Oxygen reduction in acidic media catalyzed by pyrolyzed cobalt macrocycles dispersed on an active carbon: The importance of the content of oxygen surface groups on the evolution of the chelate structure during the heat treatment
Oxygen reduction in acidic media catalyzed by pyrolyzed cobalt macrocycles dispersed on an active carbon: The importance of the content of oxygen surface groups on the evolution of the chelate structure during the heat treatment
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DOI：
10.1016/s0013-4686(97)00209-0
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发表时间：
1998
影响因子：
6.6
通讯作者：
P. Gouérec;M. Savy;J. Riga
中科院分区：
文献类型：
--
作者：
P. Gouérec;M. Savy;J. Riga
在之前的工作中，研究了热处理温度（500 ~ 900℃）对两种钴大环（CoTMPP和CoTAA）在表面氧基团含量高的活性炭上的负载的影响[1,2]。利用两种表面分析光谱（XPS和ToF SIMS）确定了螯合物的结构构型，并设置了在不同温度范围内相应的电化学活性的相关性。本文的目的在于了解在热处理过程中碳表面含氧基团含量的作用及其对螯合物热演化的影响。通过XPS分析考察了经热处理沉积在脱氧活性炭上的CoTAA的热分解情况。XPS数据显示出更快的大周期分解和金属颗粒的出现。此外，当碳表面存在大量含氧基团时，可以检测到钴氧化物。还进行了电化学研究，以确定这种结构的催化行为（还原的选择性、活性和电极的老化）。结果表明：除800°C热处理催化剂外，活性较低，失活率较高。本研究的主要结论是，活性炭表面大量的含氧基团可以保护螯合结构免受快速破坏和烧结行为，从而导致较慢的老化过程。
In previous work the influence of heat treatment temperatures (from 500 to 900°C) on two cobalt macrocycles (CoTMPP and CoTAA) support on active carbon with a high content of oxygen surface groups has been investigated [1,2]. The structural configuration of the chelates has been defined by applying two surface analysis spectroscopies (XPS and ToF SIMS) and setting on correlations with the corresponding electrochemical activity for different ranges of temperatures. The aim of this paper lies in the understanding of the role of the oxygenated groups content present at the carbon surface during the heat treatment process and its influence on the chelate thermal evolution. The thermal decomposition of CoTAA, which has been deposited and heat treated onto the previously deoxygenated active carbon was investigated through XPS analysis. The XPS data exhibit a faster decomposition of the macrocycle and the appearance of metallic particles. Moreover when large amounts of oxygenated groups were present on the carbon surface, cobalt oxides were detected. Electrochemical studies were also conducted to qualify the catalytic behavior of such structures (selectivity of the reduction, activity and ageing of the electrodes). Different results were observed compared to those reported in: lower activities and higher deactivation process (except for the 800°C heat treated catalysts) were found. The main conclusion in the present work resides in the fact that large amounts of oxygenated groups on the surface of the active carbon can protect the chelate structure from rapid destruction and sintering behavior and thereby lead to a slower ageing process.