Theoretical Design And Experiments Of Dibenzofuran Hydrodeoxygenation Over Pt And Ni-based Catalysts

The low-temperature coal tar and coal liquefaction oil,as the coal-based crude oil,contain much more oxygen-containing compounds that result in consuming excess hydrogen,having poor thermal stability,and low heating value when downstream processing.Catalytic hydrodeoxygenation is one of efficient methods to upgrade coal-based crude oil.However,only limited researches are performed on the mechanism of hydrodeoxygenation and,therefore,innovation of more efficient and stable catalysts is less progressed and still remains a challenging subject.In this study,density functional theory calculations are employed to elaborate a deep insight and analysis in the hydrodeoxygenation of dibenzofuran,which is chosen as a model compound of coal-based crude oil,on the Pt（111）and Ni（111）surface.Then according to the calculated results,the Ni-TiO_x/SBA-15 catalyst was designed and prepared.The small amount addition of TiO₂ has greatly improved the hydrodeoxygenation performance of Ni/SBA-15 catalysts.The main results and conclusions are as follows:（1）There is a competitive relationship between the ring opening and hydrogenation of tetrahydrodibenzofuran,as well as hexahydrodibenzofuran.Increasing the temperature and decreasing the hydrogen pressure can promote their ring-opening,and reduce the yield of dodecahydrodibenzofuran.The adsorption of dodecahydrodibenzofuran and cyclohexylcyclohexanol are weak on mental surface,their ring-opening and deoxygenation are difficult due to the high barriers.（2）On the Pt（111）surface,cyclohexylphenol is prone to go through the nonconsecutive hydrogenation.The deoxygenation barriers and reaction energies are reduced with increasing degree of hydrogenation of cyclohexylphenol.The pentahydrocyclohexylphenol has the lowest deoxygenation barrier and possibly deoxygenated to bicyclohexane.On the Ni（111）surface,cyclohexylphenoxy is generated.One part of cyclohexylphenoxy is directly consecutive hydrogenated to cyclohexylcyclohexanone,and then hydrogenated on O atom to form pentahydrocyclohexylphenol.Another part is hydrogenated to cyclohexylphenol,following consecutive hydrogenated to cyclohexylcyclohexanol.The hydrogenated intermediates of 2-cyclohexylphenol have higher deoxygenation barriers than cyclohexylphenol and cyclohexylcyclohexanol.Therefore,cyclohexylcyclohexanol is one of the main products of dibenzofuran hydrodeoxygenation on the Ni（111）surface.（3）Because of the low adsorption energies of dodecahydrodibenzofuran and cyclohexylcyclohexanol on the metal surface,Ni-TiO_x/SBA-15 catalyst was designed and prepared.At the interfacial site of Ni-TiO_x/SBA-15 catalyst,Ni and unsaturated Ti can synergistically adsorb dodecahydrodibenzofuran,cyclohexylcyclohexanol and other oxygen-containing intermediates.That can enhance their adsorption,activate their C-O bonds,and reduce their ring opening and deoxygenation barriers.In addition,TiO₂ cluster can inhibit the cyclohexylphenoxy hydrogenation to cyclohexylphenol,thereby promoting the formation of pentahydrocyclohexylphenol and increasing the deoxygenation rate.With the molar ratio of Ti improving,the deoxidizing ability of the catalyst gradually increases.The highest yield of bicyclohexane is confirmed as the molar ratio of Ni/Ti about 1:3.