MOLECULAR ADSORPTION-DESORPTION REACTIONS OF AMMONIA ON ALKALI-HALIDE CLUSTERS AND NANOCRYSTALS

被引：11

作者：

HOMER, ML ^{[1
]}

LIVINGSTON, FE ^{[1
]}

WHETTEN, RL ^{[1
]}

机构：

[1] UNIV CALIF LOS ANGELES,DEPT CHEM & BIOCHEM,LOS ANGELES,CA 90024

来源：

JOURNAL OF PHYSICAL CHEMISTRY | 1995年 / 99卷 / 19期

关键词：

D O I：

10.1021/j100019a046

中图分类号：

O64 [物理化学（理论化学）、化学物理学];

学科分类号：

070304 ; 081704 ;

摘要：

The initial adsorption of ammonia molecules (NH3) on larger alkali halide clusters and small nanocrystals (mainly NaF) has been investigated by flow-reactor methods as a function of cluster size and temperature. An analysis of the strong size-dependent reactivity of positively-charged NaF clusters, along with their computed structures, indicates that a particular type of defect in the nanocrystal structure facilitates adsorption. This defect is formed by removing an ion-pair from adjoining face and internal sites of a perfect crystallite, creating a basket-like opening. KF nanocrystals show very similar reactivity patterns, reflecting their corresponding structures, but LiF clusters follow a different pattern. It was established that NH3 adsorption on preformed NaF nanocrystals takes place under equilibrium conditions. The equilibrium constant for initial adsorption-desorption increases with decreasing temperature (250-340 K) and allows one to derive heats of NH3 adsorption near 0.2 eV for the more reactive (defective) nanocrystals. The much lower reactivity of negatively-charged clusters is ascribed to an additional kinetic-dynamic barrier to adsorption.

引用

页码：7604 / 7612

页数：9

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