Selective hydrogenation of nitrate to nitrite in water over Cu-Pd bimetallic clusters supported on active carbon
Selective hydrogenation of nitrate to nitrite in water over Cu-Pd bimetallic clusters supported on active carbon
复制标题
DOI：
10.1016/j.molcata.2006.01.041
复制
发表时间：
2006-05
影响因子：
--
通讯作者：
Yoshinori Sakamoto;Y. Kamiya;T. Okuhara
中科院分区：
文献类型：
--
作者：
Yoshinori Sakamoto;Y. Kamiya;T. Okuhara
在333K下，采用气液并流法考察了活性碳负载的铜-钯簇合物在水中加氢硝酸盐(200ppm)的反应。用聚乙烯吡咯烷酮(PVP)和柠檬酸钠(SC)稳定的两种铜-钯双金属簇合物表明，当反应器出口pH为10.5时，催化剂对亚硝酸盐具有相似的活性(单位Pd质量)和高选择性。PVP稳定的簇合物/AC对亚硝酸盐的高选择性受铜/钯原子比(=0.5~4.0)的影响最小，当原子比为1：1时，活性最高。通过加入氢氧化钠将pH值提高到12.4，使SC稳定的Cu0.63-Pd簇合物/AC对亚硝酸盐的选择性提高到93%，但反应速度有所下降。在Cu0.63-Pd团簇/AC催化剂上，在pH值为10.5时，亚硝酸盐的加氢反应比硝酸盐的加氢反应慢得多，这表明OH-−抑制了亚硝酸盐的吸附，从而获得了对亚硝酸盐的高选择性。X-射线衍射仪和扫描电子显微镜表明，在AC上生成的Cu0.63-Pd团簇的尺寸为4 nm，反应过程中团簇的结构基本保持不变。Cu0.63-Pd/AC的活性和选择性优于Cu0.63-Pd的活性和选择性。此外，Cu0.63-Pd簇合物/AC比常规制备的Cu0.63-Pd/AC具有更高的活性和选择性，表明Cu0.63-Pd簇合物是硝酸盐加氢制亚硝酸盐选择性催化剂的优良前驱体。
Hydrogenation of nitrate (200ppm) in water with H2over Cu-Pd clusters supported on active carbon (AC) was investigated at 333K using a gas–liquid co-current flow system. Two types of Cu-Pd bimetallic clusters, stabilized with either poly(vinylpyrrolidone) (PVP) or sodium citrate (SC), revealed that the catalysts possessed similar activity (per unit weight of Pd) and high selectivity toward nitrite when pH was 10.5 at the outlet of the reactor. The high selectivity toward nitrite on PVP-stabilized cluster/AC was minimally influenced by the atomic ratio of Cu/Pd (=0.5–4.0); activity was maximal at a ratio of 1:1. Increasing pH to 12.4 by addition of NaOH enhanced the selectivity toward nitrite to 93% over SC-stabilized Cu0.63-Pd cluster/AC, but caused a decrease in the reaction rate. Over Cu0.63-Pd cluster/AC, hydrogenation of nitrite as an intermediate occurred much more slowly than that of nitrate at pH 10.5, suggesting that high selectivity toward nitrite is attained by OH−inhibiting adsorption of nitrite. XRD and STEM gave the size of the Cu0.63-Pd cluster on AC as 4nm; the structure of the cluster remained almost unchanged during the reaction. The activity and selectivity of the Cu0.63-Pd cluster/AC was superior to those of the Cu0.63-Pd cluster on oxides such as TiO2, Al2O3, and ZrO2. In addition, the Cu0.63-Pd cluster/AC was more active and selective than conventionally prepared Cu0.63-Pd/AC, indicating that the Cu-Pd cluster is an excellent precursor for selective catalysts in the hydrogenation of nitrate to nitrite.