The Study Of Pt/Co₃O₄ Catalysts For Higher Alcohols Synthesis From CO₂ Hydrogenation

The emission of CO₂ continuous increased with the development of the transportation and industry.A effective method to utilize the abundant CO₂ will not only ease up the increasing greenhouse effect,but also solve the energy shortage problem.The synthesis of higher alcohols from CO₂ hydrogenation reaction is a promising route of CO₂ resource utilization.But there are still some problems to be solved,such as the difficult activation of CO₂,the low selectivity of higher alcohols and so on.In recent years,the study of catalysts on higher alcohols synthesis from CO₂ hydrogenation indicated that the surface of reductive oxide?such as Co₃O₄?supporter was rich of oxygen vacancy defect.The oxygen vacancy defect can promote the adsorption and dissociative of CO₂,and catalyze the activation of CO₂ in the mild condition.Co based catalyst has the ability to improve the growth of the carbon chain.Noble metal Pt has the reverse water-gas shift reaction activity.All of them together will promote the higher alcohols synthesis from CO₂ hydrogenation.In this thesis,Co₃O₄ oxides were synthesized by different ways.The Co based catalysts were prepared with partial reduced Co₃O₄,noble metal Pt was added as the promoter.The effect of the morphologies,pore structures of Co₃O₄ oxide and Pt promoter in the catalysts was studied in higher alcohols synthesis reaction from CO₂hydrogenation.The work details were stated as follows:?1?The Co₃O₄ oxides with different morphologies?nanorods and nanoplates?were prepared,the Pt/Co₃O₄ catalysts were then prepared by incipient-wetness impregnation method.Characterization and reaction results showed that the reducing property of Pt/Co₃O₄-p was better than Pt/Co₃O₄-r catalyst,more Co₃O₄ was reduced to metallic Co under the same reduction temperature.The more metallic Co resulted in the initial activity of Pt/Co₃O₄-p was higher than Pt/Co₃O₄-r.But the activity of Pt/Co₃O₄-p obviously decreased in 50 reaction hours due to its low surface area of Co₃O₄-p.The Pt/Co₃O₄-r gave a stable activity during the reaction.The CO₂conversion of Pt/Co3O4-r catalyst was 27.8%and the yield of higher alcohols was0.54 mmol·g^-1·h^-11 under the 200?r eaction temperature after H₂ reduction at 200?.?2?The ordered mesoporous Co3O4 oxide?Co3O4-m?was synthesized by KIT-6as the hard template and Co?NO₃?₂ as the cobalt precursor.Nano particle Co₃O₄ oxide was prepared by coprecipitation method at the same time.The two Co₃O₄ oxides with different pore structures were tested for the catalytic performance of CO₂hydrogenation.Characterization and reaction results showed that the ordered mesoporous structure of Co₃O₄-m catalyst could promote the growth of carbon chain,and reduce the selectivity of CH₄.The best yield of higher alcohols(1.56 mmol·g^-1·h^-1)and the conversion of CO₂?28.9%?was obtained for Co₃O₄-m under the 200?reaction temperature after reduction at 300?.In order to reduce the by-product selectivity of CH₄,noble metal Pt was introduced to Co₃O₄-m catalyst.The study showed that the selectivity of CH₄ decreased,and the selectivity of CO and alcohols increased in Pt/Co3O4-m catalyst owing to the RWGS ability of Pt.However,the conversion of CO₂ obviously reduced at the same time.The yield of higher alcohols(1.48 mmol·g^-1·h^-1)was slightly lower than Co₃O₄-m catalyst under the same condition.