Synthesis and Characterisation of Hierarchically Porous HZSM-5 as Catalysts for the Synthesis of 2,3,5-Trimethyl-1,4-benzoquinone

Hierarchical HZSM-5 were synthesised by controlled desilication in alkaline medium and characterised by field-emission scanning electron microscopy, X-ray diffraction, transmission electron microscopy, inductively coupled plasma–atomic emission spectrometry, N2 adsorption–desorption, and Fourier transform infrared spectroscopy. The catalytic performance of HZSM-5 towards the selective oxidation of 2,3,6-trimethylphenol by H2O2 was evaluated. Recyclability tests were also carried out. The results showed that 2,3,5-trimethyl-1,4-benzoquinone was produced in high yields (i.e. 90 %), corresponding to a 2,3,6-trimethylphenol percentage of 98 %. The N2 adsorption–desorption and XRD studies suggested that mesopores with an average size of 5 nm were produced and that the structural character of HZSM-5 was preserved after desilication. Transmission electron microscopy analysis of the spent catalyst indicated good stability of the hierarchical structure. The Fourier transform infrared spectroscopy studies revealed the development of acid sites. The combined results suggested that the nature of the solvent, intrinsic acidity, and shape selectivity of the hierarchical structure of the catalyst ensured high catalytic properties.