Influence of relative humidity on the photocatalytic oxidation (PCO) of toluene by TiO2 loaded on activated carbon fibers: PCO rate and intermediates accumulation
Influence of relative humidity on the photocatalytic oxidation (PCO) of toluene by TiO2 loaded on activated carbon fibers: PCO rate and intermediates accumulation
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DOI：
10.1016/j.apcatb.2007.09.033
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发表时间：
2008-02
影响因子：
22.1
通讯作者：
T. Guo;Z. Bai;Can Wu;Tan Zhu-
中科院分区：
文献类型：
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作者：
T. Guo;Z. Bai;Can Wu;Tan Zhu-
采用活性炭纤维（ACFs）负载TiO 2光催化剂，在环境条件控制箱中对甲苯进行了光催化氧化（PCO）实验。制备了TiO 2/ACF催化剂，用N2吸附等温线和扫描电镜（SEM）分别对催化剂的孔结构和形貌进行了表征。通过考察不同相对湿度（RH）条件下TiO 2/ACF催化剂上甲苯残留量和中间产物的种类、数量及其变化过程，探讨RH对甲苯PCO的影响以及水蒸气在PCO过程中的作用：PCO反应途径和中间产物在TiO 2/ACF催化剂上的积累。结果表明：（1）随着室内相对湿度的增加，（15%，30%，45%和60%）在所有RH条件下，甲苯的PCO转化率均呈正相关，且未观察到催化剂失活;（2）在甲苯气固PCO过程中，芳环氧化副产物2-甲基、对苯醌和邻（间，在TiO_2/ACF催化剂上观察到了对甲酚的侧链氧化反应，发现了苯甲醇、苯甲醛、苯甲酸等侧链氧化反应的中间产物;（3）尽管在所有RH条件下苯甲醛都是主要中间体，随着相对湿度的增加，芳环氧化副产物的量增加;（4）相对湿度的增加，苯甲醇的积累量增加，但苯甲醛的积累量减少。结果表明：（1）相对湿度影响甲苯的PCO速率和PCO反应路径，（2）虽然甲苯的PCO反应以甲基氧化为主，但随着相对湿度的增加，甲苯的PCO反应主要以芳香环氧化为主;（3）TiO_2除使水产生羟基自由基（OH）外，水分子也直接参与PCO过程。有人提出了一种假说：在PCO从苯甲醛到苯甲酸的转化过程中，存在由苯甲醛、羟基和水分子组成的过渡物种，但这一假说尚未得到证实。
Photocatalytic oxidation (PCO) tests were carried out for toluene adsorbed on the activated carbon fibers (ACFs)-supported TiO2photocatalyst in an environmental condition controlled chamber. TiO2/ACF catalyst was made and characterized by N2adsorption isotherm for pore structure and scanning electron microscopy (SEM) for morphology, respectively. Through exploring the remnant of toluene and the accumulation of intermediates on the TiO2/ACF catalyst including species, amount and their change processes under different relative humidity (RH), this study aimed to explore the influence of RH on the PCO of toluene and the roles of water vapor in the PCO process: PCO reaction paths and the accumulation of intermediates on the TiO2/ACF catalyst. Results showed that (1) with the increase of RH in the chamber (15%, 30%, 45% and 60%) the PCO conversion rate of toluene was positive correlated and no catalyst deactivation was observed under all RH levels; (2) during the gas–solid PCO process of toluene, byproducts of aromatic ring oxidation including 2-methyl, p-benzoquinone and o(m, p)-cresol were observed on the TiO2/ACF catalyst which had not been reported, together with the intermediates of side chain oxidation including benzyl alcohol, benzaldehyde and benzoic acid which had been reported; (3) although benzaldehyde was the primary intermediate under all RH level, amounts of the byproducts of aromatic ring oxidation were increased with the increase of RH; and (4) elevated RH increased the accumulation of benzyl alcohol but assuredly decreased the accumulation of benzaldehyde. These results suggested that (1) RH affects both the PCO rate and the PCO reaction path of toluene; (2) although methyl group oxidation is the major path, aromatic ring oxidation, which is not the expected path for the PCO of toluene, is enhanced when the RH increases; (3) apart from the role of hydroxyl radical (OH) produced from water by TiO2, water molecule also directly takes part in the PCO process. A hypothesis has been suggested: transition species comprised of benzaldehyde, hydroxyl and water molecule exists in the PCO conversion process from benzaldehyde to benzoic acid, though the hypothesis has not been confirmed.