生物质衍生Fe-N-C多孔炭材料的制备及其对硝基苯的催化还原性能

Preparation of Biomass-derived Fe-N-C Porous Carbon Material and Its Catalytic Reduction of Nitrobenzene

以价格低廉的杉木屑为原料,与尿素和FeCl_(3)·6H_(2)O按照质量比1∶1∶2混合,在700~1000℃下炭化制备负载铁的氮掺杂多孔炭材料(Fe-N-C)。对不同温度下所制备炭材料的元素组成、结构和表面化学等进行分析,并考察其对硝基苯的催化还原性能。研究结果表明:炭化温度对负载铁和掺杂氮物种有显著影响,700℃时制备的多孔炭材料(Fe-N-C-700)中铁物种主要为Fe_(3)O_(4),氮物种主要为吡啶氮和吡咯氮,随着温度升高铁物种主要以金属铁为主,同时部分吡啶氮转变为石墨氮。当温度为900℃时,所制备的多孔炭材料(Fe-N-C-900)含铁量为43.42%,含氮量为2.19%,其中石墨氮37.7%,吡啶氮23.8%,吡咯氮22.9%,氧化氮15.6%,在55℃下反应2.5 h时催化还原硝基苯的转化率和选择性接近100%,这与Fe-N-C-900负载的金属铁和石墨氮之间的协同作用有关。当Fe-N-C-900催化还原带有给电子基团如甲基、氨基、羟基的硝基芳烃时,能够以较高的转化率和选择性得到相应产物。此外,当硝基芳烃上带有吸电子基团如氯、碘时,反应时间需要延长至4 h,反应物转化率可以达到97.3%以上,生成的产物选择性大于99%,表明Fe-N-C-900对不同底物表现出良好的普适性。此外,利用该催化剂的磁性对其进行回收,循环使用5次后,催化性能没有明显降低,硝基苯的转化率仍达到98.3%,产物选择性为96.5%,展现出良好的稳定性。

Fir sawdust,urea and FeCl_(3)·6H_(2)O were mixed thoroughly at a mass ratio of 1∶1∶2 to generate the nitrogen doped porous carbon materials loaded with iron(Fe-N-C)after annealing the mixtures at the temperature of 700-1000℃.The elemental composition,structure and surface properties of the obtained carbon materials at different temperatures were analyzed.Following that,the catalytic performance of the reduction of nitrobenzene were investigated.The results showed that the carbonization temperature had a significant effect on the iron and doped nitrogen species.At 700℃,the iron species in Fe-N-C-700 were mainly Fe_(3)O_(4),whereas the nitrogen species were mainly pyridinic-N and pyrrolic-N.As the temperature rose,the iron species became mostly metallic iron,and a portion of the pyridinic-N was changed to graphitic-N.When the temperature was 900℃,the manufactured porous carbon material(Fe-N-C-900)had a Fe content of 43.42%and a N content of 2.19%,of which the graphitic-N was 37.7%,pyridinic-N was 23.8%,pyrrolic-N was 22.9%and oxidized-N was 15.6%.When the reaction duration was 2.5 h at 55℃.The conversion and selectivity of catalytic reduction of nitrobenzene were close to 100%.The high catalytic performance of Fe-N-C-900 might be due to the synergistic effect between the high content of iron species and graphite nitrogen formed during the calcination process.When Fe-N-C-900 was used for catalytic reduction of nitroarenes with electron-donating substituents such as methyl,amino or hydroxyl group,the corresponding products might be produced with high conversion and selectivity.In additon,when the nitroarenes contained electron-withdrawing substituents such as chlorine or iodine group,the reaction time must be extended to 4 h,and the conversion rate could reach up to 97.3%with the product selectivity above 99%.It indicated that Fe-C-N-900 had good universality for various substrates.And the catalyst had good stability and magnetic recyclability.After 5 times of recycling,the catalytic performance did not decrease obviously,the nitrobenzene conversion remained at 98.3%with the selectivity of 96.5%.