Study On Preparation Of Mesoporous Ni/CeO₂ Catalyst For Water Gas Shift Reaction

It is well known that mesoporous materials have special properties in electricity,chemistry and catalysis. Metals supported on meso-porous oxides are likely in high dispersion state due to their high specific surface areas. Water gas shift reaction (WGSR) is one of the important steps in hydrogen production from hydrocarbons for fuel cells. Ni-CeO₂ shows high activity for high tempreture WGSR, however the selectivity remains to be improved. In our work, meso-porous ceria supported nickel catalysts have been prepared and used for high temperature WGSR, in order to improve their catalytic activities as well as the selectivities.The Ni/meso-CeO₂ was prepared with four method, that was, wet impregnation of mesoporous CeO₂ supported by nickle nitrate solution and nickle ammonia complex solution respectively, one-step synthesis of mesoporous Ni/CeO₂ by template method with cation surfactant CTAB and Non-ionic surfactant P123 as template respectively. The preparation conditions were investigated and the catalytic performance for high temperature WGSR over such catalysts were also tested. The main results are as follows:1. The catalyst prepared by one-step synthesis with P123 as template had high specific surface area and narrow pore size distribution, and nickel supported on this meso ceria was highly dispersed. The surface area and average pore size of this prepared Ni/meso-ceria were 214 m2/g and 2.44 nm respectively. This catalyst showed greater activity than others for water gas shift reaction and the conversion of CO was close to 81% and the yield of CH4 approached 9% at 400 oC in reformate under 60000 cm3·gcat-1·h-1.2. The catalysts prepared by one-step synthesis with P123 under different pH values indicated that high pH value was prone to produce high surface area catalysts and in favor of good activity.3. The catalysts prepared by one-step synthesis with P123 under different aging times indicated that the catalyst which was not aged tends to show high activity and good selectivity.4. The catalysts prepared by one-step synthesis with P123 under different calcination temperatures showed that surface areas of the catalysts decreased from 214 m2/g to 165 m²/g with increase of calcination temperature from 450℃to 550℃.And the conversions of CO decreased from 81% to the value under the equilibrium conversion.5. We have evaluated the activity and selectivity of the catalyst prepared by one-step synthesis with P123 under different space velocities.The results showed that the CO conversion and the yield of CH₄ decreased with the increase of space velocities from 60000 to 160000 cm³Â·gcat^-1·h^-1.Under the high space velocities of 160000 cm3·gcat^-1·h^-1, CO conversion was about 75% and the yield of CH4 was 4%.