Hydrodeoxygenation Of Dibenzofuran Over Bimetallic Ni-Fe Catalysts

The medium-low temperature coal tar can be used as transportation fuel after processing.However,it contains a certain amount of oxygen-containing aromatic compounds.The catalytic hydrodeoxygenation will directly affect the fuel quality.These oxygenated aromatic compounds are mainly phenolic and furan compounds according to functional groups.Dibenzofuran has a large molecular size and a very low reactivity.It is considered as a model compound for hydrodeoxygenation of furan in coal tar.Conventional single metal Ni catalyst had strong hydrogenation ability,but had weak ability to break the C-O bond.In order to improve the hydrodeoxygenation performance of Ni catalyst,bimetallic Ni-Fe catalyst was prepared by combining strong oxophilic Fe.The hydrodeoxygenation performance was studied in an autoclave at 280 ? and 6.5 MPa.The mechanism of oxophilic Fe in the hydrodeoxygenation of dibenzofuran was also elucidated.Firstly,SBA-15 was chosen as the support because of its ordered mesoporous structure,which was beneficial to the mass transfer of macromolecular dibenzofuran.Ni/SBA-15,Fe/SBA-15 and Ni-Fe/SBA-15 catalysts of different Fe loadings were prepared by the incipient wetness impregnation method.The effect of Fe loading on the catalytic performance of Ni/SBA-15 was investigated by comparing the hydrodeoxygenation performance of different catalysts.Among them,5Ni-2Fe/SBA-15 had the most excellent hydrodeoxygenation performance.Secondly,Al was introduced into the SBA-15 framework to prepare the 5Ni/Al-SBA-15 catalyst.Its acidity was equivalent to that of 5Ni-2Fe/SBA-15 catalyst.By comparing the product distribution of the oxygen-containing intermediate 2-cyclohexylcyclohexanol on them,it was confirmed that the oxophilicity of Fe played a major role.Finally,Ni-Fe/Al-SBA-15 catalysts were prepared and the effect of support acidity on the hydrodeoxygenation of dibenzofuran was investigated.The main results and conclusions are as follows:(1)At 280 ?,6.5 MPa,the reaction pathway of dibenzofuran on bimetallic Ni-Fe catalyst was hydrogenation-dehydration route(HYD),not direct deoxygenation route(DDO).Because DDO required higher activation energy than HYD,usually occurred under high temperature and low pressure conditions.(2)The addition of proper amount of Fe promoted the fracture of C-O bond and improved the hydrodeoxygenation activity of Ni/SBA-15.Among them,the 5Ni-2Fe/SBA-15 catalyst showed the most excellent performance,with superior yield of 82.8% for bicyclohexane and 99.9% conversion of dibenzofuran.The addition of excess Fe covered a portion of the Ni active site,which reduced the hydrodeoxygenation activity of the catalyst.(3)By comparing the product distribution of 2-cyclohexylcyclohexanol on 5Ni-2Fe/SBA-15 and 5Ni/Al-SBA-15 catalysts,it was confirmed that the oxophilicity of Fe played a major role in the hydrodeoxygenation of dibenzofuran,rather than acidity.(4)When Fe was added to the 5Ni/Al-SBA-15 catalyst,the reaction rate was significantly accelerated.It was attributed to the synergy between the acidity of support and the oxophilicity of Fe.The space-time conversion of DBF and the space-time yield of BCHs were significantly improved.In the hydrodeoxygenation of dibenzofuran on bimetallic Ni-Fe catalyst,the oxygencontaining intermediate 2-cyclohexylcyclohexanol undergone hydrogenolysis under the action of oxophilic Fe,directly breaking the C-O bond to form the target product BCHs.