On the chemistry of the keggin Al13 polymer: kinetics of proton-promoted decomposition
On the chemistry of the keggin Al13 polymer: kinetics of proton-promoted decomposition
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DOI：
10.1016/s0016-7037(99)00234-3
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发表时间：
1999-10
影响因子：
5
通讯作者：
G. Furrer;M. Gfeller;B. Wehrli
中科院分区：
文献类型：
--
作者：
G. Furrer;M. Gfeller;B. Wehrli
用间歇式和流通式反应器研究了多核Keggin Al13物种(Al13O4(OH)24(H2O)127+或Al13)的分解与pH(2.06≤≤3.50)、离子强度(I=0.1和1.0)和温度(10°C≤T≤65°C)的关系。总的分解速率与H+的活度、离子强度和温度呈正相关，半衰期在350-43,000 S之间。分解速率被解释为两个平行反应的函数，对[H+]−d[A113]dt=r1+r2(1)，其中r1=k1[H+][al13]，r2=k2[H+]2[al13]。在25℃和i=0.1时，速率常数k1和k2分别为0.0333±0.0016 M−1s−1和2.59±0.62M−2s−1。离子强度为1.0时的活化能和阿累尼乌斯因子分别为Ea1=13.3±1.9kJmol−1，Ea2=44.9±4.9kJmoL−1，A1(I=1.0)=25.2±19.2M−1S−1，A2(I=1.0)=1.62109±3.12 109M−2S−1。得到I=0.1时的Arrhenius因子为：A1(I=0.1)=7.23±0.19M−1S−1和A2(I=0.1)=1.86 108±1.9 107M−2S−1。在不同离子强度下，根据Arrhenius因子计算了Al_(13)络合物与离子相遇时的表观电荷。我们假设具有质子化桥联羟基的Al13是分解反应的先驱，在[H+]中是一级的。前驱HAl138+的放热形成解释了单质子途径活化能低的原因。较大的Ea2值表明，具有两个相邻质子化中心的前驱体的形成包含一个正的反应热。PH为5时的半衰期为数百小时，表明天然水中可能存在Al13，但也可能发生持续的分解和重整。
The decomposition of the polynuclear Keggin Al13species (Al13O4(OH)24(H2O)127+or Al13) has been examined as a function of pH (2.06 ≤ pH ≤ 3.50), ionic strength (I = 0.1 and 1.0) and temperature (10°C ≤ T ≤ 65°C) using batch and flow-through reactors. The overall decomposition rates were found to be positively correlated with the activity of H+, ionic strength and temperature with half-lives ranging from 350 to 43,000 s. The decomposition rate was interpreted as a function of two parallel reactions, one first-order and one second-order with respect to [H+] − d[A113] dt =R1+R2(1) where R1= k1[H+] [Al13] and R2= k2[H+]2[Al13]. For 25°C and I = 0.1, the rate constants k1and k2were determined as 0.0333 ± 0.0016 M−1s−1and 2.59 ± 0.62 M−2s−1, respectively. The activation energies and the Arrhenius factors for an ionic strength of 1.0 were found to be Ea1= 13.3 ± 1.9 kJ mol−1, Ea2= 44.9 ± 4.9 kJ mol−1, A1(I=1.0)= 25.2 ± 19.2 M−1s−1, A2(I=1.0)= 1.62 109± 3.12 109M−2s−1. While Ea1and Ea2do not depend on the ionic strength, the Arrhenius factors for I = 0.1 were obtained as A1(I=0.1)= 7.23 ± 0.19 M−1s−1and A2(I=0.1)= 1.86 108± 1.9 107M−2s−1. The apparent charge of the Al13complex in the encounter reaction with a hydronium ion was calculated from the Arrhenius factors at various ionic strengths as 0.78. We postulate Al13with a protonated bridging OH group as the precursor for the decomposition reaction, first-order in [H+]. The low value of the activation energy for the one-proton pathway is explained by an exothermic formation of the precursor HAl138+. The larger value of Ea2indicates that the formation of a precursor with two adjacent protonated sites involves a positive reaction enthalpy. The half-life of several hundred hours at pH 5 indicates that Al13may exist in natural waters, however, it may also be subject to continuous decomposition and reformation.