Preparation and characterization of Silicalite-1 zeolites with high manganese contents from mechanochemically pretreated reactants

Silicalite-1 zeolites with high manganese contents isomorphously incorporated within the framework were synthesized by using mechanochemical pretreatment. First, manganese and silica sources were mixed in a planetary ball mill to obtain a composite material comprised of Mn, Si, and O. The composite was subsequently hydrothermally treated to crystallize Silicalite-1 zeolites. The synthesis was performed using a condition with a small amount of water to directly convert the composite material into a zeolite crystal while preventing manganese from leaching into water, which may cause manganese oxide/hydroxide species to precipitate. X-ray fluorescence analysis showed that the obtained products displayed a high manganese content of up to 6.3 mol%. The importance of utilizing mechanochemical treatment was confirmed through a number of characterization techniques, such as X-ray diffraction, catalytic activity assessments, diffuse reflectance UV-vis spectroscopy, Raman spectroscopy, and X-ray absorption fine structure analysis. Our findings suggest that this procedure using mechanochemical pretreatment can produce zeolites with various heteroatoms within their framework structures at contents difficult to achieve through conventional methods.