Studies In Preparation And Modulation Of Single-Atom Cu Catalyst For Selective Oxidation Of Benzene To Phenol

Single-atom catalysts（SAC）feature maximum metal utilization and highly tunable metal coordination structures,which endow them extraordinary catalytic performances in variety of applications.Single-atom transition metal catalysts,such as Fe and Co,have been applied in selective oxidation of benzene to phenol with applaudable performance.However,the catalytic efficiency is relatively low.In this thesis,the preparation and modulation of single-atom Cu catalysts were explored for selective oxidation of benzene to phenol.The main contents are as follows:By supramolecular preassembly and pyrolysis strategy,the copper species containing supramolecular polymer was preassembled in DMSO solution with copper nitrate,melamine and cyanic acid as raw materials,following with pyrolysis treatment,the carbonitride（CN）based single-atom catalyst with Cu₁-N₃ moieties（Cu-N₃ SA/CN）was obtained.Owing to the weak oxidation of phenol over single-atom Cu-N₃ SA/CN catalyst,it shows higher phenol selectivity（90.6%vs 64.2%）than nanoparticle catalyst in benzene selective oxidation to phenol.The single-atom Cu-N₃ SA/CN shows a 33.4%benzene conversion and 90.6%phenol selectivity with the H₂O₂/Benzene molar ratio of 12:1.Furthermore,the single-atom Cu-N₃SA/CN catalyst also shows good stability after 4 times of reaction cycle.Using chemical reduction deposition and acid leaching method,with CN as support and copper nitrate,melamine,cyanic acid as raw materials,the single-atom Cu-N₂ SA/CN catalyst with Cu₁-N₂ coordination structure was successfully fabricated.Compared with Cu₁-N₃ site,the Cu₁-N₂ site features more electron transfer with CN support and lower H₂O₂ activation energy barrier.As a result,single-atom Cu-N₂ SA/CN shows 3.4 times of TON value to single-atom Cu-N₃ SA/CN under same reaction conditions.And single-atom Cu-N₂ SA/CN shows 70.9%of benzene conversion and 91.1%of phenol selectivity with the H₂O₂/Benzene molar ratio of 10:1.Furthermore,the single-atom Cu-N₂ SA/CN catalyst also shows good stability after 4 times of reaction cycle.By supramolecular preassembly and pyrolysis strategy,the copper species containing supramolecular polymer was preassembled in aqueous solution with copper nitrate,melamine and cyanic acid as raw materials.Followed with pyrolysis treatment,the carbonitride（CN）based single-atom catalyst with Cu₁-N₁O₂ moieties（Cu-N₁O₂ SA/CN）was obtained.DFT calculations confirm that the Cu₁-N₁O₂ site features less Cu-3d electron than Cu₁-N₂ and Cu₁-N₃ sites,which promotes the adsorption and activation of reactant molecules,and provides a preponderant reaction pathway with less steps and lower energy barrier for selective oxidation of benzene to phenol.With a H₂O₂/benzene mole ratio of 2,the benzene conversion can reach to 83.7%with a phenol selectivity of 98.1%over Cu-N₁O₂ SA/CN.Furthermore,the single-atom Cu-N₁O₂ SA/CN catalyst also showed good recycling stability for 5 times of reaction cycles.