the molar ratio Li(Na): Ph2 increases from 1 : 1 to 2 : 1, i.e., when the reaction is carried out in the presence of an alkali metal solid phase, the overall conversion of 1,4-CHD into benzene and cyclohexene increases. The use of mixtures of lithium and sodium leads to acceleration of the processes of the formation of benzene and cyclohexene. The possible mechanism of the synergistic effect found is discussed.