Performances Of TiO₂, CeO₂-Promoted Ni₂P Catalysts In Hydrogenation Reactions

The reformate process which was used to produce chemical grade BTX (Benzene, Toluene and Xylene) aromatics in the refineries was faced with the problem that a small amount olefins can be removed while the aromatics was not saturated. With the large-scale continuous reforming units were running and the need of deep reactions, this problem became more and more prominentWe prepared a series of TiO₂-promoted bulk Ni2P and CeO₂-promoted bulk Ni₂P catalysts(Ti_x-Ni₂P, Ce_x-Ni₂P, Ti_x-Ni₂P(â… ), Ce_x-Ni₂P(â… ), where x represents the Ti/Ni, Ce/Ni molar ratio) with co-precipitation and impregnation methods. And using 1.5 wt% 1-heptene in toluene and 1% phenyl acetylene in alcohol as reactants to evaluate their hydrogenation activities.XRD and XPS characterization of TiO₂-promoted bulk Ni₂P catalysts, indicated that TiO₂ species were mainly located on the surface of the catalysts, and did not react with Ni₂P to form NiP₅Ti₂ or a solid solution, but facilitated the formation of Ni₂P and had strong electronic interaction with surface species of the catalysts, leading the surface to an "electronic-rich" state. The hydrogenation activity of Ni₂P was significantly enhanced by the addition of TiO₂, and the hydrogenation activity of Ti_x-Ni₂P increased with increasing TiO₂ content under the Ti/Ni molar ratios studied in present work. Under the Ti/Ni molar ratio 0.01, the catalyst showed promising performance in selective hydrogenation of 1-heptene, leaving toluene almost unaffected. However, at Ti/Ni molar ratio higher than 0.01, both 1-heptene and toluene were hydrogenated.The promoter effects of CeO₂ were similar to TiO₂.The formation of Ni₅P₄ or Ni₂P₄O₁₂ was depressed and the particle size of Ni₂P was reduced by the introduction of CeO₂. Formations of Ce³⁺species were in the process of high-temperature reduction, the electrons transferred to the surface of Ni₂P, increasing the electron cloud density and thus contributing to a high hydrogenation reactions of nickel phosphides. Introduction of a small amount of CeO₂ can significantly improve the hydrogenation activity of N_i2P catalyst. The catalysts which were prepared with co-precipitation method and the Ce/Ni molar ratio was 0.01, 0.03, and 0.05 showed good performances of selective hydrogenation of olefins, while the aromatics were no loss. When the Ce/Ni mole ratio was larger than 0.01, 1-heptene and toluene both were reacted in hydrogenation. The TiO₂ or CeO₂ promoted bulk Ni₂P catalysts which were prepared by impregnation method and the Ti / Ni mole ratio and Ce / Ni mole ratio were 0.1, can catalyze the triple bond and double bond of aramatics in hydrogenation reactions, showed strong hydrogenation activity.