用水合肼还原的Ru/AC氨合成催化剂的制备

Preparation of Ru/AC Ammonia Synthesis Catalyst Reduced with Hydrazine Hydrate

用RuCl3 水溶液浸渍BET比表面积为 1 0 2 0m2 / g的椰壳活性炭 (AC)载体 ,制备了钌含量为 6 %的Ru/AC氨合成催化剂 .在添加助剂前 ,分别用水合肼水溶液、水合肼蒸气和H2 还原催化剂 ,然后分别浸渍Ba(NO3 ) 2 和KOH .催化剂中的Ru∶K∶Ba摩尔比为 1∶3∶0 3.用N2 物理吸附、XPS和CO化学吸附等方法对催化剂进行了表征 .结果表明 ,用不同还原方法制备的催化剂上的钌以不同的化学状态存在 ,它的活性与其比表面积和金属钌的分散度相关 .用水合肼水溶液还原的催化剂S1 中的钌在大气气氛下以金属态存在 ,它的BET比表面积和金属分散度较大 ,低温低压下催化活性最高 .以水合肼蒸气还原的催化剂S2 中的钌在大气气氛下以RuO3 形态存在 ,它的BET比表面积和金属分散度小 ,催化活性最低 .用H2 还原的催化剂S3中的钌在大气气氛下以RuO2 形态存在 ,其BET比表面积和金属分散度与S1 催化剂相当 ,催化活性也与S1

The Ru/active carbon (AC) ammonia synthesis catalyst was prepared by the impregnation method using coconut ( A BET = 1?020 m 2/g) as the support. Firstly, AC was impregnated with RuCl 3 aqueous solution. Then the samples were reduced with hydrogen, hydrazine hydrate solution and hydrazine hydrate vapos, respectively. Subsequently, the three Ru/AC samples were impregnated with aqueous solution of barium nitrate and potassium hydroxide. The Ru content was 6% based on the AC mass and the molar ratio of Ru∶K∶Ba was 1∶3∶0 3 in these catalysts. The catalysts were characterized by XPS, N 2 adsorption and CO pulse chemical adsorption. The results showed that Ru was present in different chemical states in the three catalysts obtained with different reductants. The catalyst activity correlated with their surface area and Ru dispersion. The catalyst that was reduced with hydrazine hydrate solution at pH=10～13 in the range from room temperature to 90 ℃ for 20 min had the highest surface area of 942 m 2/g , Ru dispersion of 17 72% and catalytic activity of 20 36%(volume ratio of NH 3) at low pressure. In this catalyst Ru remained in the metallic state when the sample was exposed to atmosphere.