Modification Of Manganese-based Catalyst And Its Application In Catalytic Oxidation Reaction

Introducing copper to manganese oxides to prepare copper-manganese dual-component oxide catalysts（Cu-Mn-O）.The Cu-Mn-O catalysts were widely used in complete oxidation due to its advantages of low-price,wide source of raw materials,and high adjustable structure.Extending the application of this classic complete oxidation catalyst to selective oxidation of alcohols can not only greatly expand the application scope of this non-noble metal oxide catalyst system,but also greatly enrich the selection possibilities of selective oxidation catalysts,with both practical and catalytic scientific values.However,Cu-Mn-O catalyst as a very complex transition metal oxide system and extremely sensitive to the preparation method and conditions.The copper oxides（CuO_x）,manganese oxides（MnO_x）and spinel(Cu _XMn_3-XO₄)always co-exist in different combinations in Cu-Mn-O catalyst with the change of preparation method or preparation parameters which makes it is hard to achieve a unfied and clear understanding of the active phase in Cu-Mn-O catalyst.Therefore,it is very important to take appropriate approaches to deeply study the formation mechanism and distribution of oxide species in Cu-Mn-O catalysts for the development of efficient Cu-Mn-O catalysts.In this paper,a series of copper modified manganese catalysts were prepared by biological carbon template method,biological carbon template impregnation-grinding method and foam-grinding method.The structural characteristics of these Cu-Mn-O catalysts and the evolution of the“oxide pair”structure contained in these Cu-Mn-O catalysts were studied by XRD,TEM,H₂-TPR,Raman,FT-IR,and XPS characterization methods.The changes in catalytic performance of these Cu-Mn-O catalysts in the selective oxidation of benzyl alcohol were also studied in this paper.It was found that the Cu-Mn-O catalyst exhibited excellent catalytic performance in the catalytic oxidation of benzyl alcohol using H₂O₂ as oxidant,achieving a conversion of 63%of benzyl alcohol and a selectivity of nearly 100%for benzaldehyde.The Cu⁺species in the Cu-Mn-O catalyst can efficiently decompose H₂O₂ into·OH,enabling the activation and selective oxidation of benzyl alcohol to proceed through a Fenton-like mechanism.The spinel phase Cu _XMn_3-XO₄ species formed in Cu-Mn-O catalysts contain abundant Cu⁺species,which are key species for their high activity and selectivity in the selective oxidation of benzyl alcohol using H₂O₂ as oxidant.If Cu-Mn-O catalysts contain oxides such as CuO_x,MnO_x,and Cu _XMn_3-XO₄ simultaneously,then it is difficult to obtain high catalytic activity.The“oxide pair”structure composed of different oxide species such as CuO_x,MnO_x,and Cu _XMn_3-XO₄ provides the active sites of Cu-Mn-O catalysts.Compared with Cu-Mn-O catalysts containing mainly Cu O-Cu_1.4Mn_1.6O₄ and Mn₃O₄-Cu_1.4Mn_1.6O₄“oxide pairs”,Cu-Mn-O catalysts containing only Mn₂O₃-Cu_1.4Mn_1.6O₄“oxide pairs”have higher selective oxidation activity for benzyl alcohol.Using“oxide pair”to study the interactions between different oxide species that make up“oxide pairs”,we can deeply understand the essence of the synergistic effects between Cu and Mn elements in Cu-Mn-O catalysts.