Structure Control And Its Performance Of The Ru/Ac Catalysts For Ammonia Synthesis

The ruthenium-based catalysts have been considered as the second-generation catalysts for ammonia synthesis,for the characteristics of high activity at low temperatures and low pressure.In order to further enhance the performance-price ratio and to strengthen the stability of catalysts,the catalysts of Ru/AC for ammonia synthesis were prepared,with alkali metals and alkaline earth metals as additives.The support and catalysts were characterized by N2 physical adsorption,H2-TPR,H2-TPD,N2-TPD,MS,GC,TEM respectively.The activity of catalysts and the methanation of support were measured at a certain temperature and pressure.The effect of ammonia treatment for the activated carbon support and the Ru/AC catalysts were discussed,and the influence of Sr additives on the activity and the stability of Ru/AC catalysts was studied for ammonia synthesis.The effect of the second high-temperature heat treatment of activated carbon(under Argon atmosphere,800?1600 ?,referred to as secondary heat treatment)was also studied behind graphitization treatment at high temperatures and reaming oxidation treatment.The main significant results were as follows:The specific surface area and pore structure of activated carbon could be optimized under ammonia treatment.The optimum treatment temperature was 1100 ?,and the suitable treatment time was 2 h.When HNO3 and K2CO3 were used as the active agents under ammonia atmosphere,the specific surface area and the pore structure of activated carbon could be greatly improved,and the specific surface area could be 1850 m2/g and 1530 m2/g respectively.The catalysts of Ru/AC for ammonia synthesis were prepared with the activated carbon as supports treated with ammonia under different temperatures.The treated temperature of activated carbon has a great impact on the performance of catalyst.The stability of the catalysts at the treated temperature of 700 ?-900 ? was better.For the Ba-Ru/AC and Ba-K-Ru/AC catalysts of ammonia synthesis,the addition of Sr enhanced the anti-methane ability of the catalysts,moreover the activity and stability of catalysts could be better.This was mainly because the distribution of Ba additive and Ru particles were more uniform due to the addition of Sr,and therefore the catalysts had higher activity.Ba additives were more stable because of the addition of Sr,so that the catalysts had a better stability.The temperature of the secondary heat treatment had an impact on oxygen content of the support.With the heat treatment temperature increasing,the oxygen content of the support reduced.When the secondary heat treatment temperature was 1600 ?,the surface area and pore structure of the support were affected greatly.For K-Ru/AC catalysts,the activity and stability were affected adversely when the treated temperature was too high,and therefore the optimal treated temperature was 800 ?.For Ba-Ru/AC catalyst,the temperature of secondary heat treatment had a great effect on the activity of the catalyst.With the treatment temperature increasing,the initial activity of the catalyst decreased.However,the treated temperature had little effect on the stability of the catalyst,and the catalysts with different temperatures all had good thermal stability during the heating process.The support of Ba-Ru/AC catalysts did not have to carry out the secondary heat treatment.For K-Ba-Ru/AC catalysts,the temperature of the secondary heat treatment affected the initial activity of the catalysts.As the treated temperature increased,the initial activity of the catalysts decreased.The temperature of secondary heat treatment had little effect on the stability of the catalysts,the catalyst activity decreased during the heat process.But with the treated temperature increasing,the decreasing extent of activity of the catalysts reduced.