Development of porous nano-structured materials with heterojunction structure and application to low temperature de-NOx catalysts

为制备高分散贵金属多孔催化剂，研究了水滑石(HT)Mg_&lt；0.74&gt；Al_&lt；0.26&gt；(OH)_2(NO_3)_&lt；0.26&gt；，的阴离子交换性能。在用PtCl6^&lt；2-gt；和PdCl4^&lt；2-&gt；进行阴离子交换时，XAFS分析表明，HT层间的配体被NO3^-部分取代。在H_2气流中加热时，硝酸根被还原成N_2，由此形成的空位可以被层间的NO_3^-占据。层间贵金属的这种催化作用有利于NO_3~(2-)从层间空间的去除，从而将层状结构转化为多孔骨架。在70℃时，铂-羟色胺催化剂的NOx转化率为82%，而负载型铂/氧化镁催化剂需要更高的温度90℃，才能获得87%的NOx转化率。与负载型Pd/MgO催化剂相比，Pd-HT催化剂在较低的温度下具有更高的NOx转化率。因此，铂-羟色胺纳米复合材料…在过量O_2存在下，低温NO-H_2反应具有更多的催化剂活性。另一方面，在70℃下，在过量O_2存在下，使用0.1%NO，0-10%O_2，铂|Nafion|铂，H_2O的电化学池，成功地实现了NO还原为N_2/N_2O。H^+导电的固体聚合物电解质(SPE)在铂阴极析氢过程中起着关键作用，催化NO-H_2发生在电极上。结果表明，由于铂表面覆盖了稳定的硝酸盐(NO3)物种，阻碍了氧在铂表面的吸附，从而抑制了H_2-O_2竞争反应。对H_2-O_2反应的抑制作用在[小于或等于]100℃时最有效，这与固相萃取的最佳操作温度范围一致。在阴极室中填充1wt%的铂/ZSM-5催化剂可提高富氧条件下NO的还原效率。SPE电池与铂催化剂的结合可广泛应用于强氧化性气氛下的新型低温脱氮工艺。较少

The anion exchange property of hydrotalcite(HT),Mg_<0.74>Al_<0.26>(OH)_2(NO_3)_<0.26>, was studied for the preparation of porous catalysts containing highly dispersed noble metals. In the anion exchange using complexes, PtCl_6^<2-> and PdCl_4^<2->, partial replacement of the ligand with NO_3^- in the HT interlayer occurred as was revealed by XAFS analysis. On heating in a H_2 flow, the nitrate ligand would be reduced to evolve N_2 and the vacant site thus formed can subsequently be occupied by NO_3^- in the interlayer. Such a catalytic role of interlayer noble metals facilitates the removal of NO_3^- from the interlayer space and thus converts the layered structure into a porous framework. The Pt-HT catalyst allowed 82% NO_x conversion at 70℃, whereas a supported Pt/MgO required higher temperature 90℃ where 87% NO_x conversion was obtained. Similarly, Pd-HT catalyst allowed higher NO_x conversion at the lower temperature compared with a supported Pd/MgO catalyst. Thus, Pt-HT nanocompos … More ites were found to be active for the low temperature NO-H_2 reaction in the presence of excess O_2.On the other hand, the reduction of NO to N_2/N_2O in the presence of excess O_2 has been successfully achieved at 70℃ using an electrochemical cell of the type,0.1% NO,0-10% O_2,Pt |NAFION| Pt,H_2O. An H^+-conducting solid polymer electrolyte(SPE) plays a key role in evolving hydrogen on the Pt cathode, where the catalytic NO-H_2 takes place. It was revealed that the competitive H_2-O_2 reaction is suppressed because the Pt surface was covered with stable nitrate(NO_3) species, which blocks oxygen adsorption hereon. The inhibition of H_2-O_2 reaction becomes most efficient at 【less than or equal】100℃ in agreement with the optimal operation temperature range of SPE. The reduction efficiency of NO in an excess O_2 could be improved by packing 1 wt% Pt/ZSM-5 catalyst in the cathode room. The combination between the SPE cell and Pt catalysts can broadly be applied to novel low-temperature deNOx processes in a strongly oxidizing atmosphere. Less