Development of catalytic system with nano-cluster catalyst for restoration of ground water polluted by nitrate

地下水硝酸盐(NO3-)污染是一个普遍存在的问题，因为过量摄入硝酸盐会导致婴儿蓝婴综合症、糖尿病和癌症。主要来源是农业实践(化肥和牲畜排泄物)，地下水的修复是迫切需要解决的问题。在生物处理、离子交换、反渗透等方面还存在很多问题。近年来，NO_3~(2-)催化加氢制取N_2受到了广泛的关注。对于硝酸盐、亚硝酸盐(NO2-)和NH3，有害组分的含量必须降低到最大允许水平，分别为50、0.1-3和0.5ppm。我们发现，在高pH条件下，活性碳负载的Cu-Pd团簇对NO3-加氢生成NO2-具有很高的选择性。另一方面，Pd交换的β沸石选择性催化NO2-加氢生成N_2和N_2O。从这些发现中，我们受到了一个两阶段过程的启发，该过程允许催化剂为每个阶段进行优化；NO_3^-氢化…更多的是第一阶段的NO_2^-和第二阶段的NO_2^-加氢。本文报道了由铜-钯簇合物/AC和钯/β沸石组成的两段工艺在净化受水污染的硝酸盐废水中的应用前景。需要强调的是，在298K和288K时，NH3的浓度分别只有0.7和0.6ppm，非常接近饮用水的允许值(0.5ppm)。然后针对单一催化剂的饮用水一段工艺，寻找出具有良好的活性、选择性和稳定性的2wt%Pd-1.2wt%Cu/丝光沸石(Si/Al=37)对N_2和N_2O具有高度选择性的催化剂，离子交换法制备的Cu-Pd/丝光沸石催化剂在278-333K温度下表现出较强的稳定性。近年来，从Pd-Cu团簇制备的Pd-Cu/疏水AC催化剂被发现具有高活性和选择性，即对氨气的生成有很大的抑制作用。此外，该催化剂即使在硫酸根离子和氯离子存在的情况下也能工作。较少

Pollution of groundwater with nitrate (NO_3^-) is a widespread problem, since excess intake of nitrate causes blue baby syndrome for infants and diabetes and cancers. The major sources are agricultural practices (fertilizers and excretions of livestock), and the remediation of groundwater is urgent issue. The biological treatment, ion exchange, and reverse osmosis have still much issues. Recently catalytic hydrogenation of NO_3^-to N_2 have attracted much attention. It is necessary to reduce the levels of harmful components to the maximum allowable levels, 50, 0.1-3, and 0.5 ppm for nitrate, nitrite (NO_2^-), and NH_3.We found that Cu-Pd clusters supported on active carbon are highly selective for the hydrogenation of NO_3^- to NO_2^- at high pH. On the other hand, Pd exchanged beta zeolite catalyzed selectively the hydrogenation of NO_2^- to N_2 and N_2O. From these findings, we were inspired in a two-stage process which allows catalysts optimized for each stage ; NO_3^-hydrogenation … More to NO_2^-in the first stage and NO_2^-hydrogenation in the second stage. Here we wish to report that the two-stage process consisting of Cu-Pd cluster/AC and Pd/beta-zeolite is promising for the purification of water contaminated nitrate. It should be emphasized that the concentration of NH_3 was only 0.7 and 0.6 ppm at 298 and 288 K, respectively which are very close to the allowable value (0.5 ppm) for drinking water.Then a one-stage process aimed at drinking water using a single catalyst, the catalyst with acceptable activity, selectivity, and stability for the practical use is searched 2wt%Pd-1.2wt%Cu/mordenite (Si/Al=37) was highly selective to N_2 and N_2O, depressing NH_3 (5 ppm from 200 ppm of nitrate) and exhibited robust stability at 278-333 K. Cu-Pd/mordenites that were prepared by ion-exchange method. Recently, Pd-Cu/hydrophobic AC catalysts prepared from Pd-Cu cluster exhibited was found to be high active and selective, that is, be greatly suppressed for the formation of ammonia. Furthermore, this catalyst has worked even in the presence of sulfated ion and chloride ion. Less