A Density Functional Theory Study on Acetic Acid Decomposition on Ni(111)

摘要

Catalytic steam reforming of bio-oil is a potential process to convert renewable biomass feedstocks into hydrogen. However, carbon deposition on the catalyst is the major problem encountered in the steam reforming process. To shed light on the coke formation mechanism, acetic acid (CH_3COOH), the smallest organic molecule that contains C-O, C-C, C-H, O-H and C=0 bonds, is selected as the model compound of the oxygenates in bio-oil. Thus, density functional theory is applied to investigate the decomposition mechanism of acetic acid on the Ni (111) surface. To gain a good knowledge of the high selectivity towards hydrogen and a comprehensive interpretation of coke formation mechanism, all of the possible decomposition pathways of acetic acid are considered, especially for the dehydrogenation pathways and C-C bond scission reactions. The stable adsorption geometry configuration and adsorption energies of different species and the important intermediates are determined. Based on our calculations, the most favorable decomposition pathway on Ni (111) surface is CH_3COOH*→CH_3COO*→CH_3CO*→CH_2CO*→CH_2*→CH*, and the decomposition of acetyl (CH_3CO*) via C-H bond cleavage to form CH_2CO is the rate-determining step with a high activation barrier of 1.33 eV. Meanwhile, the carbon deposits formation results from the accumulation of CH* species, which is mostly from the dehydrogenation of CH_2*. Moreover, the formation pathways and initial dissociation of acetone intermediates is also investigated.