Ag掺杂V2O5／TiO2催化氧化3-甲基吡啶脱甲基反应

Ag doped V_2O_5/ TiO_2 catalyst for oxidative dealkylation of 3-picoline

采用浸渍法制备了不同Ag掺杂的Ag-V/TiO_2催化剂,考察其催化部分氧化3-甲基吡啶脱甲基性能。采用X射线衍射(XRD)、X射线光电子能谱(XPS)、H_2程序升温还原(H_2-TPR)对催化剂进行了表征。结果表明,Ag的掺杂提高了催化剂中表面氧和+4价态的钒物种的含量,加快了催化剂的还原过程,提高了氧化活性,Ag主要以单质的形态存在。3-甲基吡啶氧化反应表明,Ag的掺杂使反应选择性发生变化,主产物由烟酸变成吡啶,当Ag的掺杂量为2%(Ag相对于V_2O_5的摩尔分数)时,甲基的脱除率最好,摩尔产率为80.1%,选择性84.7%,烟酸几乎不产生。该脱甲基氧化反应的过程是V^(4+)/V^(5+)(O_2^-)在攻击侧链的C—H键的同时,Ag在O_2的作用下形成了含有亲电子型氧(O^-和O_2^-)的Agp+O活性物种,攻击侧链和苯环相连的C—C键,共同作用将侧链的甲基以氧化形成CO_x的形式脱除。

The effect of silver loading on V2O5/TiO2 catalysts （Ag-V/TiO2）,prepared by impregnation method, on the oxidative dealkylation behavior of 3-picoline was investigated. The samples were characterized by X-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS） and H2 temperature- progranuned reduction （H2-TPR）. It was found that Ag was contributed to promotion of the formation of surface oxygen species and change of the valence of vanadium species （ V4 ＋/V5 ＋ ） through interaction of V and Ag, shortened the time of reduction process, increased the oxidative activity. Thus, the selective oxidation of methylarene were modified over the Ag-V/TiO2 catalysts, which pyridine as the main product was found with few nicotinic acid. At optimum loading of 2% Ag（ mole fraction base on V205 ） was found to enhance the catalytic performance in terms of mole yield （80. 1% ） and selectivity （84. 7% ）. Additionally, Ag highly dispersed on the catalysts as atom, which could formed silver oxide （Ago ＋ O oxygen species：O- , O2 ） by adosorbed the Oz. An oxidative mechanism was eonjectured：C--H bond was activated by V4 ＋/V5 ＋ （ oxygen species ： O2- ） and Agp ＋ 0 absorbed on the C--C bond because of the 0 - and O2- were strong electrophilic reactants, which attacted the site of high charge density of reacted molecule, causing the C--C bond to decompose ,--CH3 was oxidatived to form COS.