Streamlined synthesis of iron and cobalt loaded MCM-48: High-performance heterogeneous catalysts for selective liquid-phase oxidation of toluene to benzaldehyde

Abstract

Hydrothermal synthesis of MCM-48 molecular sieves featuring the incorporation of both iron and cobalt with Si/M ratios of 20, 40 and 80 (where M represents either iron or cobalt) was performed using tetraethyl orthosilicate as the silica source and cetyltrimethylammonium bromide as a template. To gain a comprehensive understanding of the synthesized materials, these were thoroughly characterized using various techniques, including XRD, XPS, UV–Vis (DRS), FT-IR, N₂ adsorption-desorption analysis, SEM with EDX, TEM, TGA and NH₃-TPD analysis. XRD analysis revealed the presence of well-ordered MCM-48 structure in the metal-incorporated materials, while XPS and UV–Vis DRS confirmed the successful partial incorporation of metal ions precisely in their desired tetrahedral coordination within the framework. To assess their catalytic performance, we studied the activity and selectivity of these catalysts in liquid phase oxidation of toluene using tert-butyl hydroperoxide as the oxidant. Under optimized conditions, employing a 6% (w/w) Fe-MCM-48 (40) catalyst and maintaining a toluene to oxidant molar ratio of 1:3 at 353 K in a solvent-free environment for 8 h, the oxidation reaction resulted in the formation of benzaldehyde (88.1%) as the major product and benzyl alcohol (11.9%) as the minor product.