• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>Nanotechnology >The nature of 'overexchanged' copper and platinum on zeolites
【24h】

The nature of 'overexchanged' copper and platinum on zeolites

机译：沸石上“过度交换”的铜和铂的性质

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

The uptake of platinum and copper tetra-ammine (PTA and CTA, [(NH_3)_4Pt]~(2+) and [(NH_3)_4 Cu]~(2+)) into zeolites was compared over silica and three zeolites (Y, MOR and MFI) with different points of zero charge and aluminium content. Adsorption was determined as a function of pH at several metal concentrations, and pH shifts relative to metal free control experiments were carefully monitored. The uptake of both metal ammine complexes onto silica is well described by electrostatic adsorption. We suggest that the metal cations interact with zeolites by two mechanisms, ion exchange at the Al exchange sites and electrostatic adsorption at silanol groups. The former is the dominant mechanism at low to mid pH, and the latter at high pH. This effect is most clearly manifested in zeolites with low aluminium content such as ZSM5; electrostatic adsorption at high pH in ZSM5 yields metal loadings much in excess of the ion exchange capacity and so gives rise to 'overexchange'. Differences between PTA and CTA can be explained by the weaker stability of the CTA complex and its response to the decrease in local pH near the adsorption plane of low PZC zeolites. This change in local pH near oxide surfaces is characteristic of electrostatic adsorption. As the local pH decreases, the CTA ion is probably converted to a dimerized copper complex, perhaps Cu_2(OH)~(2+)_2. A portion of the released ammonia is protonated, increasing the solution pH. In high PZC, high aluminium zeolites with high ion exchange capacity, there is relatively little contribution from electrostatic adsorption.
机译：比较了二氧化硅和三种沸石（Y）对铂和铜四氨（PTA和CTA，[（NH_3）_4Pt]〜（2+）和[（NH_3）_4 Cu]〜（2+））沸石的吸收情况。 ，MOR和MFI）具有不同的零电荷和铝含量。确定吸附是几种金属浓度下pH值的函数，并仔细监测相对于无金属对照实验的pH值变化。通过静电吸附很好地描述了两种金属氨基配合物在二氧化硅上的吸收。我们建议金属阳离子通过两种机理与沸石相互作用，铝交换位点的离子交换和硅烷醇基团的静电吸附。前者是中低pH值的主导机制，后者是高pH值。这种效果最明显地表现在低铝含量的沸石（例如ZSM5）中。 ZSM5在高pH值下的静电吸附产生的金属负载量远远超过离子交换容量，因此会引起“过度交换”。 PTA和CTA之间的差异可以用CTA配合物的较弱稳定性及其对低PZC沸石吸附平面附近局部pH降低的响应来解释。氧化物表面附近局部pH的这种变化是静电吸附的特征。随着局部pH值的降低，CTA离子可能转化为二聚铜络合物，可能是Cu_2（OH）〜（2 +）_ 2。一部分释放的氨被质子化，从而增加了溶液的pH值。在高PZC，高铝离子交换能力的铝沸石中，静电吸附的贡献相对较小。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号