Complex tellurium oxides

Catalysts. In industrial practice the composition of catalysts are usuaUy very complex. Tellurium is used in catalysts as a promoter or stmctural component (84). The catalysts are used to promote such diverse reactions as oxidation, ammoxidation, hydrogenation, dehydrogenation, halogenation, dehalogenation, and phenol condensation (85—87). Tellurium is added as a passivation promoter to nickel, iron, and vanadium catalysts. A cerium teUurium molybdate catalyst has successfliUy been used in a commercial operation for the ammoxidation of propylene to acrylonitrile (88). 

Test of Uptake Model Based on a Slow Surface Reaction Combined with Diffusion within the Particle. Since the simple diffusion model is inadequate to describe the uptake behavior of the molybdenum and tellurium oxide vapors by the clay loam particles, a more complex model is required, in which the effects of a slow surface reaction and of diffusion of the condensed vapor into the particle are combined. Consider the condensation of a vapor at the surface of a substrate (of any geometry) and the passage by diffusion of the condensed vapor through a thin surface layer into the body of the substrate. The change in concentration of solute per unit volume in the surface layer caused by vapor condensa-... 

The same complexes were isolated when a mixture of diaryl tellurium oxide, a slight excess of 70% perchloric acid, and the ligand was refluxed for 10 h1. 

Diphenyl tellurium oxide and metal halides reacted in ethanol at 5° to produce coordination compounds with two or three diphenyl tellurium oxide ligands per metal atom. The complexes were recrystallized from ethanol5. 

Halides of aluminum, silicon, and phosphorus5, tin tetrachloride, titanium tetrachloride, and antimony pentachloride6 did not form complexes with diphenyl tellurium oxide, but converted it to the corresponding diphenyl tellurium dihalide. 

The complex solid state relations of the cerium-molybdenum- tellurium oxide system were studied to determine the boundaries of single phase regions and phase distributions of a typical multicomponent ammoxidation catalyst. Between 400 and 600 C in air the (Ce,Mo,Te)0 system contains the following phases ... 

The electrodeposition of copper indium selenide and telluride was discussed by Bhattacharya and Rajeshwar (66). The deposition solutions were made in a multistep process. A 0.5 M solution (A) of indium chloride was prepared. The copper solution (B) was prepared from cuprous chloride dissolved in 30 ml of triethanolamine, 40 ml of 30% ammonia and 150 ml of water. The copper concentration was 0.5 M. Solutions A and B were mixed in equal amounts, diluted 10 times and adjusted to pH 1 with HCI. This solution (C) was aged for 24 hrs. The actual deposition bath was made from 20 ml of either 0.1 M selenium oxide or 0.1 M tellurium oxide and 60 ml of solution C. The triethanolamine was added to the copper solution as a complexing agent to shift the deposition potential. Depositions were carried out at -1.0 volt versus a saturated calomel electrode. The initial current density was 12 mA/cm . 

Early catalysts for acrolein synthesis were based on cuprous oxide and other heavy metal oxides deposited on inert siHca or alumina supports (39). Later, catalysts more selective for the oxidation of propylene to acrolein and acrolein to acryHc acid were prepared from bismuth, cobalt, kon, nickel, tin salts, and molybdic, molybdic phosphoric, and molybdic siHcic acids. Preferred second-stage catalysts generally are complex oxides containing molybdenum and vanadium. Other components, such as tungsten, copper, tellurium, and arsenic oxides, have been incorporated to increase low temperature activity and productivity (39,45,46). 

The solution should be free from the following, which either interfere or lead to an unsatisfactory deposit silver, mercury, bismuth, selenium, tellurium, arsenic, antimony, tin, molybdenum, gold and the platinum metals, thiocyanate, chloride, oxidising agents such as oxides of nitrogen, or excessive amounts of iron(III), nitrate or nitric acid. Chloride ion is avoided because Cu( I) is stabilised as a chloro-complex and remains in solution to be re-oxidised at the anode unless hydrazinium chloride is added as depolariser. 

N,N -Chelation is also exhibited by the dianionic P(III)/P(V) ligands (25) in the MejSn complex (31) [39] and in the magnesium complex (32) [40], which is prepared by oxidation of [Mg(thf)2[ BuNP(p-N Bu)2PN Bu] by elemental tellurium [40]. One of the endocychc N Bu groups in (32) is also weakly coordinated to magnesium, thus providing an intramolecular base-stabihzation similar to that observed for complexes of type (8). 

The mechanism of tellurium resistance has been investigated using genetic manipulation similar to that of Se (see above) and cellular oxidant capacity apparently plays an important role.144,206 A few tellurite determinants - both chromosomal and plasmid encoded - have been identified in bacte-ria.113,147 192 207 208 Recent studies have focused on the role of methyltransf-erases in Te resistance. Liu et a/.111 determined that the E. coli gene tehB uses S-adenosyl methionine and a methyltransferase in tellurite detoxification, but while no methylated tellurium compounds (see below) were observed, a loss of tellurite was observed in tellurite-amended cultures and Te complexation was inferred.191... 

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