| Gold catalysts exhibit much higher selectivity due to the unique properties of gold to desorb olefins than alkynes and have been consideredactive in the hydrogenation of alkynes.The catalytic activity of gold nanocatalysts was found to be lower than that of Pd and/or Ni catalysts,so efficient utilization of active metal components is one of the main challenges in Au catalysis.This question has been addressed by using Au catalysts modified with reducible oxides supports,which have potential in the selective hydrogenation of acetylene.The modulation of defect characteristics and the surface acidity/basicity of supports was used to improve the catalytic properties.The interaction between the metal and the supports was also utilized to increase the catalytic performance in the selective hydrogenation of acetylene.Herein,we prepared three kinds of nano-gold catalysts on different supports bycorrespondent methods for the selective hydrogenation of acetylene.The results showed that the conversion of acetylene was varied but the selectivity of ethylene was superior over nano-gold catalyst.These catalysts were characterized by a series of methods.Finally,the detailed conclusions are as follows:?1?The Au/CeO2 catalyst were investigated in the selective hydrogenation of acetylene to ethylene reaction.It was found that the Au catalysts of air atmosphere pretreatment increases not only the activity of the reaction,but also their selectivity at high temperature.The C2H2 conversion of Au/CeO2?R?-air catalysts was about three times as much as the Au/CeO2?R?-H2 catalysts at 300°C.The Au/CeO2?R?-air catalyst has a turnover frequencies?TOFs?value of 5.6×10-33 s-11 at 250°C for 50 min.The Au/CeO2catalysts still have good catalytic activity after 700 min of hydrogenation reaction.We found that the structural properties of the CeO2 support were not changed.The nano-gold particles was still highly dispersed and average particle sizes was small.The Au/CeO2-air catalyst has less lattice oxygen defects and better catalytic activity than the Au/CeO2-H2catalyst.Both of the morphology and the pretreatment atmosphere of supports effects the lattice oxygen deficiency,which indicates that the catalysts has an effect on the hydrogenation reaction.?2?The CeO2 modified Au/Al2O3 catalysts were investigated in the selective hydrogenation of acetylene to ethylene.All 0.3%Au/xCeO2-Al2O3 catalysts exhibited better catalytic performance than 0.3%Au/Al2O3 catalyst under the same conditions.The highest TOFs value is 10.6×10-3 s-1 for Au/0.3%CeO2-Al2O3 catalyst at 250°C,which is nearly 1.5 times of Au/Al2O3(7.2×10-3 s-1).All the three Au/xCeO2-Al2O3 catalysts show better catalytic selectivity?>95%?compared with Au/Al2O3?81%?.A series of characterization results showed that the addition of tace of CeO2 didn't change the morphology and structure of Au/Al2O3 catalysts.Moreover,the addition of CeO2 enhanced the hydrogen efflux effect on the surface of catalysts,and reduced the interaction between Au and Al2O3.With the increase of CeO2 loading,the surface acid of Au/Al2O3 was decreased.A appropriate surface acid was needed for the improvement of catalytic activities.?3?The organic heteroatom modified Au/Al2O3 catalysts were studied for selective hydrogenation of acetylene.The result indicated that the best conversion of the 0.5%Au/CN-Al2O3 catalyst,and the TOF reached 22.5×10-3 s-1 at 250°C.However,after the calcination under atmosphere,the catalytic activity of modified catalyst was changed in the acetylene hydrogenation reaction.It could be seen from the FTIR that the structure of the catalyst was the key factor affected the hydrogenation reaction.The C and N materials were coated on the surface of Al2O3 supports before the calcination.With this structure,the active Au is protected by inert organic heteroatom from the corrosion of acid,and the inert organic heteroatom is activated by the Au for catalytic hydrogenation.The assembly of them gives a new catalyst that is effective and stable for hydrogenation even under a strongly acidic environment.However,the structure tended to stabilized after calcination.A large amount of graphite carbon were formed on the surface of catalysts,which was unfavorable during hydrogenation reaction. |
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