Hydrodeoxygenation Of Dibenzofuran Over Ni/Ordered Mesoporous SiO₂-Al₂O₃ Catalysts

Lignite coal tar produced at low temperature is an important product of pyrolysis.High-quality fuels can be obtained by catalytic hydrogenation because it contains a large amount of aliphatic and aromatic hydrocarbons,thereby making it a potential energy supplement for petroleum.However,large amounts of oxygenated compounds can cause problems such as low heating value and poor stability.Catalytic hydrodeoxygenation（HDO）can effectively remove oxygen heteroatoms and improve the oil quality.Ni-based catalysts have a wide range of applications in the catalytic hydrodeoxygenation due to its high hydrogenation activity.Dibenzofuran（DBF）,a typical oxygen-containing compound in coal tar,is selected as a HDO model compound.The performance of Ni-based catalysts on different supports including ordered mesoporous alumina（OMA）,SBA-15 andγ-Al₂O₃ were tested in a batch reactor.By comparing the HDO performance and product distribution,the effects of the active metal Ni,support pore structure and Lewis acid on the HDO of DBF were studied.Secondly,the effects of Br?nsted acid sites on HDO by silica doping in the synthesis of ordered mesoporoes alumina（OMA）were explored,and the purpose of preparing ordered mesoporous SiO₂-Al₂O₃ supports for enhancing the HDO performance of DBF is achieved.The main results and conclusion obtained from this thesis are as follows:（1）According to the HDO performance of DBF and the product distribution on the three prepared catalysts,the results show that DBF only undergoes hydrogenation（HYD）pathway and no direct deoxygenation（DDO）pathway occurs because of the high hydrogenation activity of Ni metal.Ni can hydrogenate the benzene ring and break the C-O bond,while Lewis acid sites can cooperate with Ni sites to activate oxygen-containing intermediate products and promote C-O bond cleavage.In addition,the well-ordered pore structure can reduce the mass transfer resistance and improve the HDO performance of the catalyst.（2）According to the HDO performance of DBF and the product distribution on a series of Ni/SiO₂-Al₂O₃ with different silica doping,the results show that Br?nsted acid sites on the surface of the support can cooperate with Ni to break the sp³ C-O bond and promote the alcohol hydroxyl dehydration reaction.（3）The silica doping can not only adjust the support acidity,but also cause the change of the pore structure and the specific surface area of the as-prepared supports.When the silica doping is excessive,the amorphous silica can block the pores of the support and reduce the dispersion of the Ni,and further jeopardise the catalytic performance.（4）When the silica doping is 20wt%,the Ni/20Si-Al₂O₃ catalyst show the best HDO performance of DBF:the DBF conversion is 98.2%,and the hydrodeoxygenation degree is 95%,and the yield of target products BCHs is 84.5%.