Synthesis Of Gold Based Nanocatalysts And Their Performance In Selective Oxidation Of Ethanol

Since Professor Haruta discovered that CO oxidation reaction takes place at low temperatures when Au nanoparticles were deposited on metal oxides supports,extensive interest and efforts have been concentrated on the research and development of gold catalysts.In particular,supported Au nanocatalysts emerge as very active catalysts for liquid-phase catalytic oxidation of alcohols.However,few attentions had been given to gas-phase selective oxidation of ethanol for supported Au nanocatalysts.Acetaldehyde is a very important chemical intermediate to synthesize other chemicals.The gas-phase selective oxidation of ethanol to acetaldehyde is a promising alternative to the preparation from petroleum-based ethylene in industrial application fields.However,the low activity and selectivity in gas-phase oxidation ethanol to acetaldehyde limit the industrial application.In this dissertation,we focused on the controlled synthesis of gold nanocatalysts and their catalytic performance in gas-phase selective oxidation ethanol,in order to unveil the structure-activity relationship and to develop superior catalysts.We started from the investigation of the catalytic performance of high-quality gold-based model nanocatalyts.Based on study of catalytic performance of AuM nanocrystals,AuCu/SiO₂ catalysts exhibited remarkably improved activity.By characterizations of TEM and XPS,it is found that Au@CuO_x?core-shell?structures were formed after calcination in air.The active sites for gas-phase selective oxidation ethanol are the interface between gold and CuO_x.We then focused our study on the exploration of the structure-activity relationship of high-quality Au-based nanocatalyts.The silicates nanotubes were prepared by a hydrothermal method in water/ethanol systems.The novel catalysts were synthesized by the absorption-deposition of Au colloidal.Their catalytic performance in selective oxidation of ethanol to acetaldehyde were evaluated respectively.The result shows that Au/CuSiO₃ nanotubes display high active and selective at high gas hourly space velocity?GHSV?.The ethanol conversion can reach 98% and the selectivity to acetaldehyde is 93% at250 ? at ¹00,000 m L·gcat-1·h-1.But,the catalytic activity of Au/MgSiO₃ nanotubes is low and the ethanol conversion can only reach ²5% at 250 ?.When added Cu elements to Au/MgSiO₃,we found the catalytic activity of Au/Cu-MgSiO₃ has improved significantly.Thus,the synergistic catalytic effect between Au nanoparticles and Cu species should ascribe to the high performance for selective oxidation of ethanol to acetaldehyde.We further undertook the integrated design of Au-based nano-catalysts under the guidance of known model catalyst and structure-activity relationship to conclude the dissertation.Our purpose is to find the superior catalysts for industry vision and confirm their advantages.The chosen catalysts were prepared by ammonia evaporation and hydrothermal method.On catalysts,the copper silicates highly disperse on the SiO₂ substrate.Combining the advantages of the surface structure and composition as well as the overall morphology,the as-prepared Au/20Cu-SiO₂ catalysts exhibited superior activity and durability in the gas-phase selective oxidation ethanol to acetaldehyde.