Ag掺杂V2O5/TiO2催化氧化3-甲基吡啶 脱甲基效应

Ag doped V2O5/TiO2 catalyst for oxidative dealkylation of 3-picoline

摘要:

浸渍法制备了不同Ag掺杂的Ag-V/TiO2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），H2程序升温还原（H2-TPR）对催化剂进行了表征。表征表明，Ag的掺杂提高催化剂中表面氧和 4价态的钒物种的含量，有效的加快了催化剂的还原过程，提高了氧化活性。3-甲基吡啶氧化反应表明，Ag掺杂使反应选择性发生根本性变化，主产物由烟酸变成吡啶，选择性84.7%，烟酸几乎不产生。该脱甲基氧化反应的过程是V4 /V5 （O2-）在攻击侧链的C-H键的同时Ag在O2的作用下形成了含有亲电子型氧（O-和O2-）的Agp O活性物种，攻击侧链和苯环相连的C-C键，Ag和V共同作用将侧链的甲基以氧化形成COx的形式脱除。

Abstract:

The effect of silver (Ag) loading on titanium-supported vanadium (Ag-V/TiO2) catalysts, prepared by impregnation method, on the oxitative dealkylation behavior of 3-picoline has been investigated. At optimum loading of 2mol % Ag was found to enhance the catalytic performance in terms of yield (80.1%) and selectivity (84.7%). As evidenced by X-ray photoelectron spectroscopy (XPS) and H2 temperature-programmed reduction (H2-TPR), Ag is attributed to promotion of the formation of surfance 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. Additionally, Ag highly dispersed on the catalysts as atom, which could formed silver oxide (Agp O oxygen species: O-, O2- and O2-) by adosorbed the O2. 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.An oxidative machnism was conjectured: C-H bond was activited by V4 /V5 (oxygen species: O2-) and Agp O absorbed on the C-C bond because of the O- 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 COx.