Low Temperature Synthesis Of Ni₂P/Al₂O₃ Catalyst And Its Hydrogenation Saturation Performance Of Naphthalene

Coal tar is rich in polycyclic aromatic hydrocarbons.At present,catalytic hydrogenation of coal tar is mainly used to produce qualified gasoline and diesel products through hydrocracking reaction,but its reaction condition is usually harsh and consumes a large amount of hydrogen.If the two rings and three rings aromatics rich in coal tar were converted into hydroaromatics and cycloalkanes by hydrogenation saturation reaction,the resultant products would be an ideal component of high performance jet fuel.However,due to the obvious difference between coal tar and petroleum raw materials,traditional petrochemical hydrogenation catalysts are difficult to meet the demand of coal tar to produce jet fuel.Therefore,how to obtain high hydrogenation saturation active catalyst is the key point to achieve the low-temperature coal tar to high-performance jet fuel.The traditional transition metal sulfide catalyst has poor aromatic hydrogenation saturation activity.Although the noble metal catalyst has high aromatic hydrogenation saturation activity,it is expensive and easily poisoned,which limits its wide application.In recent years,Ni₂P catalyst has shown high intrinsic hydrogenation activity in hydrodesulfurization?HDS?and hydrodenitrogenation?HDN?reactions due to their special crystal morphology and physicochemical properties,and are expected to become a new generation of highly efficient aromatic hydrogenation saturation catalyst.The hydrogenation activity of the Ni₂P catalyst was closely related to the particle size of Ni₂P and the small particle size Ni₂P had higher hydrogenation activity.The Ni₂P catalyst was generally prepared by a conventional temperature programmed reduction method?TPR?.However,the P-O bond in the precursor selected by the method was stable and it can be broken when the temperature is higher than 600°C.The high temperature not only increased the energy consumption of the preparation process,but also promoted the aggregation of Ni₂P to form large particles,which reduced the dispersion of the catalyst.The Al₂O₃ support has a low cost,good mechanical properties,a suitable specific surface area and pore structure,and has become a carrier for a hydrogenation catalyst commonly used in the industry.However,at high temperature,there was a strong interaction between the P species in the precursor and the Al₂O₃ support commonly,which inhibited the formation of the Ni₂P phase and limited the application of the Al₂O₃ support in the Ni₂P catalyst.It is generally believed that the interaction between the P species and the Al₂O₃ support was weak at low temperature,and the inhibition of Ni₂P production was alleviated.Therefore,in this work,combined with the advantages of thermal decomposition of hypophosphite method for the preparation of Ni₂P active phase at low temperature and the excellent properties of Al₂O₃ carrier,Ni₂P/Al₂O₃ catalyst was prepared by thermal decomposition of hypophosphite method.The influence of Ni₂P loading and reduction temperature on the crystal phase structure,the number of surface active sites and surface properties of Ni₂P/Al₂O₃ catalyst was investigated.We choose naphthalene as a model compound for hydrogenation of aromatic components in coal tar and take decalin as the target product,investigating the hydrogenation saturation performance of the catalyst.The research contents and conclusions of the thesis mainly include:?1?Ni₂P/Al₂O₃ catalyst was successfully prepared by using Al₂O₃ as carrier,nickel acetate as nickel source and ammonium hypophosphite as phosphorus source in hydrogen atmosphere at 400°C.The preparation conditions were milder than the temperature-programmed reduction method,and the process was relatively simple.?2?The effects of different Ni₂P loadings?5wt%,10wt%,15wt%,20wt%?on the structure of Ni₂P/Al₂O₃ catalysts and the hydrogenation saturation performance of naphthalene were investigated.The results show that with the increase of loading,the specific surface area of the catalyst gradually decreased,the particle size of Ni₂P increased gradually,and the P-OH deposited on the surface of the catalyst increased and the number of surface active sites in the catalyst increased first and then decreased.When the Ni₂P loading was 10wt%,the catalyst has the highest CO adsorption capacity(30?mol·g^-1)and exhibits optimal naphthalene hydrogenation activity,the conversion of naphthalene was98%,and the selectivity of decalin was 98%.?3?Based on the determined optimal Ni₂P loading of 10wt%,the effects of different reduction temperatures on the active phase formation and naphthalene hydrogenation saturation performance were investigated.The results show that the Ni₂P active phase can be prepared by reducing catalyst precursor among 300-500°C.As the reduction temperature increases,the particle size of Ni₂P gradually increased,and the phosphate content deposited on the surface of the catalyst gradually decreased.When the reduction temperature was 400°C,Ni₂P/Al₂O₃catalyst had the highest hydrogenation saturation activity,the conversion of naphthalene was 98%,and the selectivity of decalin was 98%.The high hydrogenation saturation activity is attributed to the synergy between the small particles of Ni₂P and the suitable acidity.