침전법으로 제조한 Ni / SiO2 촉매에서 규산니켈의 생성에 따른 촉매의 특성변화 = Effect of Nickel - silicate Formation on Catalytic Properties of Ni / SiO2 Prepared by Precipitation Method

다국어 초록 (Multilingual Abstract)

Ni/kieselguhr catalysts have been prepared by precipitation of nickel nitrate with either ammonium hydroxide or sodium carbonate in a solution where kieselguhr particles are suspended. Changes in the catalyst properties with the preparation conditions have been studied primarily by observing the X-ray diffraction patterns of the sample catalysts. The amount of nickel silicate formed on the catalyst surface during the precipitation step is closely related to the properties of the catalysts. That is, formation of nickel silicate on the catalyst increases the total surface area of the catalysts, and reduces the nickel particle size as well as its reducibility. Nickel silicate also makes the silica surface rough, thus reducing the pore opening of the support. Nickel silicate is enhanced on the catalyst when the alkaline precipitant, preferably sodium carbonate than ammonium hydroxide, is injected slowly into the nickel nitrate solution which is maintained at high temperature. Aging of the precipitation solution at high pH after fast precipitation enhances the formation of nickel silicate on the catalyst, particularly when sodium carbonate is used as a precipitant. However, when ammonium hydroxide is used as a precipitant,slow precipitation without aging is more effective for the nickel silicate formation than fast precipitation followed by aging. The hydrogenation rates of unsaturated fatty acid on the nickel catalysts decrease significantly when nickel silicate is formed on the catalyst to certain extents. This seems to result from retarded diffusion of the large reactant molecules into the catalyst pores, whose opening size has been reduced by the nickel silicate formation.