Hydrodeoxygenation Of Sebacic Acid Catalyzed By Titania-Supported Ruthenium

As a bio-derived platform molecule,levulinic acid can be converted to liquid fuels with similar components to aviation kerosene after undergoing aldol self-condensation and hydrodeoxygenation（HDO）reactions.In view of the complicated structure and composition of levulinic acid self-condensation products,sebacic acid was selected as a model compound for the products in this work.We hope the investigation of the HDO performance of sebacic acid will help intensive understanding of the HDO of levulinic acid self-condensation products.Firstly,the effects of different metal active components（Ni,Co,Cu,Pd,Pt,Ru）and supports（TiO₂,SiO₂,γ-Al₂O₃,H-ZSM-5,ZrO₂,AC）on the catalytic performance were studied and the best catalyst Ru/TiO₂was screened out.NH₃-TPD and CO₂-TPD measurement results showed that the catalyst with a larger amount of base sites is more conducive to the conversion of sebacic acid while the proportion and distribution of acid-base sites affected the selectivity of HDO products.The number of acid sites of catalyst should be greater than the base sites,and the suitable ratio of the number of acid sites to that of base sites is 1.6:1.In the suitable catalyst,three kinds of acid sites with strong,medium,and weak strength should exist simultaneously,and furthermore,the quantity distribution follows the order:medium acid sites>strong acid sites>weak acid sites.Moreover,three kinds of base sites with strong,medium,and weak strength should also exist simultaneously,and furthermore,the quantity distribution follows the order:medium base sites>weak base sites>strong base sites.The influences of preparation conditions on the catalytic performance of Ru/TiO₂were investigated and its appropriate preparation conditions were obtained as follows:a Ru loading of 5 wt.%,a reduction temperature of350℃,a reduction time of 4 h,and a reduction atmosphere of V_H2:V_N2=60:40.Combined with catalyst characterization such as XRD,TEM,XPS,and CO pulse chemisorption,it was found that the excellent catalytic performance of Ru/TiO₂is also attributed to a moderate degree of Ru reduction and dispersion.The suitable reaction conditions for Ru/TiO₂-catalyzed HDO reaction of sebacic acid were obtained as follows:a catalyst dosage of 40 mg,a reaction temperature of 210℃,a hydrogen pressure of 4 MPa,a reaction time of 5 h,a reaction atmosphere of H₂and a solvent of n-heptane.In this case,the conversion of sebacic acid was 100%,the selectivity of C₈,C₉,and C₁₀alkanes were70.6%,23.5%,and 2.7%,respectively.Based on GC-MS analysis,some possible reactions in the Ru/TiO₂-catalyzed sebacic acid HDO process were speculated and the reaction network was established.After four repeated experiments,the conversion of sebacic acid and the selectivity to C₁₀alkane of Ru/TiO₂did not change significantly while the selectivity of C₈and C₉alkanes decreased by 6.6%and 1.1%,respectively,which may be due to the loss of Ru metal in Ru/TiO₂catalyst during the reaction.Then the effect of metal oxide promoters MoO_x,WO_x,ReO_x,VO_x,and Nb O_xon the catalytic performance of Ru/TiO₂was investigated and it was found that Ru-ReO_x/TiO₂showed high HDO catalytic performance at a mass ratio Ru/Re of 5:5.NH₃-TPD characterization results showed that the addition of promoter affects the acidity of the catalyst.When the catalyst has more acid sites and the proportion of weak,medium,and strong acid sites is about 4.0:10:1.0,the catalytic activity is higher.Through XPS,NH₃-TPD,BET,and TEM characterizations,we found that the addition of ReO_xcaused the following results:（1）promoted the interaction between Ru and ReO_x;（2）provided acid sites on the surface of the catalyst,and the weak and medium acid sites on the catalyst surface affected the selectivity of HDO products;（3）improved the stability of metal Ru at high temperatures and promoted the dispersion of active components.The suitable reaction conditions for 5Ru-5ReO_x/TiO₂-catalyzed HDO reaction of sebacic acid were obtained as follows:a catalyst dosage of 50 mg,a reaction temperature of 210℃,a hydrogen pressure of 6 MPa,and a reaction time of 5 h.Under the above conditions,the conversion of sebacic acid was 99.9%,the selectivity of C₈,C₉,and C₁₀alkanes were 38.1%,43.8%,and 11.8%,respectively.Compared with Ru/TiO₂,Ru-ReO_x/TiO₂increased the selectivity of C₉and C₁₀alkanes（products from partial or complete HDO reaction of sebacic acid）by 20.3%and 9.1%,respectively.5Ru-5ReO_x/TiO₂did not change significantly in the conversion of sebacic acid and the selectivity of C₁₀alkane after four repeated experiments.However,the selectivity of C₈and C₉alkanes respectively decreased by 4.0%and 1.6%,possibly due to the leaching of metal Ru during the reaction.