活性炭及表面性质对Ru基氨合成催化剂性能的影响

 采用N2物理吸附和He-TPD等表征手段考察了不同活性炭及其经HNO3和氧化处理后的孔结构性质及表面基团的变化,并用CO化学吸附分析了其对活性组分Ru分散度的影响. 结果表明,活性炭较发达的中孔结构可显著提高Ru的分散度. 活性炭的部分表面含氧基团是Ru的分散中心,它们的量会明显影响催化剂的Ru分散度及活性. 活性炭经HNO3处理虽然可以使含氧基团的量增加,但同时也使不稳定基团的量增加,这些不稳定基团在催化剂还原过程中分解,不利于Ru的分散. 活性炭的气相热处理可以调变其表面结构及表面基团,从而提高 Ru的分散度及催化剂活性.

Effect of Activated Carbon and Its Surface Property on the Activity of Ru/AC Catalyst

Activated carbons (AC) were pretreated by washing with HNO 3 and calcination before the preparation of Ru/AC ammonia synthesis catalysts. The structure, texture and surface oxygen groups of the samples were investigated by N 2 physisorption and He-TPD, and their effect on the Ru dispersion was studied by CO chemisorption as well as on catalytic activity by activity test. The result showed that a more developed texture of the carbon support resulted in a higher dispersion of Ru metal. Furthermore, part of the surface oxygen groups was the centers of Ru deposition, their amount affected the dispersion of Ru and the activity of catalyst. HNO 3 treatment of activated carbon led to the great increase in surface oxygen groups, but some of the surface oxygen groups were unstable and decomposed into CO and CO 2 during the catalyst reduction. Thus Ru metal deposited on them will assemble, which is unfavorable for Ru dispersion. Although the Ru dispersion was not improved after HNO 3 treatment, the catalytic activity was increased from 17.4% to 18.4% because of the reduction of S and ash. Gas-phase oxidation of carbon changed its texture and surface groups significantly. So the Ru dispersion and catalytic activity were improved from 43% to 62% and 17.4% to 19%, respectively.