Fischer-Tropsch Synthesis: Deuterium Kinetic Isotopic Effect for a 2.5 % Ru/NaY Catalyst

摘要

The isotopic effect of D2 was investigated for a 2.5 % Ru/NaY catalyst for Fischer-Tropsch synthesis at industrially relevant conditions (493 K, 1.92 MPa, H2/ CO = 2). An inverse kinetic isotopic effect was found for CO conversion (r_D/r_H = 1-1.4) and methane formation (1.2-1.4), suggesting that H is involved in the rate determining steps of both reactions. D2 enhanced methane formation and inhibited C_(2+) formation and therefore decreased chain growth probability. The decline in r_D/r_H with carbon number is due to increasing dependence on the ratio (<1) of the chain growth probability. D2 also favored paraffin formation over olefins. The apparent activation energy for methane formation was higher with H2 (116 kJ/ mol) than with D2 (98 kJ/mol). The inverse kinetic isotopic effect arises from a combination of the kinetic isotopic effect of the rate limiting step and the thermodynamic isotopic effect of the equilibrium constant. The activity and product selectivity is consistent with a higher surface D coverage relative to H.