A mechanistic study of the fischer-Tropsch synthesis using transient isotopic tracing.Part 2:Mode quantification

摘要

A quanttative mehcanistic modle for the low-pressure Fischer-Tropsch synthesis reaction on a Co/Ru/TiO_2 catalyst is presented.Although the Fischer-Tropsch synthesis is operated at dry conditions,the presence of a physisorbed state is essential in the mechanism.The monolayer ocverage of the C_3 to C_20 hydrocarbons in the physisorbed state is low at 0.3%.The most abundant chemisorbed surface species are CO_ads and two single-C species,C_alpha,ads and C_beta,ads.The fractional surface coverage of growing hydrocarbon chains is low at1.4%.With increasing H_2/CO feed ratio,the surface concentrations of H_ads and free sites increase.The rate coefficient for chain initiation is one order of magnitude lower than that for chain growth.The rate coefficient of ethene readsorption is one order of magnitude highe rthan that fo rthe readsorption of higher 1-olefins.Chain branching and bond shift and thus decreasing the asymptotic chain growth probability.As is to be expected,the termination to paraffin is represented by a hydrogenation reaction.The growin hydrocarbon chain is hterfoe represented by a C_iH_2i speices.The quantitative mechanistic model as presented in this paper in combination with additional assumptions is used to successfully predict the characteristics of the product distribution o fthe high-pressure Fischer-Tropsch reaction.