Catalytic Activity And Mechanism Study Of Hvdrogenation Of Levulinic Acid And Decarboxylation Of Fatty Acid Over Re-Based Catalyst

With the development of quantum mechanics theory,density functional theory calculation has been able to calculate some chemical structures in the field of computational chemistry and consistent with experimental data.It also can predict chemical reaction result in some respects.In the current metal catalyst research,various characterization methods are used to determine the physicochemical properties and morphological characteristics of the catalyst,which can explain the catalytic effect of the catalyst and catalytic mechanism.However,it cann't be able to explain the electron transfer and structural changes between the catalyst and the reaction substrate at the atomic level.On the one hand,computational chemistry can verify experimental data,explain experimental phenomena from the microscopic level.On the other hand,it can predict experimental phenomena by calculating data such as adsorption energy,reaction energy barrier,and vibration frequency,which can replace the chemical experiments.Here,we prepared two kinds of bimetallic catalysts by incipient wetness impregnation method to catalyze the reactions of levulinic acid to ?-valerolactone and oleic acid to long-chain alkanes.And the excellent catalytic performance of bimetallic catalysts by density functional theory calculation was interpreted.Firstly,Co-Re bimetallic catalyst was prepared for the hydrogenation of levulinic acid to prepare y-valerolactone.The results showed that levulinic acid could be completely converted by using 1 wt%Co0.5-Re0.5/TiO2 catalyst and reacting with 1,4-dioxane as solvent at 180? and 1.5 MPa H2 for 4 h.The yield of ?-valerolactone was 99.3%.According to XPS analysis,Co was present in elemental form,and Re was present in the form of ReO2.The adsorption energy of levulinic acid and hydrogen atoms on Co and ReO2 crystal faces and the dissociation energy of hydrogen molecules on the two crystal faces were calculated by density functional theory.The levulinic acid and hydrogen atom are more likely to adsorb on the surface of ReO2,and the adsorption energies are-0.878 eV and-0.725 eV respectively.Hydrogen molecule is more likely to dissociation on the Co crystal face with a dissociation energy of 0.038 eV.Combined with the experimental data,the better catalytic activity of the catalyst is attributed to the strong selective adsorption capacity of ReO2 for hydrogen atoms and levulinic acid.And the efficient dissociation performance of Co on hydrogen molecules.Based on the above work,we further investigated the effects of other hydrogen donors(methanol,isopropanol,formic acid,formaldehyde,hydrazine hydrate,hydrosilyl)on the catalytic transfer hydrogenation of levulinic acid to ?-valerolactone,and optimized the reaction conditions.The results showed that the conversion of levulinic acid was 95.1%and the yield of ?-valerolactone was 94.1%when the reaction temperature was 180? and the reaction time was 4 h under the 1 wt%Co0.5-Re0.5/TiO2 catalyst,the molar ratio of levulinic acid,formic acid and triethylamine was 1:4:4,the amount of the catalyst was 0.1 g.Then,Ni-Re bimetallic catalyst was prepared for the hydrodeoxygenation of oleic acid to prepare long-chain alkanes.The results showed that using 1 wt%Ni0.8-Re0.2/NMC catalyst,isopropanol as solvent and hydrogen donor,reacting at 330? for 2 h,oleic acid can be completely converted.The yield of heptadecane was 84.7%,and the yield of octadecane was 9.9%.According to XPS analysis,Ni was present in elemental form,and Re is present in the form of ReO2.Butyric acid,a model of oleic acid,was more likely to adsorb on the ReO2 crystal plane by calculation of the adsorption energy,which is-1.121 eV.So that the conversion rate of the catalyst Re/NMC to oleic acid was higher than that of Ni/NMC.By calculation of the dissociation process of isopropanol,on the Ni crystal plane,isopropanol tended to leave the hydrogen atom of the aC firstly,and then the hydrogen atom on the hydroxyl group was removed.The dissociation process on the ReO2 crystal plane was removing the hydrogen atom on the hydroxyl group firstly,and then removing the hydrogen atom on the aC.By simulating the deoxidation process of butyric acid on the Ni crystal plane,it was found that butyric acid was more inclined to remove oxygen atoms through the decarbonylation pathway.The reaction sequence was C3H7COOH?C3H7COO�?C3H7CO�?C3H7�.The rate control step is removing an oxygen atom from the butyrate.The excellent catalytic performance of Ni-Re bimetallic catalysts was attributed to higher oleic acid adsorption capacity and appropriate hydrogen ion concentration;The higher selectivity to heptadecane was attributed to the lower activation energy of the decarbonylation pathway.