Preparation And Tuning Of Copper-Based Catalysts For Hydrogenation Of Fatty Esters In Condensed Phase

Fatty alcohol is an important industrial intermediate for the production of detergents,surface active agents,cosmetics,textiles,lubricant and industrial solvents.Bio-oil as raw material to produce natural fatty alcohols is green and sustainable.Currently,natural fatty alcohols are mainly produced by hydrogenation of esters obtained by transesterification between fats and methanol or fatty acids obtained by hydrolysis of fats.For fatty esters with long carbon chains,the condensed phase reaction is more economical because of the low energy consumption.However,it is challenging to maintain the superior activity and stability in the hydrogenation of fatty esters in condensed phase.In this work,the mesoporous carbon nanocages Cu-xSi@C catalysts were prepared by ammonia evaporation（AE）,and its catalytic performance and the structure-activity relationship in condensed esters hydrogenation were studied.Using silica sol as the silica source and phenolic resin as the carbon source,a series of composite support with different silica contents were synthesized.Then,the Cu/SiO₂catalysts confined in mesoporous carbon nanocages were prepared by different method.Compared with deposition precipitation（DP）and impregnation（IM）method,the ammonia evaporation（AE）method promoted the dispersion of active species and exhibited higher hydrogenation activity.The effect of silica content on the physicochemical properties and catalytic performance of the catalyst in esters hydrogenation were investigated.Transmission electron microscopy（TEM）and infrared spectroscopy（FTIR）results confirmed the existence of phyllosilicates.Combined with X-ray diffraction（XRD）,the role of silica in promoting the dispersion of copper species was demonstrated.The effect of silica content in adjusting the copper valence state was illustrated by X-ray photoelectron spectroscopy（XPS）results.When the silica content was 56%,the catalyst presented the minimum copper nanoparticle size and the best Cu⁺/Cu⁰ ratio,leading to the highest yield of fatty alcohol.The STY of lauryl alcohol had a good linear relationship with the surface area of Cu⁺,indicating that the Cu⁰ site in the catalyst is sufficient for the activation of hydrogen,and the dissociative adsorption of the carbonyl group became the controlling step of the reaction.In addition,the thermal stability and methanol resistance of Cu-56Si@C catalyst were tested.After high-temperature thermal shock（450℃）,Cu-56Si@C catalyst still maintained a relatively stable catalytic activity.The spatial confinement of mesoporous carbon nanocage structure effectively restrained the agglomeration of copper particles encapsulated inside.In the environment of high temperature and methanol solvent,Cu-56Si@C catalyst exhibited superior stability with less metal loss and negligible aggregation of copper nanoparticles.On basis of the Density functional theory（DFT）simulation results,it was confirmed that methanol had etching effect on hydroxylated silica,leading to the deactivation of the catalyst.While less hydroxyl on the silica surface would promote the stability of Cu-Si@C catalyst in methanol environment.