Preparation Of Iron-M Catalyst And Its Catalytic Application In Selective Hydrogenation Of Acetic Acid To Acetaldehyde

As an important intermediate in organic chemical industry,acetaldehyde?AA?has abundant downstream products including acetic ethers,pentaerythritol,glyoxal,trichloroacetaldehyde,lactic acid and pyridines,etc.As well,acetaldehyde is an important basic raw material for the synthesis of fine organic chemicals such as drugs,pesticides and spices with great value in industry application.The industrial synthesis methods of acetaldehyde mainly include ethylene oxidation,alcohol oxidation,ethanol dehydrogenation,ethane oxidation and carboxylic acid reduction.In recent years,plenty of researchers draw their attention on selective hydrogenation route of acetic acid to acetaldehyde because of its great advantages in the following three aspects:firstly,industrial production of acetic acid from syngas is a mature low-cost technology in large-scale industrialized;Secondly,the process of acetic acid hydrogenation to acetaldehyde is simple and time-efficient with high acetaldehyde selectivity and few by-products;Finally,hydrogenation catalyst can be separated from the reaction mixture to minimize pollutant emission which is also very important to environmental protection.However,the reported Fe based catalysts cannot achieve high acetic acid conversion and acetaldehyde yield due to the lack of surface oxygen vacancies,far away from requirements of industrial application.Therefore,the research emphasis in the catalysis of acetic acid hydrogenation to acetaldehyde is developing a new catalytic material with rich oxygen vacancy.In this thesis,the modified sol-gel method was used to prepare a series of Ce-Fe oxide solid solution(Ce_1-xFe_xO_2-?)catalysts and the catalyst property like structure,chemical composition,morphology,oxygen vacancy concentration was investigated by corresponding characterization technique.Subsequently,the as prepared Ce_1-x Fe_xO_2-?catalysts were applied in selective acetic acid hydrogenation to acetaldehyde.The influence of Fe doping amount x,reaction temperature and H₂ flow rate on catalytic activity were systematically studied.The results demonstrated that Ce_1-x-x Fe_xO_2-?catalysts possessed more oxygen vacancy compared with pure CeO₂ and Fe₂O₃ oxides,and Ce_0.8Fe_0.2O_2-?catalyst reach the highest oxygen vacancy concentration.The optimal 72.1%acetic acid conversion and 21.6% acetaldehyde yield were obtained when the reaction parameters were adjusted to 350? and 10 mL/min H₂ flow rate.The improved acetic acid conversion is mostly ascribed to the oxygen vacancy increase in catalyst surface.Nevertheless,acetaldehyde selectivity and yield still remain in low level because insufficient metal sites for activating H₂.So further modification of Ce-Fe oxide solid solution is necessary to acquire acetaldehyde selectivity and yield.For promoting catalytic activity to acetaldehyde,metal Co loaded Ce_0.8Fe_0.2O_2-?catalysts were synthesized via NaBH₄ reduction,and the catalyst structure comparison with pure support was carried out by various characterization methods.The results proved that the Co loaded Ce_0.8Fe_0.2O_2-?catalysts had higher oxygen vacancy concentration than pure support and better catalytic reduction performance,which indicated that the Co loading cause a positive effect on catalytic activity.In addition,the as prepared catalysts were applied in selective acetic acid hydrogenation to acetaldehyde to investigate the impact of Co loading amount.It was found that acetic acid conversion was increased up to 84.4% and acetaldehyde selectivity and yield attained almost doubled increase to 59.1% and 49.9%.The catalytic mechanism analysis manifested highly dispersed metallic Co activated the H₂ to form active hydrogen species?H·?followed by spillover onto support surface,which facilitated the surface oxygen vacancy formation and lattice oxygen transfer.Those procedures lead to the promotion effect of Co to selective acetic acid hydrogenation to acetaldehyde.This thesis researches the preparation of Ce-Fe oxide solid solution,the Co loading modification and selective acetic acid hydrogenation reaction in detail and help to solve the problem of lack of surface oxygen vacancy and metal sites for H₂ activation over the catalysts of selective acetic acid hydrogenation,which improve the acetic acid conversion and acetaldehyde yield.Meanwhile,this thesis analyzes the synergistic effect between metallic Co and Ce_1-xFe_xO_2-?supports and proposal a possible reaction mechanism,which provides a new insight for researching the catalysts of selective acetic acid hydrogenation to acetaldehyde.