完全氧化和部分氧化反应中CuMnOx的不同活性相

Different Active Phases of CuMnO x for Total Oxidation and Partial Oxidation

完全氧化和部分氧化反应的目标产物完全不同,而铜锰复合氧化物催化剂(CuMnO x)不仅可以催化燃烧挥发性有机物(VOCs)这样的完全氧化反应,也可以催化醇类选择氧化制醛酮这样的部分氧化反应。CuMnO x结构复杂,且对制备方法具有高度敏感性,制备方法的微小差别就可导致催化剂结构的显著差异。CuMnO x中存在不同价态的CuO x、MnO x物种,还可生成尖晶石型或者无定形的铜锰复合氧化物。CuMnO x中的这些物种在完全氧化反应和部分氧化反应中都可能存在一定的催化活性,研究者对CuMnO x的活性相还没有完全统一的认识。在醇类部分氧化反应中,CuMnO x所含的尖晶石型铜锰复合氧化物能提供移动性强的表面吸附氧物种、具有吸附-活化分子氧功能的表面氧空位以及晶格氧等多种活性氧物种。在VOCs完全氧化反应中,富含具有吸附反应物能力的Mn 4+的尖晶石型铜锰复合氧化物,具有较强的氧化还原能力,表现出高催化活性。含有丰富的Mn 3+的无定形铜锰复合氧化物也具有高催化活性,无定形铜锰复合氧化物表面发生Cu 2++Mn 3+→Cu++Mn 4+氧化还原反应是其具有高催化活性的原因。尖晶石型铜锰复合氧化物和氧化铜/氧化锰形成的复合物也可能是完全氧化反应的活性相,其中MnO x由于具备较强的储氧/释氧能力可以为尖晶石型铜锰复合氧化物提供充足的氧物种,而高度分散的CuO x能提高活化分子氧的能力,从而提高催化剂在完全氧化反应中的催化能力。本文归纳了CuMnOx在部分氧化醇类及完全氧化VOCs反应中的活性相的研究进展,对尖晶石Cux Mn3-x O4物种作为部分氧化醇类活性相进行介绍,并分析其在部分氧化反应中的氧化机理。分别对无定形Cu-Mn-O物种在完全氧化反应中的作用、尖晶石Cux Mn 3-xO4物种在完全氧化反应中的作用、尖晶石Cux Mn3-xO 4物种和氧化铜或氧化锰的复合体在完全氧化反应中的作用进行介绍,为开发高效的完全氧化和部分氧化催化剂提供参考。

The target products of total oxidation and partial oxidation are completely different.CuMnO x can catalyze total oxidation and partial oxidation reactions like the catalytic combustion of volatile organic compounds(VOCs)and the partial oxidation of alcohols to aldehydes and ketones.CuMnO x have very complex structure which is highly sensitive to their preparation strategies.Such a high sensitivity implies that a tiny change of preparation method can lead to significant differences in catalyst structure.CuO x and MnO x species with different valence states as well as spinel phase or amorphous Cu-Mn mixed oxide can be found in CuMnO x.These species are all active in either total oxidation or partial oxidation.Howe-ver,researchers have not achieved a consensus for the active phase of CuMnO x.In the partial oxidation reactions of alcohols,the active phase of CuMnO x is spinel Cu-Mn mixed oxide,which can provide a variety of active oxygen species,movable surface adsorbed oxygen species,surface oxygen vacancy and lattice oxygen species.In the total oxidation reactions of VOCs,the spinel Cu-Mn mixed oxide with high content of Mn 4+,which can adsorb reactants,present high redox performance and therefore exhibit high catalytic activity.The amorphous Cu-Mn-O species with abundant Mn 3+is also highly active due to the reaction(Cu 2++Mn 3+→Cu++Mn 4+)carrying on catalyst surface.The mixtures of spinel and MnO x or CuO x were found to be active in the total oxidation reactions.In such a mixture,MnO x species can provide sufficient molecular oxygen for the spinel species due to their high storage-release capacity of oxygen species while highly dispersed CuO x species can activate molecular oxygen.Herein,a summary of the active phases of CuMnO x in both the partial oxidation of alcohols and the total oxidation of VOCs was taken.An introduction to spinel Cu x Mn 3-x O 4 species as the active phase of the partial oxidation of alcohols and the analyzing of the partial oxidation reaction mechanism on these species were demonstrated.In order to offer an useful clue to the development of highly effective catalysts for partial oxidation and total oxidation,the roles of amorphous Cu-Mn-O species,spinel Cu x Mn 3-x O 4 species,the mixtures of spinel Cu x Mn 3-x O 4 species and copper oxide or manganese oxide compounds in total oxidation were discussed,respectively.