Photocatalytic oxidation of toluene at indoor air levels (ppbv): Towards a better assessment of conversion, reaction intermediates and mineralization
Photocatalytic oxidation of toluene at indoor air levels (ppbv): Towards a better assessment of conversion, reaction intermediates and mineralization
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DOI：
10.1016/j.apcatb.2008.08.003
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发表时间：
2009-02
影响因子：
22.1
通讯作者：
M. Sleiman;P. Conchon;C. Ferronato;J. Chovelon
中科院分区：
文献类型：
--
作者：
M. Sleiman;P. Conchon;C. Ferronato;J. Chovelon
我们在这里报告了一种新的分析方法，用于研究室内相关浓度水平 (ppbv) 下的甲苯光催化去除。实验采用环形流通式反应器，以TiO2为光催化剂，以甲苯为模型VOC，在不同范围的相对湿度（RH：0-70%）、入口浓度（20-400ppbv）和流量（70-350mLmin−1）下进行。使用与 GC-MS 仪器 (ATD-GC-MS) 联用的自动热解吸技术对反应中间体进行分析，而与脉冲放电氦电离检测器 (GC-PDPID) 联用的 GC 首次用于在线测量 ppbv 水平的 CO 和 CO2。在这些条件下，甲苯转化率高达 90-100%，入口浓度和相对湿度的影响很小，而流量是一个普遍因素。矿化（%）从 55% 到 95% 不等，并且已被证明受到 RH 增加的强烈抑制，而流速和入口浓度的影响可以忽略不计。发现反应中间体根据相对湿度的不同而不同：在没有水蒸气的情况下，在气相中检测到痕量的低分子量羰基化合物（甲醛、甲基乙二醛等），而在相对湿度为40%时，观察到羟基化的中间体，例如甲酚和苯甲醇。根据鉴定结果，提出了一种反应机理，主要涉及干燥条件下的直接空穴氧化和高RH条件下的OH自由基羟基化。
We report here a new analytical methodology for the investigation of toluene photocatalytic removal at indoor-relevant concentration level (ppbv). Experiments were performed using an annular flow-through reactor with TiO2as photocatalyst, toluene as a model VOC and under different ranges of relative humidity (RH: 0–70%), inlet concentration (20–400ppbv) and flow rate (70–350mLmin−1). Analysis of reaction intermediates was conducted using an automated thermal desorption technique coupled to GC–MS instrument (ATD–GC–MS) whereas a GC coupled to pulsed discharge helium ionization detector (GC–PDPID) was used for the first time for on-line measurements of CO and CO2at ppbv level. Under these conditions, toluene conversion was up to 90–100% with a slight influence of inlet concentration and RH, whereas flow rate was found to be a prevalent factor. Mineralization (%) varied from 55 to 95% and has shown to be strongly inhibited by the increase of RH whereas flow rate and inlet concentration exhibited a negligible effect. The reaction intermediates were found to be different according to the RH level: in absence of water vapor, traces of low molecular weight carbonyls (formaldehyde, methyl glyoxal, etc.) were detected and quantified in the gas phase whereas at RH 40%, hydroxylated intermediates such as cresols and benzyl alcohol were observed. On the basis of identification results, a reaction mechanism was proposed involving mainly direct hole oxidation at dry conditions and hydroxylation by OH radicals at high RH level.