Investigation Into The Performance Of Hydrodeoxygenation Of Methyl Laurate On Bimetallic NiFe Catalyst

Silica supported Ni, Fe catalysts and FeNi bimetallic catalysts with different Fe/Ni weight ratios were prepared by the incipient wetness impregnation method. Chemical and physical properties of the catalysts and their precursors were characterized by N2 adsorption, H₂-TPR, XRD, TEM, H₂ chemisorption, ESR and TGA. The effects of Fe/Ni weight ratio and reaction condition?temperature, WHSV and H₂ pressure? on the performance of the catalysts in the deoxygenation of methyl laurate were evaluated on a fixed bed reactor. Together with the characterization results, the reason for the impact of Fe on the performance of Ni/SiO₂ was elucidated. It was found that the activity of Ni/SiO₂ was enhanced by addition of certain amount of Fe and it reached maximum at the Fe/Ni weight ratio of 1/4. The promotional effect was attributed to the synergism between Ni and Fe. The decarbonylation and hydrodeoxygeantion pathways mainly occurred on Ni/SiO₂ and Fe/SiO₂, respectively. Both routes took place on FeNi/SiO₂ and the increase of the Fe amount promoted the hydrodeoxygenation one. This was due to the oxophilicity of the Fe sites that favors to adsorb and activate the C=O and C-O bonds to give the hydrodeoxygenation products. The addition of Fe remarkably suppressed the C-C hydrogenolysis activity of Ni at high temperature, which was ascribed to the insertion of Fe that destroyed the ensemble of Ni sites which was essential to the hydrogenolysis of C-C bond. In addition, Ni/SiO₂ and NiFe/SiO₂?Fe/Ni weitht ratio of 1/4? had similar stability and were all deactivated. The Ni/SiO₂ deactivation was mainly attributed to the coking and the sintering of Ni particles, while the FeNi/SiO₂ deactivation mostly resulted from the coking.To further understand the influence of the the interaction between Fe and Ni on the catalyst performance, the effect of the reduction temperature on the structure and performace on 8 wt% Ni/Fe₂O₃ was investigated. The rise of reduction temperature reduced the deoxygenation activity of Ni/Fe₂O₃ and Fe₂O₃ because of the masking of Ni sites with Fe/FeOx speices, the decrease in the amount of active sites due to the sintering and the destruction of the synergism between metal sites and oxygen vacanncies. Reduction temperature did not significantly influence the deoxygenation routes of methyl laurate and the prevailling one was hydrodeoxygenation. Thus, both Fe and FeOx favored hydrodeoxygenation route. It was proposed that the synergism between the metallic Ni sites and the Fe sites?either in metallic or oxidation states? promoted the hydrodeoxygenation pathway when the NiFe alloy was formed.