Understanding the Effect of Cobalt Particle Size on Fischer-Tropsch Synthesis: Surface Species and Mechanistic Studies by SSITKA and Kinetic Isotope Effect

作者：Yang Jia; Tveten Erik Z; Chen De; Holmen Anders^*

来源：Langmuir, 2010, 26(21): 16558-16567.

DOI：10.1021/la101555u

Co/gamma-Al(2)O(3) catalysts with particle sizes in the range of 4-15 nm were investigated by isothermal hydrogenation (IH), temperature programmed hydrogenation (TPH), and steady-state isotopic transient kinetic analysis (SSITKA). Kinetic isotope effect experiments were used to probe possible mechanisms on Co/gamma-Al(2)O(3) with different particle size. It was found that CO dissociated on Co/gamma-Al(2)O(3) catalysts at 210 degrees C. The total amount of CO(2) formed following the dissociation depends on the cobalt crystal size. O-Co binding energy was found lobe highly dependent on the Co metal particle size, whereas similar C-Co binding energy was found on catalysts with different Co particle size. Very strongly bonded carbon and oxygen surface species increased with decreasing particle size and acted as site blocking species in the methanation reaction. SSITKA experiments showed that the intrinsic activity (1/tau(CHx)) remained constant as the particle size increased from 4 to 15 nm. The number of surface intermediates (N(CHx)) increased with increasing particle size. The apparent activation energies were found similar for these catalysts, about 85 kJ/mol. D(2)-H(2) switches further confirmed that the particle size did not change the kinetically relevant steps in the reaction. The reactivity of the active sites on the 4 nm particles was the same as those on the 8, 11, and 15 nm particles, and only the number of total available surface active sites was less on the 4 nm particles than on the others.

• 出版日期2010-11-2