Promotion Effect of Mn on the Mo-Bi-Fe-Co-Cs-K Composite Oxide Catalysts for Selective Oxidation of Isobutene to Methacrolein

Mn promoted Mo-Bi based composite oxide catalysts were prepared by coprecipitation method and were tested for selective oxidation of isobutene to methacrolein(MAL).Catalytic reaction was carried out in a fixed-bed micro-reactor at atmospheric pressure.The surface area and structure of the catalysts were characterized by BET and XRD.It was found that addition of Mn(NO3)2 to Mo-Bi-Fe-Co-Cs-K composite oxide promotes the formation of Bi3FeMo2O12,which is favorable to enhance isobutene conversion of the catalyst.When Mn promoter was introduced to the Mo-Bi-Fe-Co-Cs-K composite oxide using MnMoO4 as precursor,both activity and selectivity of the catalyst can be significantly improved.Under the reaction conditions of 400 ℃ and GHSV=2 000 mL·g-1·h-1 using an air∶ isobutene=10∶ 1(volume ratio) mixture as reactant.Isobutene conversion of 92.8 % with MAL selectivity of 93.5% can be achieved.The performance of the catalyst remained stable after 72 h on stream.The results of XRD characterization indicated that the excellent performance of the catalyst was closely related to the formation of a new compound with XRD diffraction peaks at 25.6 at 28.5,which can significantly improve the selectivity of the catalyst especially at high isobutene conversion.