Showing papers on "Ammonium tetrathiomolybdate published in 1996"

Synthesis of molybdenum disulphide by acidification of ammonium tetrathiomolybdate solutions

Abstract: Generally categorized in a large family of transition metal dichalcogenide layer crystals, molybdenum disulfide (MoS2) has been the subject of significant research interest for applications in non-aqueous lithium batteries [1], catalytic hydrodesulphurization of petroleum [2], and antiwear achievement by reduction in friction [3-5]. The successful application of this semiconductor compound originates largely from the sandwich interlayer structure, loosely bound by Van der Waals forces, evidenced by easy cleavage in the [0 0 1] direction along which the (S-Me-S) layers are stacked to form the crystal [6]. Apart from its natural state, known as molybdenite, crystalline MoS2 can also be synthesized by hightemperature solid state reaction between stoichiometrically mixed molybdenum and sulphur powders in vacuum [7-9], thermal decomposition of ammonium tetrathiomolybdate ((NH4)2MoS4) [10, 11] or amorphous molybdenum trisulfide (MoS3) [9, 12], and by thermally assisted transformation of amorphous MoS2 powders [13]. Synthetic MoS2 can also be prepared by sputtering [14], electrodeposition [15] and chemical deposition techniques [16]. The present letter reports formation of MoS2, by appropriate thermal treatment of precipitates resulting from acidification of ammonium tetrathiomolybdate solution. As mentioned previously, although MoS2 can be prepared from tetrathiomolybdate by thermal decomposition, the current work is of practical interest in that it produces evidence for in situ formation of MoS2 during anodizing of aluminium and its alloys in thiomolybdate electrolyte. Compared with the extensive research on the formation of alumina by anodizing, the formation of MoS2 during anodization has been rarely reported. Skeldon and Thompson [17] recently proposed to overcome the general poor surface retention of MoS2 by incorporating it, by anodizing, into a pre-anodized, hard porous alumina film on aluminium for tribological applications. The main anodic reaction during anodizing of aluminium results in proton generation at the pore base/electrolyte interface as follows

Reactions of Dibenzothiophene with Hydrogen in the Presence of Selected Molybdenum, Iron, and Cobalt Compounds

Abstract: The catalytic effects of several molybdenum-, cobalt-, and iron-containing compounds have been examined in the reactions of dibenzothiophene (DBT) with hydrogen under conditions related to coal liquefaction. The metal compounds are candidate catalyst precursors for direct coal liquefaction. The reactions were carried out in batch microautoclave reactors at 400 °C for 30 min with 6.9 MPa (cold) hydrogen pressure and tridecane solvent. A metal loading of 0.5 mol % resulted in low conversion and only hydrogenation. Addition of sulfur in a 4:1 molar ratio led only to a minor increase in conversion and hydrodesulfurization. The use of a higher boiling solvent (octadecane vs tridecane) was beneficial in providing increased conversion, hydrodesulfurization, and hydrogenation. An increase in metal compound loading to 36.2 mol % led to a dramatic increase in conversion, hydrodesulfurization, and hydrocracking. Molybdenum hexacarbonyl at 36 mol % loading, with added sulfur at 6:1 ratio and octadecane solvent, gave 100% conversion of dibenzothiophene to other products with 100% hydrodesulfurization. Ammonium tetrathiomolybdate and molybdenum(III) chloride are less active under similar conditions. A cobalt-molybdenum thiocubane complex gave unexpectedly low conversions. Iron and cobalt carbonyls also provided very low conversions, even with added sulfur.

Effect of Coal Characteristics and Molybdenum Sulfide Catalyst on Conversions and Yields of Heavy Products from Liquefaction in Phenanthrene

Abstract: Eight coals, ranging in rank from subbituminous B to high-volatile A bituminous, were reacted in microautoclave reactors in a hydrogen atmosphere and with the nondonor solvent phenanthrene. Reactions were conducted at 360 °C for 1 h. Both noncatalytic and catalytic reactions were investigated. The catalytic reactions employed ammonium tetrathiomolybdate as a catalyst precursor. In noncatalytic reactions, conversions ranged from 18 to 47% and showed a dependence on the oxygen contents of the coals. Addition of a catalyst increases conversions to 54−83%. In catalytic reactions there is no apparent dependence of conversion on oxygen content, but rather the hydrogen content, the net hydrogen (the total hydrogen corrected for oxygen, sulfur, and nitrogen), and its distribution in the coal structure are important. Segregation of the coals into groups originally defined by Given shows two different effects of added catalyst: for medium- to low-rank medium-sulfur coals the available hydrogen in the coal and that...