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Effect of chlorine on the selectivity of a fischer‐tropsch catalyst composed of iron/vanadium oxides
Author(s) -
Jacobs Jochen,
Baerns Manfred
Publication year - 1988
Publication title -
chemical engineering and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.403
H-Index - 81
eISSN - 1521-4125
pISSN - 0930-7516
DOI - 10.1002/ceat.270110106
Subject(s) - catalysis , fischer–tropsch process , selectivity , chemistry , isomerization , chlorine , olefin fiber , inorganic chemistry , adsorption , dissociation (chemistry) , vanadium , product distribution , organic chemistry
Fischer‐Tropsch catalysts (Fe/V oxides with ZnO and K 2 CO 3 as promoters) were exposed to CHCl 3 , thereby producing surface and bulk chlorides. The effect of this exposure on activity and selectivity was studied in a continuous recycle reactor at a total pressure of 10 bar (CO/H 2 in most experiments: ca 1:1) in a temperature range between 200 and 343°C. CHCl 3 was introduced in amounts of up to 1 × 10 −2 mol chlorine per g catalyst. The catalyst samples were characterized by internal surface area, pore‐size distribution and adsorption capacities for CO, H 2 and C 2 H 4 . Prior to synthesis, the catalysts were reduced by H 2 . Catalyst exposure to CHCl 3 resulted in a decrease of activity and considerable changes in product distribution. Hydrogenation and isomerization of 1 ‐olefins were partly suppressed; the chain length of the products was slightly increased. Deactivation of the catalysts due to chlorine addition was partly reversible during operation, while olefin formation was not significantly altered with time‐on‐stream. The effect of chlorine on activity and selectivity is explained by dissociation of CO as the chain initiating step and CO insertion into a carbon/metal bond as a possible chain propagation step. Since adsorption capacity for H 2 decreases on the addition of chlorine, this may also contribute to lower activity and change in selectivity, compared to the unexposed catalyst.