氧-氮等离子体表面改性石墨烯用于肉桂醛水相加氢反应

Oxygen-ammonia plasma surface modified graphene for aqueous hydrogenation of cinnamaldehyde

使用等离子体表面改性技术对石墨烯(GR)进行处理,通过优化气源、放电功率、放电时间和工作气压,制备了具有两亲表面的氮掺杂GR(NDGR),以其为载体制备了Pt纳米催化剂(Pt/NDGR)。采用FTIR、Raman、元素分析仪、TEM和光学接触角测量仪对催化剂进行了表征,并评价了其对肉桂醛(CAL)水相加氢反应的催化性能。结果表明,采用等离子体两步接枝工艺,即先以O_(2)为等离子体气源活化GR表面,再以NH_(3)为等离子体气源在GR表面接枝含氮基团得到的氮掺杂GR[NDGR(O_(2)-NH_(3))]具有最佳的表面性质。与GR负载Pt催化剂(Pt/GR)相比,在放电功率140 W、工作气压200 Pa、放电时间6 min的最佳条件下制备的NDGR(O_(2)-NH_(3))负载Pt催化剂[Pt/NDGR(O_(2)-NH_(3))]在CAL水相加氢反应中显示出优良的催化性能。在80℃、3MPa、Pt/NDGR(O_(2)-NH_(3))为催化剂、4 h的反应条件下,CAL的转化率达98%,肉桂醇的选择性约为84%,反应速率常数为(1.072±0.051)h^(–1),远高于Pt/GR为催化剂的(0.624±0.023)h^(–1);其反应活化能约为14 kJ/mol,仅为Pt/GR为催化剂的(约29k J/mol)的48.3%。Pt/NPGR(O_(2)-NH_(3))的高催化性能得益于GR表面接枝少量含氮基团后Pt纳米粒子锚定位点的增加、对底物的高吸附性能以及金属-载体间协同作用。

Nitrogen doped graphene(NDGR) with amphiphilic surface was prepared from plasma surface modification of GR via optimization in gas source,discharge power,discharge time as well as working pressure,and then used as carrier for synthesis of Pt nanocatalyst(Pt/NDGR).The catalyst obtained was characterized by FTIR,Raman,element analyzer,TEM and optical contact angle measurement,and evaluated for its catalytic performance in cinnamaldehyde(CAL) hydrogenation.The results showed that nitrogen-doped GR [NDGR(O_(2)-NH_(3))] obtained by two-step plasma grafting process,which used O_(2) as plasma gas source activating GR surface and then grafted nitrogen-containing groups onto GR surface with NH_(3) as plasma gas source,exhibited the best surface properties.Compared with GR supported Pt catalyst(Pt/GR) with nitrogen doping,NDGR(O_(2)-NH_(3)) supported Pt catalyst [Pt/NDGR(O_(2)-NH_(3))],prepared under the optimal conditions of discharge power 140 W,working pressure 200 Pa and discharge time 6 min,displayed excellent catalytic performance in CAL aqueous hydrogenation reaction.Under the reaction conditions of 80 ℃,3 MPa,Pt/NDGR(O_(2)-NH_(3)) as catalyst for 4 h,the conversion rate of CAL reached 98%,the selectivity of cinnamol was ~84%,and the reaction rate constant was(1.072±0.051) h^(–1),which was much higher than that of Pt/GR as catalyst [(0.624±0.023) h^(–1)].The activation energy of the reaction was ~14 kJ/mol,only 48.3% of that of Pt/GR catalyst(about 29 kJ/mol).The high catalytic performance of Pt/NPGR(O_(2)-NH_(3)) was attributed to the increase in anchoring sites of Pt nanoparticles after a small amount of nitrogen-containing groups grafted on the surface of GR,the high adsorption performance of substrate and the synergistic effect between metal and carrier.