Hydrodeoxygenation of aliphatic acid over NiFe intermetallic compounds: Insights into the mechanism via model compound study

[摘要] Hydrodeoxygenation (HDO) is a promising way to produce the second generation bio-diesel from aliphatic acid based biomass. Compared with the monometallic Ni/SiO2, appropriate introduction of Fe results in the complete conversion of lauric acid and nearly 100% yield of alkane as well as satisfactory stability on conversion. Further study on mechanism shows that the NiFe intermetallic compounds (IMC) catalyst promotes the ratedetermining step, i.e., C11H23COOH -> C11H23CHO, which is attributed to the synergistic effect of Ni-Fe bimetallic sites ac-cording to the characterization and calculation. For one thing, strong spin polarization enhances the interaction between Fe sites and aliphatic acid, and the subsequent dissociation of C-OH bond indicated by the DOS and transition state analysis. For another, dissociation of H-2 on Ni site is promoted because of the higher charge density around Ni in the IMC according to the in-suit FTIR and Bader analysis. However, with the repeated use of the catalyst, the selectivity to alkane decreased gradually, which is ascribed to the oxidation of metal Ni-Fe bimetallic sites. This demonstrates that the reduced Ni-Fe bimetallic sites rather than the oxidized ones are the active phases in the HDO of aliphatic acid to produce alkanes with the NiFe IMC.

[发布日期] 2021-12-01

[关键词] Intermetallic compound;Aliphatic acid;Hydrodeoxygenation;DFT;Ni-Fe catalyst