| Polycyclic aromatic hydrocarbons?PAHs?are usually found in petroleum and aromatic oil-filled rubber and paint products.Their strong volatility can cause carcinogenic effects on humans and animals and PAHs can cause carbon deposits in gasoline.Since the EU issued REACH?Registration Evaluation Authorization and Restriction of Chemicals?regulations,aromatic oils in the rubber industry have been gradually replaced by naphthenic oils.At present,in the process of crude oil refining and production of rubber-filled oil,the efficient and directed catalytic hydrogenation of condensed aromatic hydrocarbons is a very meaningful work.Naphthalene,as a typical condensed polycyclic aromatic hydrocarbon,is usually used as a model compound in scientific research to study the activity of the catalyst in the catalytic hydrogenation process.The selectivity of decalin in the product reflects the deep hydrogenation ability of the hydrogenation catalyst.In this thesis,hydrogenation of naphthalene is used as a model reaction to study the hydrogenation performance of molybdenum carbide catalysts.Samples such as?-Mo2C,?-Mo C1-x,molybdenum carbide-supported metal samples,and alumina-supported molybdenum carbide are prepared by temperature programmed carbonization.The physicochemical properties of the catalyst were characterized by XRD,BET,XPS,SEM,TEM,ICP,HR-TEM and other characterization methods.At the same time,the catalytic activity,stability and reaction condition of the molybdenum carbide-based catalysts in the hydrogenation of naphthalene were investigated.Main research contents and experimental results are as follows:?1?Preparation of?-Mo2C and?-Mo C1-x,and test of the the catalyst activity in the fixed bed under the same activation and reaction conditions.The research results show that?-Mo2C does not show catalytic activity in naphthalene hydrogenation below 200°C,which is consistent with the results obtained by previous researchers.The?-Mo C1-x has a conversion rate of about 30%at 50°C,100%conversion of naphthalene at 150°C,and 28%selectivity to decalin.Combined with the results of XRD,XPS,BET,etc.,it is found that compared with?-Mo2C,?-Mo C1-x has a higher specific surface area and a higher Mo3+corresponding proportion of molybdenum carbide,so its catalytic activity is higher.In addition,from the stability results of naphthalene hydrogenation,?-Mo C1-x has poor stability in naphthalene hydrogenation.Through XRD and XPS analysis,the particles of the sample become smaller after the reaction and have a certain degree of lattice expansion.The surface Mo3+corresponding proportion of molybdenum carbide has decreased to some extent.It shows that the bulk phase of the catalyst changes before and after the reaction,and the Mo3+corresponding to the surface of the molybdenum carbide is converted or covered by carbon deposition.?2?Samples of molybdenum carbide loaded with different metals were prepared by the temperature-programmed carbonization of their precursors in CH4/H2 atmosphere.XRD and BET characterization results show that 0.5%Pd/Mo C,0.5%Pt/Mo C,0.5%Ru/Mo C catalysts are?-phase(?-Mo C1-x)with specific surface area greater than 140 m2/g,while 0.5%Ni/Mo C and 0.5%Co/Mo C is?-phase??-Mo2C?,and its specific surface area is small?about 30 m2/g?.In the fixed bed activity test of naphthalene hydrogenation,Pd,Pt,and Ru-supported molybdenum carbide are significantly better than Ni and Co-supported molybdenum carbide,of which Pd-supported molybdenum carbide?0.5%Pd/Mo C?shows the optimal activity.The conversion rate of naphthalene at 50°C reaches 95%.When the reaction temperature rises to200°C,it is converted to 100%and the selectivity to decalin is greater than 80%.The surface element analysis results in the original XPS data indicate that the Mo3+supported by noble metals such as Pd,Pt,Ru and Mo are supported by transition metals such as Co and Ni,the ratio of Mo3+on the surface of the former is greater than that of the latter,of which 0.5%Pd/Mo C has the highest proportion of Mo3+corresponding to molybdenum carbide.Through the study of 0.5%Pd/Mo C process conditions,it is found that temperature increase,pressure increase and space velocity decrease can effectively improve the catalytic activity.After the stability test of 0.5%Pd/Mo C at 150?,it is found that the addition of Pd will definitely improve the stability of the catalyst(compared with?-Mo C1-x).The XRD and XPS results of the catalyst before and after the reaction show that the bulk crystal form of the catalyst changes little after the reaction The proportion of molybdenum carbide corresponding to Mo3+on the surface has decreased to a certain extent,indicating that the molybdenum carbide corresponding to Mo3+on the surface has been converted or masked by carbon deposition.?3?The?-Al2O3 supported molybdenum carbide catalyst is prepared by excessive impregnation and carbonization,and the naphthalene hydrogenation activity test is carried out in a slurry bed.Among them,the 20%Mo2C/?-Al2O3 catalyst showed excellent activity.When the reaction time is 12 h,the conversion rate is more than 99%and the selectivity of decalin is 3%.XRD characterization results show that the molybdenum carbide with different loadings on the?-Al2O3 is?phase,and as the loading increases,the dispersion of molybdenum carbide on the surface decreases and the degree of crystallization increases.In addition,0.5%M-20%Mo2C/?-Al2O3?M is metal?samples obtained by excessive impregnation of different metals?Pt,Ru,Co,Ni?and ammonium molybdate were also studied.The naphthalene hydrogenation activity test results show that the addition of the second metal M can increase the catalytic activity of 20%Mo2C/?-Al2O3,and the activity of 0.5%Pt-20%Mo2C/?-Al2O3 is better,after12 hours of reaction the hydrogenation conversion of naphthalene is close to 100%,and the selectivity to decahydronaphthalene is about 70%.After studying Pt-20%Mo2C/?-Al2O3 with different Pt loadings,it is found that the higher the Pt loading,the higher the conversion and selectivity of the catalyst.TEM characterization results show that the crystal form of molybdenum carbide on 0.5%Pt-20%Mo C/?-Al2O3 is part of?-phase and part of?-phase. |
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