Fischer–Tropsch Synthesis: Using Deuterium as a Tool to Investigate Primary Product Distribution Jia Yang • Wilson D. Shafer • Venkat Ramana Rao Pendyala • Gary Jacobs • De Chen • Anders Holmen • Burtron H. Davis Received: 6 September 2013 / Accepted: 12 November 2013 / Published online: 17 December 2013 Ó Springer Science+Business Media New York 2013 Abstract Accumulation of products is a known phe- nomenon associated with a continuously stirred tank reactor (CSTR). Secondary reactions of a-olefins due to prolonged bed/pore residence time can significantly change the primary Fischer–Tropsch product distribution. Using D 2 as a tracer, this study first investigated the significance of Fischer–Tropsch product accumulation in a CSTR. Secondly, the D 2 tracer study was used to investigate pri- mary product distribution and olefin to paraffin ratios. Based on the D 2 study, it was found that Fischer–Tropsch synthesis with a 2.5 % Ru/NaY catalyst follows a single a mechanism with a chain growth probability of about 0.74. Both olefins and paraffins are primary products and the ruthenium catalyst produced a similar olefin/paraffin ratio for each carbon number. The apparent decline of the O/P ratio for higher carbon number products was shown to be due to secondary reactions of the olefin at prolonged resi- dence times. D 2 tracing was shown to be a versatile tool to investigate product accumulation and to define primary product distribution which is very important for mecha- nistic interpretation and kinetic modeling. Keywords Fischer–Tropsch synthesis  Deuterium  Primary product distribution  Olefin/paraffin ratio  H 2 –D 2 switching 1 Introduction Fischer–Tropsch synthesis (FTS) is a polymerization reaction that produces a wide variety of products, including paraffins, olefins and oxygenates. The simple polymeriza- tion model that was applied to describe FTS products by Anderson et al. [1] had been developed independently in another context by Schulz [2] and Flory [3]. Therefore, the polymerization model for polymerization is usually refer- red to as the Schulz–Flory distribution but for FTS it is usually considered as an Anderson–Schulz–Flory (ASF) plot. FTS products that follow an ideal ASF distribution can be described by the following equation: W n n ¼ð1  aÞ 2 a n1 where W n /n is the mole fraction of hydrocarbons with carbon number n and a is the chain growth probability. A semilogarithmic plot of mole fraction of the FTS products as a function of carbon number should give a straight line. However, many studies have shown that the measured product distribution does not obey ASF kinetics, especially when the carbon number of the hydrocarbons is [ C 8 –C 14 [4–6]. Both positive [5–10] and negative deviations [11– 15] from the ASF distribution have been reported. Deviations from an ideal ASF plot have been explained by different theories, including: two types of reaction centers/sites with two chain or more growth probabilities [5–7, 9, 10, 16, 17]; diffusion enhanced reincorporation of higher olefins [18– 20]; olefin readsorption due to greater physisorption strength or greater solubility [21–23]; vapor–liquid equilibrium (VLE) phenomena [24, 25]; chain-length dependent product accu- mulation [11, 13, 15]; a gradient in the process conditions at the particle or reactor scale [26]; and chain length dependent olefin desorption or greater olefin adsorptivity [27–29]. J. Yang  D. Chen  A. Holmen Norwegian University of Science and Technology, 7491 Trondheim, Norway J. Yang  W. D. Shafer  V. R. R. Pendyala  G. Jacobs  B. H. Davis (&) Center for Applied Energy Research, University of Kentucky, 2540 Research Park Dr., Lexington, KY 40511, USA e-mail: burtron.davis@uky.edu 123 Catal Lett (2014) 144:524–530 DOI 10.1007/s10562-013-1164-6