Study On Supercritical Fluid Preparation Of Supported Ni Catalyst

In this paper, we prepared a supported Ni/Al₂O₃catalyst by supercritical CO₂impregnation technique, using supercritical CO₂as impregnation medium, active aluminumoxide as catalyst carrier and Ni （NO₃）2as active precursor, and studied the hydrogenationperformance of the supported Ni-based catalyst based on glucose hydrogenation reactionmodel. We studied the effects of the temperature and pressure of CO₂fluid, the reaction time,the mass ratio of the active precursor and carrier, kinds of the cosolvent, the cosolvent amountand the reduction temperature on the Ni loading amount as well as the activity of the catalyst.The results showed that the supercritical CO₂impregnation method could effectively improvethe Ni loading amount in comparison with the conventional water impregnation method so asto improve the catalytic activity of the supported Ni/Al₂O₃catalyst. In the experiment range,the catalyst had the optimum Ni loading amount under the conditions of supercritical CO₂temperature60℃, pressure8MPa, reaction time3h, methanol cosolvent0.5ml, and at areduction temperature of600℃, the catalyst had the best activity, which was1.65times of thecatalyst prepared by the water impregnation method. The Ni/Al₂O₃catalyst samples werecharacterized by XRD、SEM、BET、XPS、TG、DTA. The results showed that the supportedNi/Al₂O₃catalyst, prepared by supercritical CO₂impregnation technique, had a larger Niloading amount, the active component Ni had a well distributed on the carrier aluminumoxide, between Ni and the catalyst carrier had a strong interaction force, so the Ni/Al₂O₃catalyst had a better hydrogenation performance.Make a preliminary exploration on the doped Ni-B/Al₂O₃catalyst. The results showedthat, for the glucose hydrogenation reaction, the introduction of B to the Ni/Al₂O₃catalyst inthe form of boric acid is bad to the catalytic activity. Taking potassium borohydride as thereducing agent to prepared Ni-B/Al₂O₃catalyst is good to the catalytic activity, which was1.76times of the Ni/Al₂O₃catalyst. The Ni-B/Al₂O₃catalyst has a smaller average particlessize of Ni, the active component Ni had a well distributed on the carrier aluminum oxide, theinteraction between the carrier and the active center is enhanced.Make a preliminary exploration on the rare earth element doping Ni/Al₂O₃catalyst. InLa、Nd、Ce、Sm four kinds of rare earth elements, doped La catalyst samples had the bestcatalytic activity. In the experiment range, at higher loadings of Ni （9.20%）cases, doped3%La, the catalyst had the best activity, which was1.36times of the undoped Ni/Al₂O₃catalyst. The Ni-La/Al₂O₃catalyst has a smaller average particles size of Ni, the active component Nihad a well distributed on the carrier aluminum oxide, the interaction between the carrier andthe active center is enhanced. At the same time, the addition of La can prevent Ni graingrowth and sintering, so it can improve the catalytic activity of the Ni/Al₂O₃catalyst.