Acetylenes as probes in the Fischer–Tropsch Reaction

Abstract

Long-chain acetylenic molecules (from C6 to C10) have been added as probe molecules to the synthesis gas feed in FischerTropsch(FT) reactions on Co/Al 2 O 3 at 0.7 Mpa and 150-220°C. The acetylenic molecules initiated the reaction at temperatures as low as 150°C. Use of a phenyl-substituted acetylene allowed the FT products initiated by the alkyne to be distinguished from base case FT synthesis. Terminal alkynes produced straight chain products while internal alkynes produced both terminal and internal products. Aldehydes and alcohols with one carbon more than the added acetylenic probe molecule were the only oxygenates formed, perhaps by a hydroformylation type of reaction.

Addition of Acetylene to the Fischer−Tropsch Reaction

“…There is a marked difference between iron and cobalt catalysts in the distribution of oxygenates in the F−T synthesis . With cobalt, the addition of substituted acetylenes such as 1-hexyne or phenylacetylene yields oxygenates formed by the addition of a single carbon; e.g., 1-hexyne yields only heptaldehyde or 1-heptanol, evidently by the hydroformylation of 1-hexene …”

“…Work with 14 C labeled acetylene showed that acetylene is incorporated only once in the growing chain . Our previous work with phenyl-substituted acetylenes showed that alkynes initiate chain growth, forming the first two carbons of the growing chain . When acetylene is added to the F−T reaction at 220 °C, two products are formed: about half of the chains are initiated by acetylene; the other half do not contain acetylene (the normal F−T reaction takes place).…”

“…Supported cobalt catalysts were prepared by incipient wetness impregnation of cobalt nitrate on a spray-dried alumina (70−140 mesh) as described elsewhere . The catalyst composition is 10 wt % Co on an alumina support (10Co/90Al 2 O 3 ).…”

“…Previous work on the incorporation of substituted alkynes such as 1- and 2-hexyne and phenylacetylene to the F−T synthesis has shown that addition of these molecules to cobalt- and iron-catalyzed F−T reactions allows the synthesis to proceed at lower-than-normal F−T temperatures . Alkynes serve only as chain initiators; they are not incorporated further in the F−T chain.…”

Coupling vs Surface-Etching Reactions of Alkyl Halides on GaAs(100). 2. CH2I2 Reactions

“…One such process is Fischer−Tropsch (FT) synthesis of long-chain hydrocarbons for clean transportation fuels from CO/H 2 mixtures, the reaction being catalyzed by cobalt-, ruthenium-, and nickel-based catalysts. A problem with FT synthesis is a lack of product selectivity, with C 1 to >C 100 alkenes, alkanes, and oxygenates being formed, and hence there has been a recent surge in investigations aimed at catalyst screening and mechanistic studies to develop highly selective catalysts for achieving a specific product distribution. − Numerous surface investigations (see for example reviews by Zaera and Bent on the subject) of alkyl reactions on transition metals have been conducted under ultrahigh-vacuum conditions to further understand the carbon−carbon bond formation. Surface alkyl species are particularly useful in these investigations because they can be easily generated on surfaces from alkyl halides, especially alkyl iodides with a relatively weak C−I bond, and direct coupling of the alkyl occurs to yield the corresponding higher alkane in the majority of cases.…”