In Situ Production Of H₂O₂ During Au/C Catalyzed Aerobic Oxidation Of 1,2-propanediol And Kinetic Mechanism Exploration

Alcohols oxidation catalytically are mainly used to produce added value acids selectively,people have never explored the kinetics of H₂O₂formed as a byproduct.Nowadays,the process of H₂O₂ production are traditional AO(Anthraquinone Oxidation)and direct synthesis.However,AO process will produce a lot of organic solvents during the process,its disadvantage is to cause the pollution to the environment.As for direct synthesis from H₂ and O₂,they will be explosive if the ration of two gases is not correct.This study focuses on 1,2-propanediol,which is a product of glycerol dehydration or hydrogenation,during Au/C catalyzed aerobic oxidation under atmospheric pressure and close to room temperature 35°C in this thesis,at the same time the study also investigates fatty alcohols and aromatic alcohols oxidation and have a comparison with 1,2-propanediol,then try to find the kinetic relationship between them.Propose the reaction mechanism and analyze reaction routes.The results can be concluded as below:(1)Alcohols reaction and acids formation detected by HPLC,H₂O₂ accumulation concentration measured by UV-Vis.Ti O₂ and Si O₂ are not suitable for basic reaction condition,so we choose activated carbon as support due to large specific surface area,cheaper and abundant pore structure.Au is a better choice because of good property and stable under O₂ atmosphere.Based on these,we choose the Au/C prepared by Deposition precipitation method,the catalyst is very stable and can catalyze substrate under basic condition.(2)The efficiency of H₂O₂ formation increased with increasing concentration of 1,2-propanediol and Na OH,but the increasing rates become slow.H₂O₂ concentration reached a maximum after 15 min also of reaction and then has a stable trend.The decline in H₂O₂ concentration was attributed to its degradation through catalytic decomposition and reaction with 1,2-propanediol/diolate as well as the slow deactivation of the catalyst.Before and after reaction of Au/C have a series of characterization,TEM,XPS,BET to have a comparison.But the results show they don't have a big difference.The reason maybe some stable oligomeric species generated during oxidation process block the active sites on the surface of Au/C.(3)The primary role of hydroxide ion is in deprotonating the diol and it is not involved in the rate limiting step.Data gathered at different concentrations of diol and Na OH established a linear relationship between the reciprocal rate of 1,2-propanediol oxidation and the inverse of the diolate concentration.The data indicated that when a full surface coverage of diolate was achieved,one molecule of H₂O₂ would be produced for every molecule of diol oxidized.At lower than saturation coverage of the diolate,unoccupied active sites adjacent to adsorbed hydroperoxy or peroxy enabled cleavage of the O?O bond,which resulted in nonproductive H₂O₂ possibly.(4)The p Ka of 1,2-propanediol,allyl alcohol,benzyl alcohol and 1-phenylethanol are 14.9,16.2,15.4 and 14.8,respectively.?C-H bond energy are 399.2?335.1?351.5and 355.6 k J/mol,respectively.4 types of alcohols oxidation under the same condition results suggest that the amounts of H₂O₂accumulated in situ is closely related to the alcohols'p Ka and?C-H bond energy.Further reaction of fluorinated alcohols(1,1,1,3,3,3-hexafluoro-2-propanol)cannot produce H₂O₂.It suggests that 2H of H₂O₂ are from?C-H of alcohol.