Study On Dechlorination Method Of Suppported Ru/ac Catalyst For Ammonia Synthesis Prepared By Rucl₃ Precursor

The promoted Ruthenium-based catalysts are created a sensation as second-generation catalysts for ammonia synthesis. RuCl₃ is considered as an ideal active precursor for its stabilization and cheapness. However, chloride ion is poison to catalyst activity. So it is very important to study how chloride ion was removed from catalyst. In this thesis, dechlorination method was studied in detail, and the catalyst activity in low temperature has increased from about 17% to higher than 20%. Besides, chlorine poisonous mechanism was primarily discussed. The main results are as follows:1. The effect of hydrogen reduction on dechlorination was studied. Reduction temperature, time and reduction gas space velocity all have effects on catalyst activity. More chloride ion was removed in higher temperature, but it is disbennifit to catalyst activity for support methanation and ruthenium particle sintering in high temperature. During the previous 12 hours, chloride ion was removed little by little as reduction time was prolonged, the catalyst activity increased gradually too. Then continually prolonged the reduction time, neither the amount of removed chloride ion or catalyst activity was increased. High property catalyst was achieved when reduced in 200℃, 1080h^-1' for 12 hours.2. It is found that deposition condition had influences on catalyst activity. The effect of kind of precipitator, precipitator concentration, deposition time and deposition temperature on catalyst activity was studied. The influence of precipitator on catalyst activity arranges as follows: NH₃H₂O> KOH> NaHCO₃>carbamide>Na₂CO₃>diluted water; In room temperature, deposited by 3% of ammonia solution is the best, other precipitator concentration have no effect on catalyst activity; It seems that 65℃is the modest deposition temperature when deposited by KOH. Na₂CO₃,NaHCO₃,carbamide or hot diluted water; 7 hours is enough for deposition.3. Effect of washing process on dechlorination and catalyst activity was studied. (1) Washed in continuous diluted water: the low the water velocity the more the chloride ion was removed and the high the catalyst activity was reached, but it needs more time and water for washing. (2) Washed intermittently when washing temperature is from 30℃to 90℃: washed in 80℃for 3 times(90ml/time) is optimal.4. The influence of hydrazine hydrate reduction on dechlorination was primarily investigated. Chloride ion can be efficiently removed when reduced by hydrazine hydrate, and the activity of the catalyst paralleled to that of H₂ reduced catalyst sample. But the poisonous feature is its main disadvantage for using.5. The chlorine poisonous mechanism was simply discussed. Chloride ion has great effect on catalyst activity at low temperature.