Tungstate, impregnation with

Imidazole derivatives 380 Imperatorin 65 Impregnation of TLC layers 86 -with caffeine 86 -with silver nitrate 86 -with tungstate 86 Indeno(l,2,3-cd)pyrene 39,85 Indicators, pH- 303 -, reagents 45 Indium cations 144 Indoleacetic acid 45... 

Association of molybdates (tungstates) with phosphate-like structures leads to a class of compounds called heteropoly compounds or heteropoly acids of Mo or W, hereafter schematically written as Mo —P or W—P heteropoly compounds. The heteropoly anions, which may contain Mo, W, P, and other elements, are paired, both in the solid state and in solution, with cations such as H+, NH4, and Na+. Here, only some Mo —P heteropoly compounds playing an important role in hydrotreating catalysts during the catalyst preparation (impregnation) or as supported oxidic phases are discussed. The Mo — P heteropoly compounds have the following properties 18,19) ... 

Usually WOj/Zr02 catalysts are synthesized by co-precipitation of zirconium and tungsten hydroxides or by impregnation of dried zirconium hydroxide with ammonium meta-tungstate solution with subsequent calcining of samples at 700-800°C [1-6]. However the samples so obtained possess relatively low surface area (40-60 m /g). 

A catalyst was prepared by impregnating a sample of alumina with a solution of sodium tungstate and mixing with the aid of ultrasonic agitation. The sample was dried in a vacuum dessicator ( 4 hour) and in air at 90°C (1 hour). Concentrated nitric acid (10 mL) was added and the beaker warmed on a hot plate for 5 minutes and the solid was then washed with 1M nitric acid by decantation. To remove sodium nitrate, 1M nitric acid (250 mL) was added, the catalyst digested for 1 hour on a hot plate and the nitric acid decanted. This washing was repeated three times and the catalyst dried at 150-160°C. 

A marked improvement in separation is less frequently achieved with other complex-forming salts like sodium arsenite, tungstate, molybdate or metavanadate or basic lead acetate. Boric acid or borax are more often employed as impregnation agents for complex-formation. Mobeis [317 a] and Schorn [615 a] have undertaken good compilations of the results so far obtained in this field. 

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