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Novel aspects of the physical chemistry of Co/SiO2 Fischer–Tropsch catalyst preparations: The chemistry of cobalt silicate formation during catalyst preparation or hydrogenation

Paper ID Volume ID Publish Year Pages File Format Full-Text
44658 46050 2006 9 PDF Available
Title
Novel aspects of the physical chemistry of Co/SiO2 Fischer–Tropsch catalyst preparations: The chemistry of cobalt silicate formation during catalyst preparation or hydrogenation
Abstract

Co/SiO2 catalysts were prepared by both impregnation and precipitation techniques and analyzed by IR, TPR, XRD, and BET methods at intermediate stages of their preparation to define the stage and mechanism of cobalt silicate formation. To prove that reducing conditions can lead to cobalt silicate, one part of a catalyst prepared by impregnation of silica with cobalt nitrate was calcined in air at 350 °C, and another part in H2–N2 atmosphere at the same temperature. Infrared spectra revealed the presence of Co–O–Si absorption in the sample exposed to reducing atmosphere. Cobalt silicate formation is postulated to be a reaction between migrating silicic acid and hydrated cobalt hydroxide generated in the reduction process.Precipitation of cobalt nitrate solution at 80–90 °C with potassium hydroxide solution in the presence of Davison 952 silica resulted in amorphous cobalt silicate formation. Precipitation with sodium carbonate solution gave no IR-detectable quantities of cobalt silicate in the presence of Davison 952 silica, but cobalt silicate was detected when Cab-O-Sil HS-5 silica was used. Precipitations of Co and Mg nitrates (∼2:1 Co/Mg ratio) with sodium carbonate gave essentially quantitative yield of amorphous cobalt silicates whether the precipitation occurred in the presence of Davison 952 silica, or the silica was added after the precipitation. Cobalt silicate formation during precipitation either by KOH or Na2CO3 solutions is a heretofore unrecognized facile reaction of hydrated cobalt hydroxide with silicic acid (dissolved silica). The mechanism which can explain Co(OH)2(H2O)x formation during Na2CO3 precipitations is an acid–base reaction between hydrated Co ions and carbonate ions. This reaction also yields carbonic acid, which competes with silicic acid for Co(OH)2(H2O)x in secondary reactions.

Keywords
Fischer–Tropsch; Cobalt; Silica; Cobalt silicate
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Novel aspects of the physical chemistry of Co/SiO2 Fischer–Tropsch catalyst preparations: The chemistry of cobalt silicate formation during catalyst preparation or hydrogenation
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 311, 1 September 2006, Pages 146–154
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
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Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
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