Preparation Of Ni₂P/Ce-Al₂O₃ Catalyst And Its Saturated Hydrogenation Performance Of Naphthalene

The aromatic hydrocarbon components in the direct coal liquefaction oil could be transformed into the jet fuel which riches in the cycloalkanes by the saturated hydrogenation of aromatic technology.Considering the components of direct coal liquefaction oil?containing aromatic hydrocarbon?and the component requirement of jet fuel?cycloalkanes?,the key point for the saturated hydrogenation technology is to develop an efficient catalyst with high saturated activity.Traditional transition metal sulfide catalyst is insufficient for aromatic saturation due to its poor hydrogenation activity.Though the noble metal catalyst possesses outstanding aromatic saturation activity,it is expensive,scarce and unable to have a wide range of industrial application.In recent years,a novel Ni₂P catalyst has been widely used in the process of hydrodesulfurization?HDS?and hydrodenitrogenation?HDN?and shows promising hydrogenation activity and stability due to its special crystal structure and electronic property of Ni₂P.As the representative model compound of coal liquefied jet fuel distillate,naphthalene usually be selected to investigate the saturated hydrogenation performance of the catalyst.In this paper,we choose naphthalene as a model compound and take decalin as the target product,the influence of Ce-Al₂O₃ support,the Ni/P molar ratio and the Ni₂P loading on the crystal structure,the number of surface active sites,the dispersity of Ni₂P/Ce-Al₂O₃ catalyst were investigated.The catalytic activity of catalysts for naphthalene saturated hydrogenation was evaluated in a three-stage fixed bed reactor.The main results and conclusions obtained in this paper were as follows:?1?The Ce-Al₂O₃ were synthesized by sol-gel method.the addition of Ce to Al₂O₃ could regulate the coordination number of Al,weaken the interaction between the P and Al₂O₃,and ensure the formation of Ni₂P.Comparing with the unsupported Ni₂P catalyst,the Ni₂P/Ce-Al₂O₃ catalyst possessed larger surface area and more surface active sites.?2?According to the forming mechanism of Ni₂P in the preparation of supported nickel phosphide catalyst by means of temperature-programmed reduction?TPR?,a series of Ni₂P/Ce-Al₂O₃ catalysts with different initial Ni/P molar ratio were prepared.The result shows that:the optimal Ni/P molar ratio is1.25,and pure phase of Ni₂P could not obtained when the Ni/P molar ratio is greater than 1.25 due to the lack of phosphide.Comparing with the catalyst with the Ni/P molar ratio of 1.25,the catalyst with Ni/P molar ratio less than 1.25 also could form pure phase of Ni₂P.However,the catalyst possessed poor saturated hydrogenation activity and dispersity of catalyst duo to the excess of phosphide.A series of Ni₂P/Ce-Al₂O₃ catalysts with different Ni₂P loading?5 wt%,11 wt%,17 wt%,23 wt%?were prepared to obtain the correlations between the catalytic saturated hydrogenation activity and the number of surface active sites of catalyst.The number of surface active sites of catalyst was quantified by means of CO chemisorption at room temperature.The catalytic activity of saturated hydrogenation of naphthalene over Ni₂P/Ce-Al₂O₃ catalysts were carried out at613 K and 3.4 MPa,the H₂/oil molar ratio of 600.The result indicated that the number of surface active sites of Ni₂P/Ce-Al₂O₃ catalyst increase at first then decrease with the loading of Ni₂P increased.Catalytic evaluation showed that the Ni₂P/Ce-Al₂O₃ catalyst with 17 wt%Ni₂P loading obtained the the best hydrogenation activity.The conversion of naphthalene is 95%,and the selectivity to decalin is 76%,which was ascribed to the highest CO chemisorption amount?26.6?mol/g?and corresponding increased active sites.