Oxygen-ammonia plasma surface modified graphene for aqueous hydrogenation of cinnamaldehyde
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(O2-NH3)]obtained by two-step plasma grafting process,which used O2 as plasma gas source activating GR surface and then grafted nitrogen-containing groups onto GR surface with NH3 as plasma gas source,exhibited the best surface properties.Compared with GR supported Pt catalyst(Pt/GR)with nitrogen doping,NDGR(O2-NH3)supported Pt catalyst[Pt/NDGR(O2-NH3)],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(O2-NH3)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(O2-NH3)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.