Studies On Selective Hydrogenation Of Esters Over Cu-based Catalysts

Due to the shortage of petroleum resources,the hydrogenation of esters（which were produced through C1-route and biomass conversion route）to alcohol compounds has important economic and environmental values.Carbonates and acetates are typical carboxylic acid esters.The studies on the catalytic hydrogenation of carbonates and acetates can provide theoretical guidance for the hydrogenation of other esters.In this thesis,the esters such as ethylene carbonate（EC）and cyclohexyl acetate（CA）were applied as model reactants to study the selective hydrogenation over Cu-based catalysts.There are maily two parts:In the first part,the Cu/SiO₂ catalysts with a 20.0 wt%Cu loading were prepared via different methods and applied to the chemoselective hydrogenation of EC to yield ethylene glycol（EG）and methanol（ME）.The results showed that the Cu/SiO₂-AE catalyst prepared by an ammonia evaporation（AE）method was superior to the Cu/SiO₂-DP prepared by the deposition-precipitation（DP）method.Because of the pore-forming function of glucose,the removal of glucose from the catalyst precursor during the calcination process would have a certain effect on the structure of the catalyst.To improve the catalytic performance,the Cu_xG₁/SiO₂-AE catalysts were also prepared via a modified AE method.After further modification using glucose with optimal amount,the Cu₈G₁/SiO₂-AE catalyst showed enhanced catalytic performance,furnishing 86%selectivity to ME and 99%selectivity to EG at almost full conversion of EC,TOF for ME formation reaching about 38.7 h^-1.In addition,the Cu₈G₁/SiO₂-AE catalyst also possessed better stability.Based on detailed characterization results,it was found that the Cu/SiO₂ catalyst prepared by AE had a smaller Cu particle size than which prepared by DP.After modification with glucose,the Cu₈G₁/SiO₂-AE catalyst had the smallest Cu particle size,largest hydrogen adsorption ability,and the strongest interaction of Cu with SiO₂ so that the highest Cu⁺/（Cu⁰+Cu⁺）molar ratio was detected.Therefore,the Cu₈G₁/SiO₂-AE catalyst obtained the best reaction result under the same conditions.In the second part,the binary Cu₁Al₁,Cu₁Mn₁ and the ternary Cu_xAl₁Mn_2-x-x catalysts were prepared via a DP method for the chemoselective hydrogenation of CA to yield ethanol and cyclohexanol simultaneously.The results show that the ternary Cu_xAl₁Mn_2-x catalysts exhibited superior behaviors when compared with the binary Cu₁Al₁ and Cu₁Mn₁ catalysts.Among the Cu_xAl₁Mn_2-x catalysts with different Cu/Mn molar ratios,the Cu₁Al₁Mn₁ catalyst exhibited the enhanced catalytic performance,furnishing 95.0%EC conversion and 97.6%selectivity to ethanol along with 93.6%selectivity to cyclohexanol at 2.0 h in a batch reactor,and also furnished an excellent stability in a fixed-bed reactor.According to the detailed characterization results,the ternary Cu₁Al₁Mn₁ catalysts possessed relative more uniform Cu particle dispersion,less aggregation and much larger BET specific surface area than those of the binary Cu₁Al₁ and Cu₁Mn₁ catalysts.Furthermore,the Cu₁Al₁Mn₁ catalyst possessed the largest Cu⁰/（Cu⁰+Cu⁺）molar ratio and the highest Oβ/O_T molar ratio,which played important roles in the hydrogenation of CA including the adsorption of hydrogen and ester molecules with following activation of carbonyl groups.