摘要
以典型气态探针分子及骨架含高分散非毗邻过渡金属(Ti,Fe)的沸石分子筛材料(TS-1,HZSM-5)、半导体二氧化钛(P25)为考察对象,拟通过沸石分子筛对不同探针分子所表现的迥异光催化行为揭示催化材料本征物化结构、吸附特性、活性位类型对光催化行为的影响规律.催化材料表征及所获得的气相光催化反应结果表明:沸石分子筛(TS-1,HZSM-5)上的光催化氧化-还原反应主要通过表面金属-氧结构单元的电荷转移激发态实现;源于独特MFI拓扑孔道结构的优异吸附能力、特殊表面活性位分布环境及不同的光生电子-空穴分离机制,使得具规整分子级孔窗的TS-1及HZSM-5对三氯甲烷的光催化降解效率与活性稳定性远高于传统二氧化钛光催化剂;对单碳分子甲醇及含仲碳醇羟基异丙醇的光催化反应中,上述沸石分子筛则表现异常突出的选择性氧化特征,对终端产物甲醛及丙酮均具较高的转化效率和选择性.本文的反应设计路径及选择性氧化结果,可为高分散过渡金属修饰沸石分子筛在有机小分子的光催化转化上提供思路借鉴.
In this study, we selected zeolite molecular sieves （TS-I and HZSM-5） with highly dispersed transition metal （Ti or Fe） in their frameworks and TiO2 P25 as photocatalysts and typical gas as probe molecules. The structure and crystalliza-tion, specific surface area, pore size distribution, light absorption and active radical species were characterized by X-ray dif fraction （XRD）, Brunauer-Emmett-Teller surface area （BET）, diffuse reflectance spectroscopy （DRS） and electron spin reso nance spectroscopy （ESR）. The influences of the intrinsic structure, adsorption property and the kind of active sites of the catalytic materials on their photocatalytic behaviors of different molecules were investigated. The emphases were placed on the photocatalytic conversion of hydrophobic halohydrocarbons and hydrophilic lower alcohol over zeolite molecular sieves. The photocatalytic reactions were performed in a tubular vessel microreactor operating in a continuous-flow mode under UV irradiation. Analysis of the reactor effluent was conducted by a gas chromatograph （HP6890）. The concentrations of gas molecules and carbon dioxide were determined by using the flame ionization detector （FID） and thermal conductivity detec tor （TCD）, respectively. Under UV irradiation, the excited state between the isolated and highly dispersed Fe3＋/Ti4＋and bridging oxygen atom can activate the molecular oxygen into superoxide radical via the surface electron transfer, which can participate in the subsequent selective oxidation reactions. Due to zeolites with excellent adsorption relative to their unique MFI pore structure, active sites environment and the separation mechanism of photogenerated holes and electrons, these re sulted that TS-1 and HZSM-5 zeolites with regular pore structure of molecular dimensions showed good degradation rate of chloroform （about 80%） for 16 h, obviously higher than that of TiO〉 Also, they exhibited excellent selectivity for photocata lytic oxidation of methanol and isopropanol into formaldehyde and acetone, respectively. This is different from TiO2 as a typical representative of conventional semiconductor photocatalysts, in which the hydroxyl radicals with strong oxidation were produced as main active species and can mineralize the organic compounds into inorganic small molecules completely. This study provides ideas for the photocatalytic transformation of small organic molecules over molecular sieves with highly dispersed transition metal.
出处
《化学学报》
SCIE
CAS
CSCD
北大核心
2013年第10期1404-1410,共7页
Acta Chimica Sinica
基金
国家973前期研究专项(973
No.2011CB612314)
国家自然科学基金(No.21077023)
福建省自然科学基金(Nos.2010J01035
JA10008及JK2011001)资助~~
